Web bling: do orb-weaver spiders (Araneae: Araneidae) hack firefly (Coleoptera: Lampyridae) mating signals?

Background/Question/Methods

Sexual signals are often open to detection and exploitation – a predation strategy that can influence the evolution of prey mating systems. The sexual signals of most fireflies (Coleoptera: Lampyridae) are bioluminescent flashes that may be vulnerable to exploitation by predators. Anecdotal evidence from multiple sources suggests that orb-weaver spiders (Araneae: Araneidae) may take advantage of prey firefly distress flashes to attract additional fireflies into their webs. This hypothesis has never been tested, however. We explored this understudied predator-prey system to determine 1) the prevalence of araneid predation of fireflies at Blandy Experimental Farm, a field station in the northern Shenandoah Valley (Boyce, VA), 2) whether there are distinct and consistent flashing patterns associated with web-caught fireflies, and 3) if ensnared firefly prey affect subsequent prey capture for orb-weavers (Neoscona spp). We systematically recorded the natural history of these interactions and conducted a field experiment to measure Neoscona success in relation to fireflies. We placed flashing and non-flashing fireflies into Neoscona webs and recorded all prey capture for 2 hours afterwards.

Results/Conclusions

At Blandy Farm, Photinus pyralis fireflies comprised between 29-88% of Neoscona prey, depending on habitat type. Photuris spp. fireflies were not significant prey for Neoscona. There are consistent, rhythmic flash patterns associated with predation, but there is interspecific and intraspecific variability which has not been previously noted. Two-thirds of web-caught P. pyralis flashed rhythmically; fireflies do not always flash rhythmically, or at all. In predation experiments, there was no significant effect of treatment on subsequent prey capture, suggesting that the presence of a flashing firefly in a web may not necessarily benefit Neoscona predators. Our study has laid a foundation for future work investigating putative firefly signal exploitation by orb-weavers and other spider predators. Lampyridae mating systems exhibit remarkable diversity – each species has a unique flash pattern – so we expect each prey species may interact with araneid predators differently.