Tuesday, June 26, 2012

Readers Write In: Do Snakes Eat Their Prey Alive? It Depends.

This e-mail (and picture) arrived in my inbox a couple weeks ago:

I recently happened to accidentally disturb a Ratsnake that was constricting a baby rabbit. When I touched the snake's tail, he uncoiled but began to start swallowing the rabbit. Because I interrupted the constriction, the baby rabbit was still alive but the snake continued to engulf it anyway. Is it unusual for a snake to consume a meal that is still alive?

Randy Y.
Midlands, South Carolina

  First off, I was glad to see that A) the snake in the picture was correctly identified as a normal component of the local wildlife and B) it wasn't bludgeoned to death.

  To answer this question, we must first consider why snakes constrict and kill their prey at all. To put it simply, snakes kill their prey because eating your dinner alive is a dangerous job when you have no arms or legs but prefer meals with sharp teeth, claws, and/or beaks.

  Squirrels, for example, are common meals for snakes. Squirrels are not generally known for their fearsome nature; but, you should have seen the little ones I helped cared for when I volunteered at a wildlife rehabilitation center many years ago. When I walked by their cages they would rush towards me repeatedly and bare their teeth in vicious displays of ferocity. In my memory, they roared. I'm not sure if I'm remembering that part correctly but I do know I was terrified when it was my turn to feed them.

   In any case, capturing a squirrel, rat, or even a rabbit, can be a dangerous proposition for a snake. So, what some snakes do is: 1) use their mouth to quickly grab their intended prey and, 2) in a flash, wrap their body around their soon-to-be meal and suffocate it. When the snake senses that their dinner's heart is no longer beating, the snake then begins to swallow it. I should add here that different kinds of snakes have different strategies for catching prey. In this post, I am speaking of the snakes, such as Ratsnakes, that are known as constrictors.

   That all makes sense, but as Randy observed, sometimes snakes skip the constricting step (you may remember me writing about how hognose snakes exhibit some similar behaviors). Why do snakes sometimes do skip constricting their prey? Well, when a snake is busy and pre-occupied with wrapping itself around a rat or other animal, the snake runs a high risk of becoming a meal for another predator, like a vigilant hawk. Another reason snakes might not want to constrict their prey before eating it is because it takes a lot of work and energy.

   Despite the risks of constricting their prey, a snake is not likely to skip this step when their meal could hurt them. A few laboratory studies have been conducted on the subject and it is generally thought that the more harmless the meal is, the more likely a snake will just start swallowing it without bothering to constrict it first. What kinds of meals don't represent a considerable danger? Baby rodents, birds, and rabbits, like the one in South Carolina. 

  Does it sound gross and distasteful to imagine swallowing defenseless prey? Well, what did you have for lunch?

Want to Learn More? Check Out These Scientific Articles:

A. Mori (1991). Effects of prey size and type on prey-handling behavior in Elaphe quadrivirgata Journal of Herpetology, 25 (2) DOI: 10.2307/1564643

A. de Queiroz (1984). Effects of prey type on the prey-handling behavior of the bullsnake, Pituophis melanoleucus Journal of Herpetology, 18 (3), 333-336 DOI: 10.2307/1564088

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