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
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
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
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.
University of Cincinnati. July 2002.