Stridulation

The mechanism is typically that of one structure with a well-defined lip, ridge, or nodules (the "scraper" or plectrum) being moved across a finely-ridged surface (the "file" or stridulitrum—sometimes called the pars stridens) or vice versa, and vibrating as it does so, like the dragging of a phonograph needle across a vinyl record.

When disturbed, Theraphosa blondi, the Goliath tarantula, can produce a rather loud hissing noise by rubbing together the bristles on its legs.

[15] The anatomical parts used to produce sound are quite varied: the most common system is that seen in grasshoppers and many other insects, where a hind leg scraper is rubbed against the adjacent forewing (in beetles and true bugs the forewings are hardened); in crickets and katydids a file on one wing is rubbed by a scraper on the other wing; in longhorned beetles, the back edge of the pronotum scrapes against a file on the mesonotum; in various other beetles, the sound is produced by moving the head—up/down or side-to-side—while in others the abdominal tergites are rubbed against the elytra; in assassin bugs, the tip of the mouthparts scrapes along a ridged groove in the prosternum; in velvet ants the back edge of one abdominal tergite scrapes a file on the dorsal surface of the following tergite.

Stridulation in several of these examples is for attracting a mate, or as a form of territorial behaviour, but can also be a warning signal (acoustic aposematism, as in velvet ants and tarantulas).

They arrange their body into a series of parallel C-shaped (counterlooped) coils that they rub together to produce a sizzling sound, rather like water on a hot plate.