Masaki Hoso, a researcher at the Naturalis Biodiversity Center in the Netherlands found that in a move reminiscent of certain lizards that can voluntarily detach their tails, young Satsuma caliginosa snails self-amputate their foot when attacked by their nemesis, the Pareas iwasakii snake.
S caliginosa is a brown-shelled land snail that lives on the Japanese islands of Ishigaki, Iriomote and Yonaguni.
Adult S caliginosa have shells with armoured openings. The hole from which the mollusc's body emerges is built up with extra material, making it tough for snakes to extract the snail once it retracts inside, the Livescience reported.
Young snails can't build up this extra armour because they have to finish growing their shell to maturity first. That leaves them vulnerable to snail-eating P iwasakii snake, so instead a young snail will sacrifice its foot to an attacking snake.
The foot is the part of the body that the snail uses to get around; it looks more like a tail slithering along the ground than an actual foot.
Hoso combined field observations of snails with laboratory experiments in which he exposed the them to snakes.
He found that about 60 per cent of snails survive snake attacks, about half of them by pulling away from the snakes' needle-sharp teeth.
However in 45.4 per cent of cases, the snails self-amputated their feet.
Older snails were less likely to drop their foot than younger snails, probably because self-amputation is a costly adaption: It takes snails about a month to regrow the lost foot.
Hoso was able to recapture more snails with regrown feet in the wild than snails with original feet, suggesting that self-amputation doesn't increase the snails' death rate in the long run.
The study was published in the journal Proceedings of the Royal Society B.