I first became fascinated by the potential behavioural adaptations of the cave spiders in the genus Meta (family Tetragnathidae) back in 2016, which spurred an interest for subterranean biology in general and lead to a student project on Meta menardi in Creswell Crags in 2017 and a two-month research visit to the University of the Balearic Islands in 2018 to look at Majorcan cave spiders.
Together with my student, Daniel Simonsen, and my collaborator, Prof Carlos Juan, from the University of the Balearic Islands, I have written a review paper on the fascinating behaviour and ecology of the Meta genus. We know nothing of most of the 23 species in the genus, but relatively much research (albeit much of it somewhat anecdotal in nature) has been conducted on the European Meta spiders. In the paper, we identify three possible behavioural adaptations including a modification of the orb web by almost eliminating frame threads (good evidence for), off-web hunting given that non-flying prey is a stable part of their diet (limited evidence, although more so for a variant where the radii are used as trip wires), and a dispersal stage where the spider spends at least one instar building webs outside of caves (some evidence). We also suggests a number of avenues for promising future research on these spiders.
The review paper has now been published as an advanced online open access paper in Behaviour.
Hesselberg, T.; Simonsen, D. and Juan, C. (2019). Do cave orb spiders show unique behavioural adaptations to subterranean life? A review of the evidence. Behaviour, Advanced Online doi.org/10.1163/1568539X00003564
Abstract
Interest for subterranean biology has risen sharply in recent years due to the simplicity of the cave environment. However, most studies have focussed on morphology with few studies looking at behaviour. The cave orb spiders show some unique behavioural adaptations compared to other orb spiders, including rudimentary orb webs, off-web foraging and a complex life cycle with a surface phase. Here, we compare these behavioural adaptations in the European Meta menardi and Meta bourneti to similar behaviours in surface-dwelling orb spiders. We find that current data suggest (1) an extreme reduction in the number of frame threads, (2) evidence of capturing non-flying prey, but not necessarily evidence for off-web foraging and (3) dispersal through a surface-dwelling life stage, but with data lacking on the role of ballooning and their return to caves. We conclude that Meta spiders have potential as model organisms for studies on behavioural adaptations and flexibility.
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