Natural Compounds as Spider Repellents: Fact or Myth?

Attraction or Repelling Effects of Commercial Plant Essential Oils on the Synanthropic Cheiracanthium mildei (Araneae: Cheiracanthiidae)

The northern yellow sac spider Cheiracanthium mildei L. Koch, is expanding its range to Central Europe, especially to synanthropic habitats. The spiders become unwanted companions because of the unreasonable fear - arachnophobia, and estetic reason - silk retreats in corners, capturing dust. The most commonly used substances against spiders are pesticides, which are, however, toxic. In our work we tested the attraction or repellence of 15 essential oils (EO) from plants representing eight families to C. mildei. Our research has shown a significant repellent effect of EO from three plants, namely Syzygium aromaticum (L.) Merr. et L. M. Perry (Myrtales: Myrtaceae), Ananas comosus (L.) Merr. (Poales: Bromeliaceae) and Musa sp. (L.) (Zingiberales: Musaceae). In contrast, some EOs appeared to have an attraction effect, particularly Carum carvi L. (Apiales: Apiaceae). Zingiber officinale Roscoe (Zingiberales: Zingiberaceae) reduced the tendency of spiders to construct the silken retreat. S. aromaticum, A. sativus, Musa sp. and Z. officinale have the potential to be used as natural repellents against spiders.

Pheromone communication among sexes of the garden cross spider Araneus diadematus

Chemical communication plays a fundamental role in many aspects of an animal’s life from assessing habitat quality to finding mating partners. Behavioural observations show that chemical communication likewise plays an important role in spiders, but the contexts and the substances involved are little explored. Here, we investigate the chemical communication in the garden cross spider Araneus diadematus (Clerck, 1757) between and within the sexes. Using choice trials, we demonstrate that males are attracted to odours of adult females, but not to those of subadult females. Our data further suggest that adult females avoid odours of conspecific adult females, possibly in order to reduce reproductive competition with other females. Cuticle and silk extracts as well as headspace samples of subadult and adult virgin females were analysed via GC–MS. Available candidate compounds for the female sex pheromone were tested via electroantennography on palps (electropalpography) of adult virgin females and on females in behavioural trials. We propose sulcatone (6-methyl-5-hepten-2-one) as a candidate substance for the female volatile pheromone and several long-chained alkanes and alcohols as candidates for contact pheromones. Apart from demonstrating that attraction of males to females depends on the latter’s developmental stage, our study suggests that pheromones can also play an important role between females, an aspect that requires further attention.

Know your foe: synanthropic spiders are deterred by semiochemicals of European fire ants

Many ants prey on spiders, suggesting that web-building spiders may avoid micro-locations near ant colonies or frequented by foraging ants. Here we tested the hypothesis that ant-derived semiochemicals deter synanthropic spiders. To generate stimuli, we exposed filter paper for 12 h to workers of European fire ants, Myrmica rubra, black garden ants, Lasius niger, or western carpenter ants, Camponotus modoc, and then offered select urban spiders in three-chamber olfactometer bioassays a choice between ant-exposed filter paper and unexposed control filter paper. Semiochemical deposits of M. rubra, but not of L. niger or C. modoc, had a significant deterrent effect on subadults of the false black widow, Steatoda grossa, the black widow, Latrodectus hesperus, and the hobo spider, Eratigena agrestis, as well as a moderate (but statistically not significant) deterrent effect on the cross spider, Araneus diadematus. The deterrent effect caused by semiochemical deposits of M. rubra may be attributable to the aggressive nature and efficient foraging of M. rubra in its invaded North American range, exerting selection pressure on community members to recognize M. rubra semiochemicals and to avoid micro-locations occupied by M. rubra.

Multimodal and multifunctional signaling? - Web reduction courtship behavior in a North American population of the false black widow spider

Males of widow spiders courting on the web of females engage in web-reduction behavior which entails excising a section of the web, bundling it up, and wrapping it with their silk. Males of the false black widow spider, Steatoda grossa, in European populations also produce stridulatory courtship sound which has not yet been studied in their invaded North American range. Working with a North American population of S. grossa, we tested the hypotheses that (1) web reduction by males renders webs less attractive to rival males; (2) deposition of silk by courting males has an inter-sexual (male-female) signal function that enhances their likelihood of copulation; and (3) stridulatory sound is a courtship signal of males. Testing anemotactic attraction of males in Y-tube olfactometer experiments revealed that reduced webs (indicative of a mated female) and intact webs (indicative of a virgin female) were equally attractive to males. Recording courtship behavior of males with either functional (silk-releasing) spinnerets or spinnerets experimentally occluded on the web of virgin females showed that males with functional spinnerets were more likely to copulate with the female they courted. Although males possess the stridulatory apparatus to produce courtship sound, they did not stridulate when courting or copulating on the web of females. Our data support the conclusion that web-reduction behavior of S. grossa males in their invaded North American range has no long-range effect on mate seeking males. Instead, web-reduction behavior has an inter-sexual signaling function that seems to be linked to functional spinnerets of the courting male. The signal produced by a male likely entails a volatile silk-borne pheromone, but may also embody a gauge of his endurance (the amount of time he engages in web reduction causing web vibrations).