Termite mounds harness diurnal temperature oscillations for ventilation

Termites can learn

It is generally believed that termites can't learn and are not "intelligent". This study aimed to test whether termites could have any form of memory. A Y-shaped test device with one release chamber and two identical test chambers was designed and constructed by 3D printing. A colony of damp wood termites was harvested from the wild. Worker termites were randomly selected for experiment. Repellent odors that could mimic the alarm pheromone for termites were first identified. Among all substances tested, a tea tree oil and lemon juice were found to contain repellent odors for the tested termites, as they significantly reduced the time that termites spent in the chamber treated with these substances. As control, a trail pheromone was found to be attractive. Subsequently, a second cohort of termites were operant conditioned by punishment using both tea tree oil and lemon juice, and then tested for their ability to remember the path that could lead to the repellant odors. The test device was thoroughly cleaned between trials. It was found that conditioned termites displayed a reduced tendency to choose the path that led to expectant punishment as compared with naïve termites. Thus, it is concluded that damp wood termites are capable of learning and forming "fear memory", indicative of "intelligence" in termites. This result challenges established presumption about termites' intelligence.

Desiccation tolerance of Termitidae termites in relation to their nest type

The family Termitidae is renowned for its diverse nesting behaviors, with the evolution of epigeal and arboreal nests hypothesized to increase desiccation stress due to greater exposure to air. However, these nests may also alleviate desiccation stress through humidity regulation. To explore the implications of acquiring epigeal and arboreal nests, we investigated desiccation tolerance traits in 16 Termitidae termite species with varying nest types and analyzed trait correlations. Principal component analysis revealed that termites constructing epigeal and arboreal nests exhibited reduced water loss rates and enhanced survival under desiccated conditions. Furthermore, termites building arboreal nests displayed a notably higher water content. Redundancy analysis demonstrated that nest types accounted for a substantial portion (57.2%) of the observed variation in desiccation tolerance. These findings support the hypothesis that epigeal and arboreal nests in termites are associated with increased desiccation stress and increased desiccation tolerance. These findings highlight the role of nest type in influencing desiccation tolerance mechanisms and water regulation strategies in termites.

Animal homing: Ants build their own landmarks when they need them

Visual landmarks are extremely useful for successful navigation in many species, including ants. So much so that a new study shows that desert ants actually build their own landmarks when they need them.

Culture Conditions for Mycelial Growth and Anti-Cancer Properties of Termitomyces

Termitomyces sp. that grow in symbiosis with fungus-farming Termites have medicinal properties. However, they are rare in nature, and their artificial culture is challenging. The expression of AXL receptor tyrosine kinase and immune checkpoint molecules favor the growth of cancer cells. The study evaluated the optimal conditions for the artificial culture of Termitomyces and their inhibitory activity on AXL and immune checkpoint molecules in lung adenocarcinoma and melanoma cell lines. The culture of 45 strains of Termitomyces was compared. Five strains with marked growth rates were selected. Four of the selected strains form a single cluster by sequence analysis. The mycelium of 4 selected strains produces more fungal mass in potato dextrose broth than in a mixed media. The bark was the most appropriate solid substrate for Termitomyces mycelia culture. The mycelium of all five selected strains showed a higher growth rate under normal CO₂ conditions. The culture broth, methanol, and ethyl acetate of one selected strain (T-120) inhibited the mRNA relative expression of AXL receptor tyrosine kinase and immune checkpoint molecules in cancer cell lines. Overall, these results suggest the potential usefulness of Termitomyces extracts as a co-adjuvant therapy in malignant diseases.

Remote Sensing and GIS-Based Suitability Mapping of Termite Habitat in the African Savanna: A Case Study of the Lowveld in Kruger National Park

Termites (Isoptera) are among the most globally dominant macroinvertebrates in terrestrial environments and are an ecologically important group of soil biota in tropical and subtropical ecosystems. These insects function as essential ecosystem engineers that facilitate nutrient cycling, especially in the regulation of the physical and chemical properties of soil and the decomposition of organic matter that maintains heterogeneity in tropical and subtropical ecosystems. Termites, like all living organisms, require certain environmental parameters to support the distribution, abundance, and activities of the species. South Africa’s Kruger National Park (KNP)—one of the most important protected areas in the world and a popular safari tourist destination—is an extraordinary savanna ecosystem in which termite mounds, or termitaria, are widely distributed. A range of biotic and abiotic factors found in the natural environment of KNP provide highly suitable ecological conditions for termite habitat range, and thus the development of termitaria. Previous research has shown that the most important factors affecting habitat suitability for termites and the geographic distribution of termitaria include climate factors, land cover, and other environmental characteristics such as soil composition and plant-litter biomass. However, the specific environmental mechanisms that regulate termite occurrence and the spatial distribution of termitaria in KNP are not fully understood, especially in the context of climate and land-cover changes. The present study examines the relationship between the spatial distribution of termitaria and selected climate and environmental factors in the Kruger Lowveld region, which contains one of the largest numbers of termitaria in KNP. Using high-resolution satellite imagery, 8200 training points of termitaria occurrence were collected throughout the study area to train classifiers and produce land-cover-classification maps for the Kruger Lowveld region of interest. We then applied a hybrid approach through the integration of remote sensing (RS) and a GIS-based analytical hierarchy process (AHP) and frequency-ratio (FR) methods to model the relationship between the spatial distribution of termitaria and selected environmental variables and to produce suitability maps. To our knowledge, this study is the first of its kind to examine the influence of combined sets of environmental attributes on the spatial distribution of termitaria in the Lowveld region of KNP. The results indicate that moderately and highly suitable conditions for termite range tolerance and termitaria development are correlated with undulating plains with clay soils, greater distance to drainage streams, high solar radiation, and low depth of groundwater. The findings of this study shed light on the need for future research that investigates the impact of climate and land-cover changes on termite habitat range and spatial distribution and that can inform park managers and policymakers about Kruger National Park and other protected areas with similar environmental conditions.

Thermoregulatory morphodynamics of honeybee swarm clusters

During reproductive swarming, honeybees clusters of more than 10,000 individuals that hang from structures in the environment (e.g., tree branches) are exposed to diurnal variations in ambient temperature for up to a week. Swarm clusters collectively modulate their morphology in response to these variations (i.e., expanding/contracting in response to heating/cooling) to maintain their internal temperature within a tolerable range and to avoid exhausting their honey stores prematurely. To understand the spatiotemporal aspects of thermoregulatory morphing, we measured the change in size, shape and internal temperature profiles of swarm clusters in response to dynamic temperature ramp perturbations. We see that swarm clusters show a two-fold variation in their volume/density when heated from 15°C to 30°C. However, they do not reach an equilibrium size or shape when held at 30°C for 5 hours, long after the core temperature of the cluster has stabilized. Furthermore, the changes in cluster shape and size are hysteretic, contracting in response to cooling faster than expanding in response to heating. Although the base contact diameter of the cluster increased continuously when the swarm is heated, the change in length of the swarm (base totip) over time is non-monotonic. Consequently, the aspect ratio of the swarm fluctuated continuously even when held at a constant temperature. Taken together, our results quantify the hysteretic and anisotropic morphological responses of swarm clusters to ambient temperature variations while suggesting that both mechanical constraints and heat transfer govern their thermoregulatory morphodynamics.

Modularity and connectivity of nest structure scale with colony size

Large body sizes have evolved structures to facilitate resource transport. Like unitary organisms, social insect colonies must transport information and resources. Colonies with more individuals may experience transport challenges similar to large-bodied organisms. In ant colonies, transport occurs in the nest, which may consist of structures that facilitate movement. We examine three attributes of nests that might have evolved to mitigate transport challenges related to colony size: (1) subdivision-nests of species with large colonies are more subdivided to reduce crowd viscosity; (2) branching-nest tunnels increase branching in species with large colonies to reduce travel distances; and (3) shortcuts-nests of species with large colonies have cross-linking tunnels to connect distant parts of the nest and create alternative routes. We test these hypotheses by comparing nest structures of species with different colony sizes in phylogenetically controlled meta-analyses. Our findings support the hypothesis that nest subdivision and branching evolved to mitigate transport challenges related to colony size. Nests of species with large colonies contain more chambers and branching tunnels. The similarity in how ant nests and bodies of unitary organisms have evolved in response to increasing size suggests common solutions across taxa and levels of biological organization.

Carbon dioxide levels and ventilation in Acromyrmex nests: significance and evolution of architectural innovations in leaf-cutting ants

Leaf-cutting ant colonies largely differ in size, yet all consume O2 and produce CO2 in large amounts because of their underground fungus gardens. We have shown that in the Acromyrmex genus, three basic nest morphologies occur, and investigated the effects of architectural innovations on nest ventilation. We recognized (i) serial nests, similar to the ancestral type of the sister genus Trachymyrmex, with chambers excavated along a vertical tunnel connecting to the outside via a single opening, (ii) shallow nests, with one/few chambers extending shallowly with multiple connections to the outside, and (iii) thatched nests, with an above-ground fungus garden covered with plant material. Ventilation in shallow and thatched nests, but not in serial nests, occurred via wind-induced flows and thermal convection. CO2 concentrations were below the values known to affect the respiration of the symbiotic fungus, indicating that shallow and thatched nests are not constrained by harmful CO2 levels. Serial nests may be constrained depending on the soil CO2 levels. We suggest that in Acromyrmex, selective pressures acting on temperature and humidity control led to nesting habits closer to or above the soil surface and to the evolution of architectural innovations that improved gas exchanges.

How does climate change affect social insects?

Climate change poses a major threat to global biodiversity, already causing sharp declines of populations and species. In some social insect species we already see advanced phenologies, changes in distribution ranges, and changes in abundance Rafferty (2017) and Diamond et al. (2017). Physiologically, social insects are no different from solitary insects, but they possess a number of characteristics that distinguish their response to climate change. Here, we examine these traits, which might enable them to cope better with climate change than solitary insects, but only in the short term. In addition, we discuss how climate change will alter biotic interactions and ecosystem functions, and how it will affect invasive social insects.

The role of mound functions and local environment in the diversity of termite mound structures

Mound structures that soil termites build have diverse morphologies. Previous observational studies documented that mounds are built to provide regulated environments for the termites that live within them and their structures are formed in ways to support this purpose under the influence of the mounds' immediate environment. The objective of this study is to provide a methodology and a predictive computational model to investigate the reason behind the different but systematic shapes of termite mounds, considering all the relevant forces imposed on them and their thermoregulatory and gas-exchange functions. The gas-exchange function accounts for the capacity of the mound to diffuse metabolic gases generated in the mound's underground nest, while the thermoregulatory function satisfies the connection between the underground nest and deep ground temperatures. The proposed predictive model is based on the principles of heat transfer and thermodynamics and allows optimized mechanically stable structures to freely emerge. The results indicate that, while the model is free to generate any mechanically stable structure, under the relevant environmental and metabolic conditions, it produces structures with forms and geometrical characteristics similar to those of natural mounds. Investigation of the connection between the local environment and the mound shapes indicated that the Sun and wind play an important role in the mound structural form. Mounds exposed to stronger solar irradiance exhibit cone-shaped structures that are pointed towards the Sun, while shaded mounds are observed to be vertical domes. The local wind is observed to affect the external shape of the mound by preventing them to grow tall while controlling the features of the internal structure. By investigating the similarities between structures in different regions (i.e., India, Namibia, and Brazil), it is revealed that, unlike mounds with a strong need for gas-exchange, mounds with a significant demand for thermoregulation exhibit deeper nests, thicker external walls, and well-defined cone- (as opposed to the dome-) shaped structures. Overall, the form of termite mounds is strongly correlated to both regulatory functions and local environments, and the resulting mound shape arises as a combination of these factors.

Validating a Termite-Inspired Construction Coordination Mechanism Using an Autonomous Robot

Many species of termites build large, structurally complex mounds, and the mechanisms behind this coordinated construction have been a longstanding topic of investigation. Recent work has suggested that humidity may play a key role in the mound expansion of savannah-dwelling Macrotermes species: termites preferentially deposit soil on the mound surface at the boundary of the high-humidity region characteristic of the mound interior, implying a coordination mechanism through environmental feedback where addition of wet soil influences the humidity profile and vice versa. Here we test this potential mechanism physically using a robotic system. Local humidity measurements provide a cue for material deposition. As the analogue of the termite's deposition of wet soil and corresponding local increase in humidity, the robot drips water onto an absorbent substrate as it moves. Results show that the robot extends a semi-enclosed area outward when air is undisturbed, but closes it off when air is disturbed by an external fan, consistent with termite building activity in still vs. windy conditions. This result demonstrates an example of adaptive construction patterns arising from the proposed coordination mechanism, and supports the hypothesis that such a mechanism operates in termites.

Submillimetre mechanistic designs of termite-built structures

Termites inhabit complex underground mounds of intricate stigmergic labyrinthine designs with multiple functions as nursery, food storage and refuge, while maintaining a homeostatic microclimate. Past research studied termite building activities rather than the actual material structure. Yet, prior to understanding how multi-functionality shaped termite building, a thorough grasp of submillimetre mechanistic architecture of mounds is required. Here, we identify for Nasutitermes exitiosus via granulometry and Fourier transform infrared spectroscopy analysis, preferential particle sizes related to coarse silts and unknown mixtures of organic/inorganic components. High-resolution micro-computed X-ray tomography and microindentation tests reveal wall patterns of filigree laminated layers and sub-millimetre porosity wrapped around a coarse-grained inner scaffold. The scaffold geometry, which is designed of a lignin-based composite and densely biocementitious stercoral mortar, resembles that of trabecula cancellous bones. Fractal dimension estimates indicate multi-scaled porosity, important for enhanced evaporative cooling and structural stability. The indentation moduli increase from the outer to the inner wall parts to values higher than those found in loose clays and which exceed locally the properties of anthropogenic cementitious materials. Termites engineer intricately layered biocementitious composites of high elasticity. The multiple-scales and porosity of the structure indicate a potential to pioneer bio-architected lightweight and high-strength materials.

Self-organized biotectonics of termite nests

The termite nest is one of the architectural wonders of the living world, built by the collective action of workers in a colony. Each nest has several characteristic structural motifs that allow for efficient ventilation, cooling, and traversal. We use tomography to quantify the nest architecture of the African termite Apicotermes lamani, consisting of regularly spaced floors connected by scattered linear and helicoidal ramps. To understand how these elaborate structures are built and arranged, we formulate a minimal model for the spatiotemporal evolution of three hydrodynamic fields-mud, termites, and pheromones-linking environmental physics to collective building behavior using simple local rules based on experimental observations. We find that floors and ramps emerge as solutions of the governing equations, with statistics consistent with observations of A. lamani nests. Our study demonstrates how a local self-reinforcing biotectonic scheme is capable of generating an architecture that is simultaneously adaptable and functional, and likely to be relevant for a range of other animal-built structures.

Insect architecture: structural diversity and behavioral principles

Insects build myriad structures out of diverse materials. These structures serve purposes that range from facilitating prey capture to housing their entire colony. Whereas some insects operate solitarily, others collectively build large and complex structures. The architecture of these structures vis-à-vis their ultimate function poses fascinating questions that require multidisciplinary investigations. Importantly, because the underlying design and architectural principles have evolved over millions of years to withstand multitude of environmental perturbations, they offer important lessons for human-made structures. The vast variety of insect-built structures reflects how diverse insects have adapted to resolve the ecological challenges in their specific habitats. Here, we survey insect-built structures from a comparative perspective to ask what design and architectural principles can be gleaned from them. We discuss the key hypotheses about building-behaviours, their neural underpinnings, the functional role of insect-built structures and their biomimetic potential.

Termite mounds contain soil-derived methanotroph communities kinetically adapted to elevated methane concentrations

Termite mounds have recently been confirmed to mitigate approximately half of termite methane (CH4) emissions, but the aerobic CH4 oxidising bacteria (methanotrophs) responsible for this consumption have not been resolved. Here, we describe the abundance, composition and CH4 oxidation kinetics of the methanotroph communities in the mounds of three distinct termite species sampled from Northern Australia. Results from three independent methods employed show that methanotrophs are rare members of microbial communities in termite mounds, with a comparable abundance but distinct composition to those of adjoining soil samples. Across all mounds, the most abundant and prevalent methane monooxygenase sequences were affiliated with upland soil cluster α (USCα), with sequences homologous to Methylocystis and tropical upland soil cluster (TUSC) also detected. The reconstruction of a metagenome-assembled genome of a mound USCα representative highlighted the metabolic capabilities of this group of methanotrophs. The apparent Michaelis-Menten kinetics of CH4 oxidation in mounds were estimated from in situ reaction rates. Methane affinities of the communities were in the low micromolar range, which is one to two orders of magnitude higher than those of upland soils, but significantly lower than those measured in soils with a large CH4 source such as landfill cover soils. The rate constant of CH4 oxidation, as well as the porosity of the mound material, were significantly positively correlated with the abundance of methanotroph communities of termite mounds. We conclude that termite-derived CH4 emissions have selected for distinct methanotroph communities that are kinetically adapted to elevated CH4 concentrations. However, factors other than substrate concentration appear to limit methanotroph abundance and hence these bacteria only partially mitigate termite-derived CH4 emissions. Our results also highlight the predominant role of USCα in an environment with elevated CH4 concentrations and suggest a higher functional diversity within this group than previously recognised.

Revisiting stigmergy in light of multi-functional, biogenic, termite structures as communication channel

Termite mounds are fascinating because of their intriguing composition of numerous geometric shapes and materials. However, little is known about these structures, or of their functionalities. Most research has been on the basic composition of mounds compared with surrounding soils. There has been some targeted research on the thermoregulation and ventilation of the mounds of a few species of fungi-growing termites, which has generated considerable interest from human architecture. Otherwise, research on termite mounds has been scattered, with little work on their explicit properties. This review is focused on how termites design and build functional structures as nest, nursery and food storage; for thermoregulation and climatisation; as defence, shelter and refuge; as a foraging tool or building material; and for colony communication, either as in indirect communication (stigmergy) or as an information channel essential for direct communication through vibrations (biotremology). Our analysis shows that systematic research is required to study the properties of these structures such as porosity and material composition. High resolution computer tomography in combination with nonlinear dynamics and methods from computational intelligence may provide breakthroughs in unveiling the secrets of termite behaviour and their mounds. In particular, the examination of dynamic and wave propagation properties of termite-built structures in combination with a detailed signal analysis of termite activities is required to better understand the interplay between termites and their nest as superorganism. How termite structures serve as defence in the form of disguising acoustic and vibration signals from detection by predators, and what role local and global vibration synchronisation plays for building are open questions that need to be addressed to provide insights into how termites utilise materials to thrive in a world of predators and competitors.

Bi-layered architecture facilitates high strength and ventilation in nest mounds of fungus-farming termites

Mass–energy transfer across the boundaries of living systems is crucial for the maintenance of homeostasis; however, it is scarcely known how structural strength and integrity is maintained in extended phenotypes while also achieving optimum heat–mass exchange. Here we present data on strength, stability, porosity and permeability of termite mounds of a fungus-farming species, Odontotermes obesus. We demonstrate that the termite mound is a bi-layered structure with a dense, strong core and a porous shell that is constantly remodelled. Its safety factor is extraordinarily high and is orders of magnitude higher than those of human constructions. The porous peripheries are analogous to the mulch layer used in agriculture and help in moisture retention crucial for the survival of fungus gardens, while also allowing adequate wind-induced ventilation of the mounds. We suggest that the architectural solutions offered by these termites have wider implications for natural and industrial building technologies.

Moisture alone is sufficient to impart strength but not weathering resistance to termite mound soil

Soil is used for the construction of structures by many animals, at times admixed with endogenous secretions. These additives, along with soil components, are suggested to have a role in biocementation. However, the relative contribution of endogenous and exogenous materials to soil strength has not been adequately established. Termite mounds are earthen structures with exceptional strength and durability including weathering resistance to wind and rain. With in situ and laboratory-based experiments, we demonstrate that the fungus-farming termite Odontotermes obesus which builds soil nest mounds, when given a choice, prefers soil close to its liquid limit for construction. At this moisture content, the soil-water mixture alone even in the absence of termite handling undergoes self-weight consolidation and upon drying attains a monolithic, densely packed structure with compressive strength comparable to the in situ strength of the mound soil; however, the soil-water mixture alone has lower resistance to water erosion than the in situ mound samples, suggesting that termite secretions impart weathering resistance and thereby long-term stability to the mound. Therefore, weathering resistance and compressive strength are conferred by different aspects of termite soil manipulation. Our work provides novel insights into termite mound construction and strength correlates for earthen structures built by animals.

The extension of internal humidity levels beyond the soil surface facilitates mound expansion in Macrotermes

Termites in the genus Macrotermes construct large-scale soil mounds above their nests. The classic explanation for how termites coordinate their labour to build the mound, based on a putative cement pheromone, has recently been called into question. Here, we present evidence for an alternate interpretation based on sensing humidity. The high humidity characteristic of the mound's internal environment extends a short distance into the low-humidity external world, in a 'bubble' that can be disrupted by external factors like wind. Termites transport more soil mass into on-mound reservoirs when shielded from water loss through evaporation, and into experimental arenas when relative humidity is held at a high value. These results suggest that the interface between internal and external conditions may serve as a template for mound expansion, with workers moving freely within a zone of high humidity and depositing soil at its edge. Such deposition of additional moist soil will increase local humidity, in a feedback loop allowing the 'interior' zone to progress further outward and lead to mound expansion.

The effect of nest topology on spatial organization and recruitment in the red ant Myrmica rubra

Nests of social insects are an important area for the exchange of food and information among workers. We investigated how the topology of nest chambers (as opposed to nest size or environmental factors) affects the spatial distribution of nestmates and the foraging behavior of Myrmica rubra ant colonies. Colonies were housed in artificial nests, each with same-sized chambers differing in the spatial arrangement of galleries. A highly connected central chamber favored higher occupancy rates and a more homogeneous distribution of ants across chambers. In contrast, a chain of successive chambers led to a more heterogeneous distribution of ants, with the occupancy of a chamber chiefly mediated by its distance to the entrance. Irrespective of nest topology, the entrance chamber housed the largest proportion of ants, often including the queen, which exhibited a preference for staying in densely populated chambers. Finally, we investigated how nest topology influenced nestmate recruitment. Surprisingly, a highly connected chamber in the center of the nest did not promote greater recruitment nor activation of ants. At the onset of foraging, the largest number of moving ants was reached in the topology where the most connected chamber was the nest entrance. Later in the process, we found that a chain of successive chambers was the best topology for promoting ant's mobilization. Our work demonstrates that nest topology can shape the spatial organization and the collective response of ant colonies, thereby taking part in their adaptative strategies to exploit environmental resources.

Diel pattern driven by free convection controls leaf-cutter ant nest ventilation and greenhouse gas emissions in a Neotropical rain forest

Leaf-cutter ant nests are biogeochemical hot spots where ants live and import vegetation to grow fungus. Metabolic activity and (in wet tropical forests) soil gas flux to the nest may result in high nest CO₂ concentrations if not adequately ventilated. Wind-driven ventilation mitigates high CO₂ concentrations in grasslands, but little is known about exchange for forest species faced with prolonged windless conditions. We studied Atta cephalotes nests located under dense canopy (leaf area index > 5) in a wet tropical rainforest in Costa Rica, where wind events are infrequent. We instrumented nests with thermocouples and flow-through CO₂ sensing chambers. The results showed that CO₂ concentrations exiting leaf-cutter ant nests follow a diel pattern with higher values at night. We developed an efflux model based on pressure differences that evaluated the observed CO₂ diel pattern in terms of ventilation by (1) free convection (warm, less dense air rises out the nest more prominently at night) and (2) episodic wind-forced convection events providing occasional supplemental ventilation during daytime. Average greenhouse gas emissions were estimated through nest vents at about 78 kg CO₂eq nest^-1 year^-1. At the ecosystem level, leaf-cutter ant nest vents accounted for 0.2% to 1% of total rainforest soil emissions. In wet, clayey tropical soils, leaf-cutter ant nests act as free convection-driven conduits for exporting CO₂ and other greenhouse gases produced within the nest (fungus and ant respiration, refuse decay), and by roots and soil microbes surrounding the nest. This allows A. cephalotes nests to be ventilated without reliable wind conditions.

How the thermal environment shapes the structure of termite mounds

A computational model has been developed to predict the role of environment in the forms and functions of termite mounds. The proposed model considers the most relevant forces involved in the heat transfer process of termite mounds, while also reflecting their gas-exchange function. The method adopts a system configuration procedure to determine thermally optimized mound structures. The model successfully predicts the main architectural characteristics of typical Macrotermes michaelseni mounds for the environmental conditions they live in. The results indicate that the mound superstructure and internal condition strongly depend on the combined effect of environmental forces. It is noted that mounds being exposed to higher solar irradiances develop intricate lateral channels, inside, and taller and more pronounced spire tilt towards the Sun, outside. It is also found that the mounds' spire tilt angle depends on the geographical location, following the local average solar zenith angle for strong irradiances. Although wind does not influence the overall over-ground mound shape, it significantly affects the mound internal condition. The results of this study resonate with what is seen in nature. The proposed approach provides a broader view of the factors that are effective in the form and function of a naturally made structure.

Colorful Wall-Bricks with Superhydrophobic Surfaces for Enhanced Smart Indoor Humidity Control

Humidity-control materials have attracted increasing attention because of energy savings and smart regulation of indoor comforts. The current research is a successive work to face challenges, such as poor performance, limitations for large-scale production, and surface contamination. Here, we report a smart humidity-control wall-brick manufactured from sepiolite using CaCl₂ as an additive. Low-temperature sintering generated a super hygroscopic interior structure, and further silane modification produced bricks with superhydrophobic surfaces. These superhydrophobic surfaces can promote the moisture storage and prevent the CaCl₂ solution from leaking even after the surface is wiped 100 times. Meanwhile, the superhydrophobic surfaces make the wall-bricks easy to clean; also, these materials possess antifouling and antifungal properties. The 24 h and saturated moisture adsorption-desorption contents reached 630 and 1700 g·m^-2, respectively. Furthermore, a test was performed using model houses in a real environment, which indicates that the wall-bricks can narrow the daily indoor humidity fluctuations by more than 20% in both wet and dry seasons. The white wall-brick can also be dyed with different colors and thus shows promise for applications in interior decorations of houses.

The architectural design of smart ventilation and drainage systems in termite nests

Termite nests have been widely studied as effective examples for ventilation and thermoregulation. However, the mechanisms by which these properties are controlled by the microstructure of the outer walls remain unclear. Here, we combine multiscale X-ray imaging with three-dimensional flow field simulations to investigate the impact of the architectural design of nest walls on CO₂ exchange, heat transport and water drainage. We show that termites build outer walls that contain both small and percolating large pores at the microscale. The network of larger microscale pores enhances permeability by one to two orders of magnitude compared to the smaller pores alone, and it increases CO₂ diffusivity up to eight times. In addition, the pore network offers enhanced thermal insulation and allows quick drainage of rainwater, thereby restoring the ventilation and providing structural stability to the wet nest.

Morphogenesis of termite mounds

Several species of millimetric-sized termites across Africa, Asia, Australia, and South America collectively construct large, meter-sized, porous mound structures that serve to regulate mound temperature, humidity, and gas concentrations. These mounds display varied yet distinctive morphologies that range widely in size and shape. To explain this morphological diversity, we introduce a mathematical model that couples environmental physics to insect behavior: The advection and diffusion of heat and pheromones through a porous medium are modified by the mound geometry and, in turn, modify that geometry through a minimal characterization of termite behavior. Our model captures the range of naturally observed mound shapes in terms of a minimal set of dimensionless parameters and makes testable hypotheses for the response of mound morphology to external temperature oscillations and internal odors. Our approach also suggests mechanisms by which evolutionary changes in odor production rate and construction behavior coupled to simple physical laws can alter the characteristic mound morphology of termites.

Termite mound architecture regulates nest temperature and correlates with species identities of symbiotic fungi

Background

Large and complex mounds built by termites of the genus Macrotermes characterize many dry African landscapes, including the savannas, bushlands, and dry forests of the Tsavo Ecosystem in southern Kenya. The termites live in obligate symbiosis with filamentous fungi of the genus Termitomyces. The insects collect dead plant material from their environment and deposit it into their nests where indigestible cell wall compounds are effectively decomposed by the fungus. Above-ground mounds are built to enhance nest ventilation and to maintain nest interior microclimates favorable for fungal growth.

Objectives

In Tsavo Ecosystem two Macrotermes species associate with three different Termitomyces symbionts, always with a monoculture of one fungal species within each termite nest. As mound architecture differs considerably both between and within termite species we explored potential relationships between nest thermoregulatory strategies and species identity of fungal symbionts.

Methods

External dimensions were measured from 164 Macrotermes mounds and the cultivated Termitomyces species were identified by sequencing internal transcribed spacer (ITS) region of ribosomal DNA. We also recorded the annual temperature regimes of several termite mounds to determine relations between mound architecture and nest temperatures during different seasons.

Results

Mound architecture had a major effect on nest temperatures. Relatively cool temperatures were always recorded from large mounds with open ventilation systems, while the internal temperatures of mounds with closed ventilation systems and small mounds with open ventilation systems were consistently higher. The distribution of the three fungal symbionts in different mounds was not random, with one fungal species confined to “hot nests.”

Conclusions

Our results indicate that different Termitomyces species have different temperature requirements, and that one of the cultivated species is relatively intolerant of low temperatures. The dominant Macrotermes species in our study area can clearly modify its mound architecture to meet the thermal requirements of several different symbionts. However, a treacherous balance seems to exist between symbiont identity and mound architecture, as the maintenance of the thermophilic fungal species obviously requires reduced mound architecture that, in turn, leads to inadequate gas exchange. Hence, our study concludes that while the limited ventilation capacity of small mounds sets strict limits to insect colony growth, in this case, improving nest ventilation would invariable lead to excessively low nest temperatures, with negative consequences to the symbiotic fungus.

Ecology: Termite Patterning at Multiple Scales

A vast and ancient array of regularly spaced dirt mounds - the result of termite activities- has been discovered in Brazil. Might this inform our understanding of general mechanisms of spatial patterning at different scales?

Termite mounds mitigate half of termite methane emissions

Termites are responsible for ∼1 to 3% of global methane (CH₄) emissions. However, estimates of global termite CH₄ emissions span two orders of magnitude, suggesting that fundamental knowledge of CH₄ turnover processes in termite colonies is missing. In particular, there is little reliable information on the extent and location of microbial CH₄ oxidation in termite mounds. Here, we use a one-box model to unify three independent field methods-a gas-tracer test, an inhibitor approach, and a stable-isotope technique-and quantify CH₄ production, oxidation, and transport in three North Australian termite species with different feeding habits and mound architectures. We present systematic in situ evidence of widespread CH₄ oxidation in termite mounds, with 20 to 80% of termite-produced CH₄ being mitigated before emission to the atmosphere. Furthermore, closing the CH₄ mass balance in mounds allows us to estimate in situ termite biomass from CH₄ turnover, with mean biomass ranging between 22 and 86 g of termites per kilogram of mound for the three species. Field tests with excavated mounds show that the predominant location of CH₄ oxidation is either in the mound material or the soil beneath and is related to species-specific mound porosities. Regardless of termite species, however, our data and model suggest that the fraction of oxidized CH₄ (f _ox) remains well buffered due to links among consumption, oxidation, and transport processes via mound CH₄ concentration. The mean f _ox of 0.50 ± 0.11 (95% CI) from in situ measurements therefore presents a valid oxidation factor for future global estimates of termite CH₄ emissions.

Architecture, space and information in constructions built by humans and social insects: a conceptual review

The similarities between the structures built by social insects and by humans have led to a convergence of interests between biologists and architects. This new, de facto interdisciplinary community of scholars needs a common terminology and theoretical framework in which to ground its work. In this conceptually oriented review paper, we review the terms 'information', 'space' and 'architecture' to provide definitions that span biology and architecture. A framework is proposed on which interdisciplinary exchange may be better served, with the view that this will aid better cross-fertilization between disciplines, working in the areas of collective behaviour and analysis of the structures and edifices constructed by non-humans; and to facilitate how this area of study may better contribute to the field of architecture. We then use these definitions to discuss the informational content of constructions built by organisms and the influence these have on behaviour, and vice versa. We review how spatial constraints inform and influence interaction between an organism and its environment, and examine the reciprocity of space and information on construction and the behaviour of humans and social insects.This article is part of the theme issue 'Interdisciplinary approaches for uncovering the impacts of architecture on collective behaviour'.

Exploring nest structures of acorn dwelling ants with X-ray microtomography and surface-based three-dimensional visibility graph analysis

The physical spaces within which organisms live affect their biology and in many cases can be considered part of their extended phenotype. The nests of social insect societies have a fundamental impact on their ability to function as complex superorganisms. Ants in many species excavate elaborate subterranean nests, but others inhabit relatively small pre-formed cavities within rock crevices and hollow seeds. Temnothorax ants, which often nest within acorns, have become a model system for studying collective decision making. While these ants have demonstrated remarkable degrees of rationality and consistent precision with regard to their nest choices, never before has the fine scale internal architecture and spatial organization of their nests been investigated. We used X-ray microtomography to record high-resolution three-dimensional (3D) scans of Temnothorax colonies within their acorns. These data were then quantified using image segmentation and surface-based 3D visibility graph analysis, a new computational methodology for analysing spatial structures. The visibility graph analysis method integrates knowledge from the field of architecture with the empirical study of animal-built structures, thus providing the first methodological cross-disciplinary synergy of these two research areas. We found a surprisingly high surface area and degree of spatial heterogeneity within the acorn nests. Specific regions, such as those associated with the locations of queens and brood, were significantly more conducive to connectivity than others. From an architect's point of view, spatial analysis research has never focused on all-surface 3D movement, as we describe within ant nests. Therefore, we believe our approach will provide new methods for understanding both human design and the comparative biology of habitat spaces.This article is part of the theme issue 'Interdisciplinary approaches for uncovering the impacts of architecture on collective behaviour'.

The Drivers of Heuristic Optimization in Insect Object Manufacture and Use

Insects have small brains and heuristics or 'rules of thumb' are proposed here to be a good model for how insects optimize the objects they make and use. Generally, heuristics are thought to increase the speed of decision making by reducing the computational resources needed for making decisions. By corollary, heuristic decisions are also deemed to impose a compromise in decision accuracy. Using examples from object optimization behavior in insects, we will argue that heuristics do not inevitably imply a lower computational burden or lower decision accuracy. We also show that heuristic optimization may be driven by certain features of the optimization problem itself: the properties of the object being optimized, the biology of the insect, and the properties of the function being optimized. We also delineate the structural conditions under which heuristic optimization may achieve accuracy equivalent to or better than more fine-grained and onerous optimization methods.

Solar-powered ventilation of African termite mounds

How termite mounds function to facilitate climate control is still only partially understood. Recent experimental evidence in the mounds of a single species, the south Asian termite Odontotermes obesus, suggests that the daily oscillations of radiant heating associated with diurnal insolation patterns drive convective flow within them. How general this mechanism is remains unknown. To probe this, we consider the mounds of the African termite Macrotermes michaelseni, which thrives in a very different environment. By directly measuring air velocities and temperatures within the mound, we see that the overall mechanisms and patterns involved are similar to that in the south Asian species. However, there are also some notable differences between the physiology of these mounds associated with the temporal variations in radiant heating patterns and CO₂ dynamics. Because of the difference between direct radiant heating driven by the position of the sun in African conditions, and the more shaded south Asian environments, we see changes in the convective flows in the two types of mounds. Furthermore, we also see that the south Asian mounds show a significant overturning of stratified gases, once a day, while the African mounds have a relatively uniform concentration of CO₂ Overall, our observations show that despite these differences, termite architectures can harness periodic solar heating to drive ventilation inside them in very different environments, functioning as an external lung, with clear implications for human engineering.

Excavation and aggregation as organizing factors in de novo construction by mound-building termites

Termites construct complex mounds that are orders of magnitude larger than any individual and fulfil a variety of functional roles. Yet the processes through which these mounds are built, and by which the insects organize their efforts, remain poorly understood. The traditional understanding focuses on stigmergy, a form of indirect communication in which actions that change the environment provide cues that influence future work. Termite construction has long been thought to be organized via a putative 'cement pheromone': a chemical added to deposited soil that stimulates further deposition in the same area, thus creating a positive feedback loop whereby coherent structures are built up. To investigate the detailed mechanisms and behaviours through which termites self-organize the early stages of mound construction, we tracked the motion and behaviour of major workers from two Macrotermes species in experimental arenas. Rather than a construction process focused on accumulation of depositions, as models based on cement pheromone would suggest, our results indicated that the primary organizing mechanisms were based on excavation. Digging activity was focused on a small number of excavation sites, which in turn provided templates for soil deposition. This behaviour was mediated by a mechanism of aggregation, with termites being more likely to join in the work at an excavation site as the number of termites presently working at that site increased. Statistical analyses showed that this aggregation mechanism was a response to active digging, distinct from and unrelated to putative chemical cues that stimulate deposition. Agent-based simulations quantitatively supported the interpretation that the early stage of de novo construction is primarily organized by excavation and aggregation activity rather than by stigmergic deposition.

Collective behaviour and swarm intelligence in slime moulds

The study of collective behaviour aims to understand how individual-level behaviours can lead to complex group-level patterns. Collective behaviour has primarily been studied in animal groups such as colonies of insects, flocks of birds and schools of fish. Although less studied, collective behaviour also occurs in microorganisms. Here, we argue that slime moulds are powerful model systems for solving several outstanding questions in collective behaviour. In particular, slime mould may hold the key to linking individual-level mechanisms to colony-level behaviours. Using well-established principles of collective animal behaviour as a framework, we discuss the extent to which slime mould collectives are comparable to animal groups, and we highlight some potentially fruitful areas for future research.

Dynamic environments of fungus-farming termite mounds exert growth-modulating effects on fungal crop parasites

This study investigated for the first time the impact of the internal mound environment of fungus-growing termites on the growth of fungal crop parasites. Mounds of the termite Odontotermes obesus acted as (i) temperature and relative humidity (RH) 'stabilisers' showing dampened daily variation and (ii) 'extreme environments' exhibiting elevated RH and CO₂ levels, compared to the outside. Yet, internal temperatures exhibited seasonal dynamics as did daily and seasonal CO₂ levels. During in situ experiments under termite-excluded conditions within the mound, the growth of the crop parasite Pseudoxylaria was greater inside than outside the mound, i.e., Pseudoxylaria is 'termitariophilic'. Also, ex situ experiments on parasite isolates differing in growth rates and examined under controlled conditions in the absence of termites revealed a variable effect with fungal growth decreasing only under high CO₂ and low temperature conditions, reflecting the in situ parasite growth fluctuations. In essence, the parasite appears to be adapted to survive in the termite mound. Thus the mound microclimate does not inhibit the parasite but the dynamic environmental conditions of the mound affect its growth to varying extents. These results shed light on the impact of animal-engineered structures on parasite ecology, independent of any direct role of animal engineers.

Animal thermoregulation: a review of insulation, physiology and behaviour relevant to temperature control in buildings

Birds and mammals have evolved many thermal adaptations that are relevant to the bioinspired design of temperature control systems and energy management in buildings. Similar to many buildings, endothermic animals generate internal metabolic heat, are well insulated, regulate their temperature within set limits, modify microclimate and adjust thermal exchange with their environment. We review the major components of animal thermoregulation in endothermic birds and mammals that are pertinent to building engineering, in a world where climate is changing and reduction in energy use is needed. In animals, adjustment of insulation together with physiological and behavioural responses to changing environmental conditions fine-tune spatial and temporal regulation of body temperature, while also minimizing energy expenditure. These biological adaptations are characteristically flexible, allowing animals to alter their body temperatures to hourly, daily, or annual demands for energy. They exemplify how buildings could become more thermally reactive to meteorological fluctuations, capitalising on dynamic thermal materials and system properties. Based on this synthesis, we suggest that heat transfer modelling could be used to simulate these flexible biomimetic features and assess their success in reducing energy costs while maintaining thermal comfort for given building types.

Optimal construction of army ant living bridges

Integrating the costs and benefits of collective behaviors is a fundamental challenge to understanding the evolution of group living. These costs and benefits can rarely be quantified simultaneously due to the complexity of the interactions within the group, or even compared to each other because of the absence of common metrics between them. The construction of 'living bridges' by New World army ants - which they use to shorten their foraging trails - is a unique example of a collective behavior where costs and benefits have been experimentally measured and related to each other. As a result, it is possible to make quantitative predictions about when and how the behavior will be observed. In this paper, we extend a previous mathematical model of these costs and benefits to much broader domain of applicability. Specifically, we exhibit a procedure for analyzing the optimal formation, and final configuration, of army ant living bridges given a means to express the geometrical configuration of foraging path obstructions. Using this procedure, we provide experimentally testable predictions of the final bridge position, as well as the optimal formation process for certain cases, for a wide range of scenarios, which more closely resemble common terrain obstacles that ants encounter in nature. As such, our framework offers a rare benchmark for determining the evolutionary pressures governing the evolution of a naturally occurring collective animal behavior.

Underground anemotactic orientation in leaf-cutting ants: perception of airflow and experience-dependent choice of airflow direction during digging

Air exchange between the large nests of Atta vollenweideri leaf-cutting ants and the environment strongly relies on a passive, wind-induced ventilation mechanism. Air moves through nest tunnels and airflow direction depends on the location of the tunnel openings on the nest mound. We hypothesized that ants might use the direction of airflow along nest tunnels as orientation cue in the context of climate control, as digging workers might prefer to broaden or to close tunnels with inflowing or outflowing air in order to regulate nest ventilation. To investigate anemotactic orientation in Atta vollenweideri, we first tested the ants' ability to perceive air movements by confronting single workers with airflow stimuli in the range 0 to 20 cm/s. Workers responded to airflow velocities ≥ 2 cm/s, and the number of ants reacting to the stimulus increased with increasing airflow speed. Second, we asked whether digging workers use airflow direction as an orientation cue. Workers were exposed to either inflow or outflow of air while digging in the nest and could subsequently choose between two digging sites providing either inflow or outflow of air, respectively. Workers significantly chose the side with the same airflow direction they experienced before. When no airflow was present during initial digging, workers showed no preference for airflow directions. Workers developed preferences for airflow direction only after previous exposure to a given airflow direction. We suggest that experience-modified anemotaxis might help leaf-cutting ants spatially organize their digging activity inside the nest during tasks related to climate control.

Individual versus collective cognition in social insects

The concerted responses of eusocial insects to environmental stimuli are often referred to as collective cognition at the level of the colony. To achieve collective cognition, a group can draw on two different sources: individual cognition and the connectivity between individuals. Computation in neural networks, for example, is attributed more to sophisticated communication schemes than to the complexity of individual neurons. The case of social insects, however, can be expected to differ. This is because individual insects are cognitively capable units that are often able to process information that is directly relevant at the level of the colony. Furthermore, involved communication patterns seem difficult to implement in a group of insects as they lack a clear network structure. This review discusses links between the cognition of an individual insect and that of the colony. We provide examples for collective cognition whose sources span the full spectrum between amplification of individual insect cognition and emergent group-level processes.

When social behaviour is moulded in clay: on growth and form of social insect nests

The nests built by social insects are among the most complex structures produced by animal groups. They reveal the social behaviour of a colony and as such they potentially allow comparative studies. However, for a long time, research on nest architecture was hindered by the lack of technical tools allowing the visualisation of their complex 3D structures and the quantification of their properties. Several techniques, developed over the years, now make it possible to study the organisation of these nests and how they are built. Here, we review present knowledge of the mechanisms of nest construction, and how nest structure affects the behaviour of individual insects and the organisation of activities within a colony.

Building mud castles: a perspective from brick-laying termites

Animal constructions such as termite mounds have received scrutiny by architects, structural engineers, soil scientists and behavioural ecologists but their basic building blocks remain uncharacterized and the criteria used for material selection unexplored. By conducting controlled experiments on Odontotermes obesus termites, we characterize the building blocks of termite mounds and determine the key elements defining material choice and usage by these accomplished engineers. Using biocement and a self-organized process, termites fabricate, transport and assemble spherical unitary structures called boluses that have a bimodal size distribution, achieving an optimal packing solution for mound construction. Granular, hydrophilic, osmotically inactive, non-hygroscopic materials with surface roughness, rigidity and containing organic matter are the easiest to handle and are crucial determinants of mass transfer during mound construction. We suggest that these properties, along with optimal moisture availability, are important predictors of the global geographic distribution of termites.

Stigmergic construction and topochemical information shape ant nest architecture

The nests of social insects are not only impressive because of their sheer complexity but also because they are built from individuals whose work is not centrally coordinated. A key question is how groups of insects coordinate their building actions. Here, we use a combination of experimental and modeling approaches to investigate nest construction in the ant Lasius niger. We quantify the construction dynamics and the 3D structures built by ants. Then, we characterize individual behaviors and the interactions of ants with the structures they build. We show that two main interactions are involved in the coordination of building actions: (i) a stigmergic-based interaction that controls the amplification of depositions at some locations and is attributable to a pheromone added by ants to the building material; and (ii) a template-based interaction in which ants use their body size as a cue to control the height at which they start to build a roof from existing pillars. We then develop a 3D stochastic model based on these individual behaviors to analyze the effect of pheromone presence and strength on construction dynamics. We show that the model can quantitatively reproduce key features of construction dynamics, including a large-scale pattern of regularly spaced pillars, the formation and merging of caps over the pillars, and the remodeling of built structures. Finally, our model suggests that the lifetime of the pheromone is a highly influential parameter that controls the growth and form of nest architecture.