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Everyone knows that snakes swallow their meals in one giant gulp, so University of Cincinnati biologist Bruce Jayne and his colleagues were astonished to discover a tropical snake that eats at a much different pace. The snake, found in Singapore, feasts on soft-shelled crabs which it tears apart and swallows one bite at a time.
The discovery by Jayne, Harold Voris of the Field Museum of Natural History, and Peter Ng of the National University of Singapore, is reported in the July 11 issue of Nature.
"The snake literally rips the crab's body apart," said Jayne. "They'll tug and pull on it to tear it apart."
The researchers were trying to understand the diets of two snakes found in Singapore – Fordonia leucobalia and Gerarda prevostiana. Both eat crabs, which is fairly unusual right from the start. However, while examining the stomach contents, it was obvious that crabs eaten by Gerarda were in pieces. Since crabs can drop (autotomize) their limbs and joints can break as a crab is captured and eaten, it was important to verify how the crab is actually pulled apart.
So, Jayne brought the snake into his laboratory and recorded Gerarda's feeding behavior using an infrared IR) camera. "They're kind of a bashful species," said Jayne. They wouldn't eat when I watched them, but when I used the IR camera I found out there was this stereotypical behavior."
The snake forms itself into a loop and uses the loop to hold and tear apart its prey. The ability to rip the crabs apart was a surprise, because snake teeth are not adapted for slicing and cutting. Instead, they curve back into the mouth which is an adaptation for holding the prey inside the mouth.
Fordonia, on the other hand, has no stereotypical behavior for pulling its crab prey apart, although they do occasionally break the legs off hard-shelled crabs. "When fed soft-shell crabs, they make a mess of it," said Jayne. That limits the size of prey Fordonia can eat while Gerarda can capture and ingest much larger prey.
"The term is gape, the size of the mouth opening," explained Jayne. "Most snakes are limited to prey they can swallow whole. It's a little mind-boggling, but prey size limits must be rethought. We don't know what the upper limit is now."
There is another benefit to preying on soft-shell crabs, according to Jayne. Gerarda prefers freshly molted crabs which have very little mobility. "That means they can feed with impunity. There's almost no cost." Other benefits include being able to consume prey more quickly.
In contrast, Fordonia eats primarily hard shell crabs and can be injured while capturing and swallowing its prey. "Eating any hard-bodied animal is a task. It's a very tough chore for a snake."
Jayne said the take-home message is that you shouldn't jump to conclusions about vertebrate behavior by relying solely on anatomical evidence. The research was funded by the National Science Foundation.
Journal
Nature