I have to admit right up front that the title of this article is not really accurate. No snakes chew their food the way we do. Almost all snakes must swallow their food whole, which limits their (often considerable) gape to items they can jaw-walk their kinetic skulls over. Taken as a whole, there are few animals on Earth that snakes do not eat -- whales and dolphins, elephants, animals endemic to the polar regions, some very toxic millipedes. There are snakes that swallow leopards whole, snakes that eat porcupines without removing the quills, snakes that tolerate stabs from catfish spines, snakes that eat other snakes longer than they are. Here's a video of a Tantilla eating a giant centipede. As a group, they can eat nearly anything. They all swallow their prey whole. Almost.
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| Except for this one |
Its genus name is
Fordonia, which is probably meaningless, seeing as it was biologist J.E. Gray of the British Museum of Natural History,"well known for inventing many apparently meaningless scientific names", who came up with it (he also named the North American
Farancia). Commonly known as the Crab-eating Water Snake or White-bellied Mangrove Snake (after the specific epithet),
Fordonia leucobalia is native to the mangrove swamps and tidal mud flats of southeast Asia and northern Australia. It lives in mud lobster and fiddler crab burrows, and moves by
jumping across the soft mud, into which it would sink if it tried to slither.
Part of a small but interesting group of live-bearing snakes known as
homalopsids,
Fordonia is southeast Asia's answer to the North American natricine
Nerodia, for many the archetypical semi-aquatic snake. What sets
Fordonia apart from other homalopsid snakes, which feed mostly on fishes, is that it eats crabs, an observation first made by Cantor in 1847. (This may be highly cathartic for the snakes, whose primary predators as juveniles include large crabs.)
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| Those are hard-shelled decapod crustaceans, for you biologists out there |
Like many other arthropods, crabs have an anti-predator adaptation called leg autotomy, similar to tail autotomy in lizards, salamanders, and some snakes. This means that their legs can break off when grabbed and will later regrow - better to lose a limb and escape than to be eaten whole. But Fordonia has evolved behaviors that exploit the crabs' ability to autotomize their legs - it pins the crab's body to the mud and pulls off its legs, eating them one at a time! Sometimes they also consume the crab's body, but often they just leave it behind. This makes Fordonia the only snake that breaks its prey apart prior to eating it, although we must admit that it is somewhat helped along by the crab's autotomy. This discovery was sufficiently exciting to be published in the prestigious journal Nature.
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| The five crab legs at the top, eaten by this snake, came from a crab about the size of the one on the bottom. The white circle represents the maximum-sized prey item the snake could have eaten whole. Figure from Jayne et al. 2002 |
The adaptations of Fordonia to cancrivory don't end there. As anyone who has eaten crab legs knows, a crab's exoskeleton is very tough - we humans must use tools to break into it. In order not to be internally lacerated by their prey, Fordonia have evolved extra tough, muscular stomach lining. Other crustacean-eating snakes, such as the North American crayfish snakes (genus Regina), as well as the arthropod-eating False Hook-nosed Snake (Pseudoficimia frontalis, a sonorine snake from western Mexican dry forests), also have thickened muscles surrounding their stomachs, to prevent internal damage from they prey's sharp exoskeletons.
Fordonia,Gerarda,Homalopsidae
