Tail vibration

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Tail vibration is when snakes shake their tails quickly as a defensive response to a threat. It’s different from caudal luring, where a snake wags its tail to attract prey.

Rattlesnakes are the most famous tail-vibrators, but many other snakes in the Colubridae and Viperidae families also vibrate their tails. Some other groups, and even a lizard species (Takydromus tachydromoides), do it as well.

Rattlesnakes hold their tails upright while vibrating because their rattle makes sound. Other snakes vibrate against the ground or objects. The speed of tail vibration depends on temperature: warmer snakes shake faster. Rattlesnakes can reach up to about 90 vibrations per second, making it one of the fastest movements in vertebrates. This relies on special muscles at the tail tip.

Across many snakes, vibration speeds vary. In a study of 155 snakes from 56 species, speeds ranged from about 9 to 91 vibrations per second. Some non-rattlesnakes can reach around 50 per second, but the fastest speeds are typical of rattlesnakes.

Why snakes vibrate their tails isn’t fully known. The main ideas are:
- It could be a warning sound to deter predators (an auditory signal).
- It might distract a predator from the head, focusing attention on the tail.
- Nonvenomous snakes near rattlesnakes may mimic the rattling to gain protection (a Batesian mimicry effect).

There is some evidence for mimicry in gophersnakes, which tail-vibrate longer in areas where rattlesnakes are common. But tail vibration also occurs in Old World venomous snakes, so mimicry isn’t the whole story.

Tail vibration seems to be an ancient behavior in vipers and colubrids and may have helped lead to the evolution of the rattling sound. Some scientists think the rattle started as a way to enhance tail-luring or as a loose version of tail vibration that eventually became a specialized structure. The exact evolutionary path is still debated.