Friday Fellow: Truncate Trapdoor Spider

by Piter Kehoma Boll

Today I’m bringing you a species that fascinates me and that I was willing to introduce for a while. Unfortunately, there isn’t much information available about it, that being the reason for my delay in showing it here. However, as new information seems unlikely to appear soon, I can only show it with whatever is avaible.

Named Cyclocosmia truncata, today’s fellow is a trapdoor spider found in the East of the United States and sometimes referred to as truncate trapdoor spider. As all trapdoor spiders, it is a mygalomorph spider, such as tarantulas, and lives in a tunnel that it burrows in the ground and that is covered by a trapdoor. Trapdoor spiders in general rarely leave their burrows and hunt prey at night by standing behind the closed trapdoor and waiting for a prey to pass nearby, then jumping out and capturing it.

A truncate trapdoor spider in southeastern United States. Photo by iNaturalist user jimstarrett.*

Because trapdoor spiders are highly sedentary, they are very vulnerable to predators and parasites that can easily find them by locating their burrows. Species in the genus Cyclocosma have developed a fascinating morphological adaptation to cope with that. Their abdomen is abruptly truncated, giving the impression that someone just cut half of the abdomen off. This region of the abdomen is covered by a heavily sclerotized disc. When the spider is not active, it enters its burrow head first and the sclerotized disc fits perfectly to the walls of the tunnel, forming a false bottom that is impenetrable.

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A nice view of the peculiar disc of Cyclocosmia truncata. Author unknown. Photo taken from imgur.com

Not much more is known about the truncate trapdoor spider or its close relatives. They seem to be considerably rare, living in very restrict habitats, and their burrows are so well hidden that it is hard to find them in the wild.

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References:

Gertsch, W. J.; Platnick, N. I. (1975) A revision of the trapdoor spider genus Cyclocosmia (Aranae, Ctenizidae). American Museum Novitates 2580: 1–20.

Hunt, R. H. 1976. Notes on the ecology of Cyclocosmia truncata (Aranae, Ctenizidae) in Georgia. Journal of Arachnology 3: 83–86.

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*Creative Commons License
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

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Filed under Arachnids, Friday Fellow, Zoology

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