As part of the Oxford University Press John Fell Fund funded project on behavioural adaptations in the cave orb spider (Meta menardi), the MBIOL student, Emily Brannigan, and myself were lucky enough to observe some opportunistic foraging attempts by a female M. menardi when conducting research in the caves at Creswell Crags in August 2024. We observed the female responding to both a walking centipede and to another walking cave spider by leaving the hub of her web and rush along a radii towards the walking centipede/spider on the cave wall. These observations lend support to the radius tripwire hypothesis, which states that the unique geometry of the webs of the cave spider (i.e. that they have a reduced number of frame threads with radii attaching directly to the cave wall) are adaptations to facilitate the capture of walking prey (by the walking prey bumping in to the radius attaching to the wall and thereby alerting (via vibrations transmitted through the radial threads) the resident spider of the prey allowing it to rush out and overpower the prey (although in both our observations the prey capture was not successful, possibly because the resident spider aborted her attack when she realised that the prey was as large and dangerous as herself…).
We deemed these observations so interesting (and had the luck that we managed to record them on a video camera and a phone) that we decided to published detailed accounts and analyses of them. Our resulting short behavioural note has now been published in the journal Ethology.
Hesselberg, T. and Brannigan, E. (2025). Prey Capture Outside of the Web? Observational Evidence of a Novel Form of Prey Capture in a Cave Orb Web Spider. Ethology, Early View. https://doi.org/10.1111/eth.13563
Abstract
The European cave spider (Meta menardi) builds orb webs in the entrance and twilight zone of caves. However, the scarcity of flying prey inside caves means that only about half of its diet consists of flying insects, with walking prey making up the remaining half. The capture of non-flying prey is not generally known from aboveground orb web building spiders, which exclusively capture flying prey in their webs. It is currently a mystery how the cave spider manages to capture prey walking on the cave wall. A number of hypotheses have been suggested, including that the spider leaves its web completely (the off-web hunting hypothesis), that walking prey slips on the smooth cave ceiling and falls into the horizontally inclined webs (the prey slip hypothesis) or that the unique geometry of the cave spider’s orb web, which lacks frame threads, means that the radii that attach directly to the cave wall are used as tripwires to alert the spider of passing prey (the radius tripwire hypothesis). Here we report on three in situ observations of M. menardi responding to radius stimulation from artificial and walking prey by running towards the cave wall. Although the opportunistic observations of responses to real prey both involved potentially dangerous prey (a centipede and another large M. menardi) and were unsuccessful prey capture events, the clear response to walking prey nonetheless constitutes the first strong observational evidence in support of the radius tripwire hypothesis.
Recent Comments