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Bug word of the day — “Setae”

Today’s Bug Word of the Day is “setae” (pronounced “SEE-tee.”)

Setae is the plural version of the seldom-seen singular word seta (“SEE-tuh.”)

Setae are bristle-like hairs found on many insects and other arthropods.

The bristles you see on fuzzy caterpillars are setae, as are the bristles on “hairy” spiders such as tarantulas.

Chemically, setae have little in common with the hairs found on mammals. Setae are composed of chitin, the same complex sugar that’s a building block of arthropod exoskeletons.

Setae can be useful in several ways.

They can transmit environmental information to their owner, such as wind speed. They can aid in proprioception, which is the insect’s understanding of its

body positioning in space. In stinging caterpillars, setae are part of a defense strategy and can deliver an irritating toxin when animals touch the setae.

Matter of fact, the setae on some caterpillars can cause an allergic reaction in people, as you’ll see in this news release about tussock moth caterpillars. And the setae on Eastern tent caterpillars can cause pregnant mares to miscarry, if the mares happen to accidentally ingest the caterpillars while grazing, as described here.

And, of course, setae play a large role in arthropod coloration and appearance.