‘Playing dead’ observed in Xenochrophis piscator as a defense strategy

Checkered Keelback (Xenochrophis piscator) is a small but strong bodied snake. An excellent swimmer with a rounded head with a broad tapering snout is effectively streamlined. Its robust, stout and muscular body is capable of rapid movement. The coloration varies considerably but it is often olive brown or olive green dorsally and pale brown or white underneath. Often the dorsal coloration is accompanied by lighter spots arranged in a checkered pattern.

Behavior: A very active snake usually active by day but it may hunt frogs by night. It has a very vicious temper and will strike repeatedly without hesitation the instant it senses that it cannot escape its challenger. Often it will keep hold until its jaws have to be forced apart in order to disengage. It is semi aquatic in habit and seldom ventures beyond the vicinity of water. If chased over long distances it may even jump clear off the ground in order to escape often repeatedly.

Food: This snake as its name suggests is piscivorous, consuming frogs and tadpoles as well. This snake usually stalks its prey and grasps it with its vice-like jaws and if in a favorable position begins to swallow it immediately. Often frogs will croak for a considerable amount of time from within this snake's stomach before succumbing to its venom due to inefficient venom delivery mechanism.

On May 1, 2007, a call came in for a displaced snake from Sola crossing in Ahmedabad city. The snake was hiding in a pile of stones. It was a Checkered Keelback. While we were returning, we were called back for more snakes. One by one, 13 hatchlings were caught. Clutch of hatched out eggs was also discovered. Everything was collected from the same pile.  75 eggs counted. 5 of them were ‘failed’ eggs, showing a high success rate. I assume that the female (it was later sexed in the rescue center) was the ‘mother’ and was guarding the eggs. The hatchlings were a day old as the eggs had not yet dried out fully. As the hatchlings started coming out, the mother must have also come out.

In the evening, the babies and the mother were taken out for a photo session. The mother, as expected, snapped, but only once. Then suddenly, she started behaving oddly. She started dying!!! I could not make out if she was actually dying or mimicking. Then she let out a very foul smelling ‘substance’ from her anal gland. Now I could link up the defense strategy.

(And she did it every time, when handled!!!) 

Baby brown snakes (Storeria dekayi) are the latest addition to the long list of animals that practice some form of the strategy scientists call extreme immobility also known as 'Letisimulation'. Gerald, a physiological ecologist at Miami University in Oxford, Ohio, described his findings in August at the annual meeting of the Animal Behavior Society.

In the U.S. Hognosed snakes, genus Heterodon are well known for letisimulation. For many years, it was thought that letisimulation, was an inherent behavioral trait. Since these snakes feed almost exclusively on toads, it was later discovered that the accumulated toxins ("Bufonitoxins") located in their Parotoid Glands had somehow interacted w/ the snake's physiology, so when the snake is disturbed or otherwise bothered, these built-up toxins would cause the behavior of "Playing Dead" 

The list of animals that play dead includes 21 snake species but I have never heard or read about a Xenochrophis piscator playing dead… 

"So  question arises: Could a snake sp. "evolve" a behavioral trait, outside of a physiological response (or, conversely, "inside" a behavioral response)?" - rightly commented by Harry A. Shankman, a herper in U.S.