Beautifully intricate but lethal spider webs are an integral part of terrestrial arthropod ecosystems. But how old is this specialized and unique mode of predation? Arthropods trapped in spider silk webs have, in fact, been recovered from Early Cretaceous amber (Fig. 14.17). Enrique Penalver and his colleagues (2006) have illustrated a remarkable mosaic of silk strands, some with sticky droplets, which ambushed a fly and a mite, whereas another piece of amber shows a trapped wasp. The webs were elastic and armed with glue droplets - no match for stray insects. Preservation of spider silk in Lower Cretaceous amber from the Lebanon and from Spain suggests this form of predation was already well established by the Cretaceous. The diversification of the insects during the later Meso-zoic was tracked by a similar diversification in spiders; perhaps the evolution of aerial webs and winged insects was linked, evidence of an arms race in the airways of the Cretaceous.
legs. The opisthosoma usually has 12 segments. Arachnids breathe mainly through so-called book lungs or tracheae or both.
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