Abstract
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.
Highlights
Widespread arachnophobia [1,2] is fuelled, in part, by fear of the few neurotoxic spiders [3,4]
In parallel experiments 5–8, semiochemicals deposited by M. rubra had a significant deterrent effect on S. grossa (Exp. 5: 4 versus 17; p = 0.007, figure 3), L. hesperus (Exp. 6: 5 versus 14; p = 0.042, figure 3) and E. agrestis (Exp. 7: 4 versus 18; p = 0.007, figure 3), but not on A. diadematus (Exp. 8: 6 versus 13; p = 0.084, figure 3)
The amount of semiochemicals deposited by 111 M. rubra had a deterrent effect on S. grossa (Exp. 10: 5 versus 15, p = 0.041, figure 4) but the aversion effect caused by deposits of only 37 M. rubra was not statistically significant in this particular experiment (Exp. 9: 8 versus 15; p = 0.105, figure 4)
Summary
Widespread arachnophobia [1,2] is fuelled, in part, by fear of the few neurotoxic spiders [3,4]. This fear has inspired the development of tactics to physically and chemically discourage synanthropic spiders from settling in and around human dwellings [5]. Chemical tactics such as insecticide applications [5] are largely ineffective because spiders 2 can avoid insecticides by abandoning their web and rebuilding one elsewhere [3,6]. There is no immediate ecological reason why these materials are repellent to spiders
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