Last week I participated in the 24th International Conference on Subterranean Biology, which took place in Aveiro Portugal. The conference was very well organised and full of interesting talks about a range of cave and subterranean organisms. In the past few years, I have been more and more intrigued by the behaviour and webs of the few cave orb spiders in the genus Meta.
At the conference, I gave a talk on some of the alleged behavioural adaptations to cave life found in these spiders (modified and reduced orb webs, and potential off-web hunting) as well as their interesting life cycle, which includes an instar spent outside of caves. The abstract of my talk was.
Given the low abundance of flying insects in subterranean habitats, it is surprising that troglophile orb spiders in the genus Meta (family Tetragnathidae) are relatively abundant in subterranean habitats, especially in the twilight zone of European caves. As is the case for most subterranean invertebrates, we know very little about their behaviour. However, they have been reported to possess a number of specific behavioural adaptations to the cave environment. These include modifications of the traditional orb web such that webs do not have frame and anchor threads, but instead have the radii (the spokes in the web) attaching directly to the cave walls, and that cave spiders, unlike epigean orb spiders, allegedly engage in off-web foraging as well as on-web foraging. Here I review the evidence for these claims and compare these to the behaviour of epigean spiders in the related Metellina genus including preliminary comparative data on both morphology and web characteristics. In addition, I will discuss the potential of using the cave Meta spiders, especially M. menardi and M. bourneti, as model organisms for studying search behaviour, mate finding behaviour and sexual selection, as these spiders show an interesting life cycle with young instars leaving the cave environment to spend an instar in the epigean environment before returning. It is currently not known how spiderlings locate subterranean habitats, how males find female webs or whether the level of sexual selection is lower in the resource-limited subterranean habitat compared to the epigean habitat.
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