Vibratory communication in a black widow spider (Latrodectus hesperus): signal structure and signalling mechanisms

Abstract

Despite the ubiquity of web-borne vibratory communication among many web-building spiders, few empirical studies, to date, have quantified the characteristics and mechanisms of the signals involved. In this study, we used western black widow spider, Latrodectus hesperus , and examined male signal characteristics, signal production mechanisms and signal transmission efficacy on webs. It is not clear how vibrations are transmitted through the chaotic cobweb typical of this species and relatives, and previous work argued that L. hesperus courtship vibrations lacked structure. We videorecorded courtship and copulation behaviour, and used laser vibrometry to record and characterize web-borne vibrations. We examined signalling mechanisms using synchronous high-speed video and vibrometry recordings. Lastly, we examined signal transmission by measuring transfer functions between body movements and the resulting vibration signal. We found that males displayed three distinct signal types (abdominal tremulation, bounce and web plucks), each of which were generated by a different signal production mechanism. Our results also show that male bounces and web plucks may convey information about male size. Contrary to earlier work, we show that during the later phases of male–female interactions, males intermittently organize individual signal types into stereotyped sequential displays (‘structured signalling’). Moreover, despite the cobweb structure, transfer function analyses showed that female webs transmit male signals with high efficacy. These results suggest that vibratory communication in L. hesperus , previously classified as simple signallers, can comprise emergent forms of signal complexity and lay the foundation for future studies on this mode of communication in other web-dwelling species. • Black widow males produce three different vibration signals during courtship. • These signals can carry important information about male size. • Males display signal elements haphazardly during the early courtship phase. • During later stages, males combine signal elements into a stereotyped sequence.