Evidence of bird dropping masquerading by a spider to avoid predators

Conspicuous cruciform silk decorations deflect avian predator attacks

Although camouflage as an effective antipredator defence strategy is widespread across animals, highly conspicuous color patterning is not uncommon either. Many orb-web spiders adorn their webs with extra, bright white silk. These conspicuous decorations are hypothesized to deter predators by warning the presence of sticky webs, camouflaging spiders, acting as a decoy, or intimidating predators by their apparent size. The decorations may also deflect predator attacks from spiders. However, empirical evidence for this deflection function remains limited. Here we tested this hypothesis using the X-shaped silk cruciform decorations built by females of Argiope minuta. We employed visual modelling to quantify the conspicuousness of spiders and decorations from a perspective of avian predators. Then we determined actual predation risk on spiders using naïve chicks as predators. Spider bodies and decorations were conspicuous against natural backgrounds to the avian visual systems. Chicks attacked the spider main bodies significantly less frequently on the decorated webs than on the undecorated webs, thus reducing predation risk. When both spiders and decorations were present, chicks also attacked the spider main bodies and their legs or decorations, and not randomly: they attacked the legs or decorations sooner and more frequently than they attacked the main bodies, independence of the ratio of the surface area between the decoration and spider size. Despite the increase in detectability, incorporating a conspicuous cruciform decoration to the web effectively defends the spider by diverting the attack towards the decoration or leg, but not by camouflaging or intimidating, thus, supporting the deflection hypothesis. This article is protected by copyright. All rights reserved.

Discoid decorations function to shield juvenile Argiope spiders from avian predator attacks

Decorating behavior is common in various animal taxa and serves a variety of functions from camouflage to communication. One predominant function cited for decoration is to avoid predators. Conspicuous, disc-like (discoid) silk decorations spun by orb-web Argiope juvenile spiders are hypothesized, among others, to defend spiders against visual predators by concealing spider outlines on the web, deflecting attacks, shielding them from view, or masquerading as bird-droppings. However, the direct evidence is limited for a specific mechanism by which discoid decorations may deter predators. Here we evaluate the mechanisms by which discoid decorations may defend Argiope juveniles against naïve chicks. Using visual modeling, we show that avian predators are able to distinguish spiders from discoid decorations. Using chick predation experiments, we found that the naïve chicks readily pecked any objects, ruling out the possibility of their neophobia. Significantly more chicks attacked spiders when they were exposed to chicks, regardless of whether their webs had discoid decorations, but few chicks attacked spiders when they were behind the decorations. We also found that significantly few chicks attacked decorations when spiders were absent or behind the decorations. We thus conclude that discoid decorations function to deter avian predators by shielding the spider from view or distracting, not by deflecting attacks, concealing the spider’s outline, or masquerading as bird-droppings. This study sheds light on the study of other similar anti-predator strategies, in a wide range of spider species and other animals that use decorating strategies.

The antipredator benefits of postural camouflage in peppered moth caterpillars

Camouflage is the most common form of antipredator defense, and is a textbook example of natural selection. How animals’ appearances prevent detection or recognition is well studied, but the role of prey behavior has received much less attention. Here we report a series of experiments with twig-mimicking larvae of the American peppered moth Biston betularia that test the long-held view that prey have evolved postures that enhance their camouflage, and establish how food availability and ambient temperature affect these postures. We found that predators took longer to attack larvae that were resting in a twig-like posture than larvae resting flat against a branch. Larvae that were chilled or food restricted (manipulations intended to energetically stress larvae) adopted a less twig-like posture than larvae that were fed ad libitum. Our findings provide clear evidence that animals gain antipredator benefits from postural camouflage, and suggest that benefits may come at an energetic cost that animals are unwilling or unable to pay under some conditions.

Color lures in orb-weaving spiders: a meta-analysis

Lures are deceptive strategies that exploit sensory biases in prey, usually mimicking a prey’s mate or food item. Several predators exploit plant–pollinator systems, where visual signals are an essential part of interspecific interactions. Many diurnal, and even nocturnal, orb-web spiders present conspicuous body coloration or bright color patches. These bright colors are regarded as color-based lures that exploit biases present in insect visual systems, possibly mimicking flower colors. The prey attraction hypothesis was proposed more than 20 years ago to explain orb-web spider coloration. Although most data gathered so far has corroborated the predictions of the prey attraction hypothesis, there are several studies that refute these predictions. We conducted a multilevel phylogenetic meta-analysis to assess the magnitude of the effect of conspicuous orb-web spider body coloration on prey attraction. We found a positive effect in favor of the prey attraction hypothesis; however, there was substantial heterogeneity between studies. Experimental designs comparing conspicuous spiders to painted spiders or empty webs did not explain between-studies heterogeneity. The lack of theoretical explanation behind the prey attraction hypothesis makes it challenging to address which components influence prey attraction. Future studies could evaluate whether color is part of a multicomponent signal and test alternative hypotheses for the evolution of spider colors, such as predator avoidance and thermoregulation.

Chewing Holes for Camouflage

Camouflaged objects are harder to detect if the background itself is more heterogeneous, and search becomes increasingly inefficient when the scene contains multiple items resembling the target. Some adult leaf beetles (Coleoptera: Chrysomelidae) with highly specialized habits make holes on host plant leaves while feeding. We propose that leaf beetles camouflage themselves with their feeding holes. The presence of holes makes predators' visual search harder, thus giving beetles more time to escape from the leaf surface either by jumping (Galerucinae: Alticini) or rolling (rest of Chrysomelidae). Based on behavioral observations and analysis of 25 photographs of feeding leaf beetles (15 species), we demonstrate that adult leaf beetles camouflage themselves by creating holes of uniform size, approximately half of the beetle body size. Observation of the feeding behavior and anatomy of a typical hole-feeding beetle (Altica cirsicola) showed that the foregut volume and head-prothorax mobility of beetles are the two major factors that constrain the hole size. A computer-simulated visual search test showed that the greater the number of holes, and the more each hole approached beetle body size, the longer it took humans (as models) to locate a beetle on a leaf. This study reports a newly discovered kind of camouflage, hole-feeding camouflage, in leaf beetles, which makes visual detection or recognition more difficult by changing the environmental background. This type of camouflage may open up a range of new possibilities for studies in animal cognition analysis and evolution of anti-predation defenses.

Record breaking achievements by spiders and the scientists who study them

Organismal biology has been steadily losing fashion in both formal education and scientific research. Simultaneous with this is an observable decrease in the connection between humans, their environment, and the organisms with which they share the planet. Nonetheless, we propose that organismal biology can facilitate scientific observation, discovery, research, and engagement, especially when the organisms of focus are ubiquitous and charismatic animals such as spiders. Despite being often feared, spiders are mysterious and intriguing, offering a useful foundation for the effective teaching and learning of scientific concepts and processes. In order to provide an entryway for teachers and students-as well as scientists themselves-into the biology of spiders, we compiled a list of 99 record breaking achievements by spiders (the "Spider World Records"). We chose a world-record style format, as this is known to be an effective way to intrigue readers of all ages. We highlighted, for example, the largest and smallest spiders, the largest prey eaten, the fastest runners, the highest fliers, the species with the longest sperm, the most venomous species, and many more. We hope that our compilation will inspire science educators to embrace the biology of spiders as a resource that engages students in science learning. By making these achievements accessible to non-arachnologists and arachnologists alike, we suggest that they could be used: (i) by educators to draw in students for science education, (ii) to highlight gaps in current organismal knowledge, and (iii) to suggest novel avenues for future research efforts. Our contribution is not meant to be comprehensive, but aims to raise public awareness on spiders, while also providing an initial database of their record breaking achievements.