杏吧原创

You鈥檇 think a nimble stinger and powerful pincers would be enough. But some scorpions have another defensive strategy: hissing.

Few recordings exist of scorpions hissing. But now the evolution of the behavior has been traced.

Arachnologist at the California Academy of Sciences in San Francisco and her colleagues used DNA sequencing and physical comparisons to work out the evolutionary history of a subfamily of scorpions called the Centruroidinae. In doing so, they discovered how some members evolved sound-producing organs.

The family includes the club-tailed scorpions: medium-sized arachnids that live all over the Americas. 鈥淭heir tails are powerful and they pack a pretty substantial sting,鈥� says Esposito.

These are the only scorpions from the Americas known to make a noise. Esposito likens the sound to that of a wind-up toy.

A work of friction

It鈥檚 generally thought that a scorpion鈥檚 hiss acts as a defensive warning, similar to a rattlesnake鈥檚 rattle. Like other arachnids, scorpions hear acoustic signals as ground-based vibrations through their feet. But hisses are sent through the air, which is how mammals 鈥� scorpions鈥� primary predators 鈥� hear sounds.

Club-tailed scorpions by rubbing a comb-like structure on the underside of their bodies against a plate of exoskeleton on their bellies, which is covered in fine granules, like sandpaper.

This is also how bowed-stringed instruments like the violin work: the bow cyclically sticks and slips over the string to generate vibrations. The player can control the string鈥檚 vibrations by varying the frictional forces between bow and string.

In the sea, .

鈥淚f we can confirm that these scorpions are indeed using this mechanism, it would be the first example of biological sound production on land using stick-slip friction,鈥� says Esposito.

Based on the family tree they constructed, Esposito and her colleagues concluded that the ability to hiss evolved once and some species later lost it.

There also seems to be a pattern shaping which scorpions became mute. 鈥淚t appears that those in the extremely toxic group have lost the ability to hiss over time, whereas the group that delivers a sting that鈥檚 painful but not necessarily lethal has retained the ability to hiss,鈥� says Esposito.

If that鈥檚 true, it means the most terrifying-sounding scorpions may be more bark than bite, while their more venomous cousins are so secure in their toxicity that they don鈥檛 need to boast.