Last autumn, I was a visiting professor at the University of the Balearic Islands in Mallorca for two months, and while I didn’t find any of the Meta bourneti cave spiders, I originally wanted to study, I did manage to find multiple Metellina merianae spiders in several of the caves I visited. The findings have now been published in an article in Subterranean Biology, where I compare the geometry of the webs and the morphology of the spiders with the closely related wood inhabiting Metellina mengei. Data from the latter species was collected by the undergraduate student Daniel Simonsen, who is also a co-author on the paper. When controlling for differences in size, we did not find any large overall differences, and concludes that Metellina merianae, which can also be found in terrestrial habitats, has not (yet?) evolved any morphological or behavioural adaptations to subterranean life.
Hesselberg, T. and Simonse, D. (2019). A comparison of morphology and web geometry between hypogean and epigean species of Metellina orb spiders (family Tetragnathidae). Subterranean Biology 32, 1-13.
DOI: 10.3897/subtbiol.31.36222
Abstract
Studies on the behaviour of subterranean animals are rare, mainly due to the problems with collecting data in these inaccessible habitats. Web-building cave spiders, however, leave a semi-permanent record of their foraging behaviour, which can relatively easily be recorded. In this study, we compare size, leg lengths and web characteristics between hypogean populations of Metellina merianae with its close wood-inhabiting relative M. mengei. We confirm previous observations that M. merianae does not show any obvious morphological and behavioural adaptions to a subterranean life-style, although individuals of the cave species were significantly larger and had webs with relatively fewer radii and capture spiral turns than M. mengei. We were, however, not able to determine if these findings indicate a transition towards behavioural adaptation to caves or if they are a result of behavioural flexibility in response to the different humidity and temperature between caves and woodland. Finally, we did not find any effect of cave characteristics on either the number of radii or the area of the M. merianae web.
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