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1 December 2009 Palpal urticating hairs in the tarantula Ephebopus: fine structure and mechanism of release
Rainer Foelix, Bastian Rast, Bruno Erb
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The tarantula genus Ephebopus is exceptional with respect to its urticating hairs: they are located on the palps rather than on the abdomen, as is the rule for other Neotropical tarantulas. These urticating hairs occupy a small field of 1–2 mm2 on the medial side of the palpal femora. Each urticating hair measures 500–600 µm in length and 5–6 µm in diameter. Almost the entire hair shaft is studded with little barbs that point toward the hair tip. Urticating hairs arise from a slipper-shaped socket in the cuticle, at an angle of 25–30°. When the spider is threatened, it shows a brief palpal flick as a defensive reaction, whereby many urticating hairs are brushed off and fly through the air. These hairs do not have a preformed breaking point but become detached at the very base and are then pulled out from their sockets, like an arrow from a quiver. The actual release behavior occurs too quickly (0.1 s) to be followed by the naked eye. Video film analyses reveal that a single upward movement of the palps rubbing against the lateral surfaces of the spread chelicerae causes the dispersal of urticating hairs into the air.

Rainer Foelix, Bastian Rast, and Bruno Erb "Palpal urticating hairs in the tarantula Ephebopus: fine structure and mechanism of release," The Journal of Arachnology 37(3), 292-298, (1 December 2009).
Received: 28 December 2008; Published: 1 December 2009
defensive behavior
Neotropical tarantulas
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