Spider behaviours increase trap efficacy

Abstract

Orb-weaving spiders often use their legs to briefly jerk the radii of the web, generating intense vibrations throughout the web. Several functions have been proposed for this behaviour, but there is a lack of empirical evidence. In this study, we conducted a series of experiments on Cyclosa argenteoalba to examine the function and adaptive significance of spider jerks in the context of interactions with prey. First, we used within-individual, inter-individual, and interspecific comparisons (in three co-occurring Cyclosa sp.) to test whether the relation between prey and spider size predict the frequency of jerks that the spider performs. Second, we examined whether jerks prevent prey from escaping the web, whether jerks entangled more spiral threads around the prey, and how prey size affected this result. We found that spiders jerked more as the prey size increased and as spider size decreased. Jerking behaviour reduced the probability of prey escaping from the web and increased the number of spiral threads contacting the prey. The jerk efficiency (the number of additional spiral threads contacted per jerk) was lower in larger prey, which potentially explains why spiders jerk more towards larger prey. Collectively, our results highlight size dependency in the performance of jerks and their role in prey capture. Significance statements Many orb-weaving spiders show a behaviour that pulls the radii of the web intensively using their legs towards their prey, called jerks. Though this behaviour is common and has been recognised for many decades, the function and their adaptive significance have been surprisingly understudied. Using a series of experiments, we demonstrate that jerks help spiders prevent prey escape and subdue prey by entangling additional spiral (sticky) threads around the prey. We further show that the performance of jerks is size-dependent: spiders jerk more (1) as their size decreases and (2) as prey size increases. Further in-depth analysis suggests that the observed size-dependent jerks seem to be related to spiders' cautiousness and/or reduced jerk efficiency towards larger prey.