Silk and the earliest spiders

Article By:

Selden, Paul A. Paleontological Institute, University of Kansas, Lawrence, Kansas.

Last reviewed:2010

DOI:https://doi.org/10.1036/1097-8542.YB100140

Spiders are familiar animals whose intricate webs have been marveled at by humans for thousands of years. Silk production is not unique to spiders; indeed, silk is made by arthropods as diverse as silkworms, the spectacular glowworms of New Zealand, and other arachnids including pseudoscorpions. All spiders produce silk, and the possession of silk glands in the abdomen (opisthosoma) is a characteristic feature of the arachnid order Araneae. Other characters of spiders include venom glands in the forepart of the body (prosoma), which emerge from a pore in the cheliceral fang, and the presence of hairless fangs separates spiders from closely related arachnids such as Amblypygi (tailless whip scorpions). During spider evolution, not all of these characters appeared at the same time. For example, the most primitive living spiders, members of the suborder Mesothelae, lack venom glands and hence have no pore in the fang. All other spiders (the suborder Opisthothelae) possess venom glands, except rarely when they have been secondarily lost. New evidence from 380-million-year-old fossil spiderlike animals shows that they lacked venom glands. However, like true spiders, they had silk glands and spigots. The weaving apparatus was different, though, and thus we can speculate on how the silk was used. Arachnologists can now see more clearly the evolutionary pathway of silk production and silk use in early arachnids.

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