Firefly flashing and jumping spider predation

Bioluminescent flashing in fireflies, while primarily a sexual signal, is known to deter some predators while attracting others. We tested whether flashing serves an antipredator function against two species of diurnal, visually hunting jumping spiders, Phidippus princeps and Phidippus audax. To confirm anecdotal reports that fireflies flash during the day in a nonmating context, we documented that adult fireflies (Photuris sp.) of both sexes flash when disturbed in daylight. We also confirmed that activity periods of Phidippus and fireflies overlap, and that spiders attack fireflies and elicit flashing behaviour. We conducted three experiments to examine the influence of flashing on spider behaviour. (1) We tested whether the sudden onset of a flashing LED startled spiders that had initiated attacks on crickets, and found no evidence that it did so. (2) We used choice tests to determine whether flashing lights attracted or deterred spiders from attacking palatable prey. Spiders more often attacked crickets positioned next to a flashing LED versus an LED that was either off or glowed steadily. (3) Many firefly species are distasteful. Therefore, we tested whether flashing lights facilitate avoidance of unpalatable prey with experience. Spiders were given seven encounters with unpalatable prey (nonluminescent Ellychnia corrusca fireflies) associated with either flashing or unlit LEDs. Spiders in the two treatments were equally likely to attack the prey during their first encounter, but spiders exposed to flashing LEDs were significantly less likely to attack unpalatable prey by their seventh trial. Spiders tested with palatable prey showed no decline in attacks after exposure to flashing LEDs. We conclude that, although bioluminescent flash signals may increase attack rates by predatory jumping spiders, they may also facilitate learning about unpalatable prey. Thus, the costs and benefits of flashing may depend on the prevalence of firefly palatability.