21 May 2008

Rat snake on the towpath

Let my shoe provide a scale.

This long black rat snake (Elaphe obsoleta) was stretched motionless across the C&O Canal’s towpath last Saturday. Its frozen stance, a characteristic defense mechanism used by rat snakes, was probably in response to the potential threat I posed to it. It remained motionless, while I approached within about a meter or maybe less. Nor did it seem to mind the blinding flashes of light coming from my camera. A similar behavior was also displayed by this individual.


One bicyclist showed up during the photo session. I let her know that a snake was blocking the path. Luckily, she wasn’t too terrified, passed behind the snake and continued on her way. The snake still didn’t move. Only after I walked away, did it start to crawl slowly and into the grass it went.

Many predators are probably more likely to spot a moving prey than a motionless one. Therefore, remaining motionless helps an animal escape detection. In this case, however, the strategy seems to backfire: the animal is exposed in the middle of a bare area where its dark body creates an easily noticeable contrast against the light background. Then again, the snake may now be mistaken for a tree branch. Such bare areas may indeed be present in the snake’s habitat, for example along river banks that are flooded frequently. So maybe this is not an example of an evolutionary trap.


Cindy said...

Wow, it looks weird. So...kinky! When I first saw it, I thought for sure you were going to say it had been run over.


Butch Norden of the Maryland DNR, who originally identified these snakes for me, commented in an e-mail:
"That kinked appearance is seen from time to time in this species, and has been commented on in the literature. Glad you found it and not someone with a big stick!"

nanotheater said...

Saw one of these in my backyard- when I walked back there it froze in a 'kinked' position a little more extreme than the photo. I stepped back a little and a fight with a rabbit resumed, with the rabbit attacking the snake and getting in a few good bites- before the snake climbed a tree- later we saw it looking for a meal in a nearby tree. thanks for the photo- it made identification easier.

Robert Denham said...

Just saw this rat snake posture on a paved road in my neighborhood. My dog was ahead of me and stopped sniff the snake. It remained frozen in a very kinked/corkscrew position. I was worried that a car would run over it, but after I continued my walk, and looked back, it had disappeared.
SW Virginia