Statistical calculations (R Code) from 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, <i>Myrmica rubra,</i> black garden ants, <i>Lasius niger,</i> or western carpenter ants, <i>Camponotus modoc</i>, and then offered select urban spiders in 3-chamber olfactometer bioassays a choice between ant-exposed filter paper and unexposed control filter paper. Semiochemical deposits of <i>M. rubra</i>, but not of <i>L. niger</i> or <i>C. modoc</i>, had a significant deterrent effect on subadults of the false black widow, <i>Steatoda grossa,</i> the black widow, <i>Latrodectus hesperus</i>, and the hobo spider, <i>Eratigena agrestis,</i> as well as a moderate (but statistically not significant) deterrent effect on the cross spider, <i>Araneus diadematus</i>. The deterrent effect caused by semiochemical deposits of <i>M. rubra</i> may be attributable to the aggressive nature and efficient foraging of <i>M. rubra</i> in its invaded North American range, exerting selection pressure on community members to recognize <i>M. rubra</i> semiochemicals and to avoid micro-locations occupied by <i>M. rubra</i>.