Frogs and snakes are not known to be friends. Folktales from many parts of the world document this fact repeatedly. In fact frogs and snakes are on such unfriendly terms that snakes often eat frogs, and very occasionally frogs eat snakes as well.
I witnessed this very event, that being a snake eating a frog, behind a road side rest area bathroom on Rt. 9 in Beddington Maine. Yes nature can happen anywhere, even somewhere as unglamorous as behind the rest stop, in the gravel. The snake was a common garter snake, Thamnophis sirtalis. These snakes are the most abundant reptiles in Maine and are found in a wide variety of habitats, including water, they swim quite well. As ectotherms you will find them sunning themselves to regulate their body temperature, as they cannot internally generate enough heat to support a high enough metabolism to be active. In the winter they hibernate in groups. This time of year the females are giving birth to live young. Some sources state that up to 80% of the common garter snake’s diet is earth worms, but they eat a wide variety of prey depending on availability, prey that can include frogs, leeches, slugs, rodents, small birds, fish, insects and molluscs. Generally they eat size appropriate prey, the bigger the snake, the larger the prey they can consume. At one point in my life I came up with a rule for eating, one I think is pretty reasonable, and I have followed it, for the most part, ever since. That rule is: don’t eat anything bigger than your head, and it works for me. Snakes don’t follow that rule, to a pretty astonishing degree. And snakes can’t take bites, they don’t have the proper dentation, nor appendages with which to gain leverage. They have to swallow whatever the catch whole (and usually alive). In order to do this they have to make their heads a great deal bigger, which is accomplished by unlatching their jaws, and having very stretchy skin, which allows their mouths to expand around their prey. Even while their skin expands to accommodate the prey, the muscles of their throat strongly pulse and move the prey towards the stomach, completing the swallow. I don’t often think of snakes as having strong muscles, but when I saw the snake pick the frog up off the ground and slither away with it, I gained a new appreciation for just how robust these creatures are.
The frog in question was a pickerel frog, Rana palustris. They are wide spread in Maine, and after reproducing in wet areas in the spring, they disperse into fields, meadows and damp woods for the summer.
The scene I came upon was this: the snake was biting the frog’s ankle, having not swallowed any part of the frog yet. The frog, for its part, was just laying there, seemingly paralyzed. It looked to me like one good kick and it would be free, but I probably underestimate the power of the snake’s bite strength. The snake kept chomping away on the ankle, apparently trying to maneuver the frog’s foot deeper into its mouth, so its throat muscles could start helping pull the frog in, in this initial phase it was all about the snake’s mouth, and whatever progress it could make with its incurved teeth and biting action. As we watched, and at this point, quite a crowd had gathered, the snake reared up and dragged the frog a few feet away, the frog all the while passively submitting. An occasional twitch or light kick, and its breathing were all we had to tell us it was alive. By the time we left, the snake had managed to swallow one of the frog’s legs up to the hip, and even though I know that snakes can eat prey much larger than one would expect, I still had my doubts.
Watching this I had what I suspect was a typical reaction; I wondered if I should try to intervene and “save” the frog, especially right at the beginning when the snake just had it by the ankle. I thought about how terrible it must be to be eaten alive, to be fully conscious (as conscious as a frog gets) while being slowly swallowed, your head and face the last to be part of you to be drawn in. I realized though that it while it is easy to sympathize with the frog, the snake, even though it is the predator in this case, is no less vulnerable. It was going to take some time for the snake to actually swallow that frog, time when the snake was completely defenseless and would be easy prey. All manner of larger vertebrates, from hawks and owls, to foxes and raccoons, would be happy to munch on a garter snake who’s biting teeth were otherwise occupied. I began to feel real empathy for this snake, who, by simply eating, as we all must eat, was exposing itself to danger with no real means of defending itself, a true vulnerability. We often say that life isn’t fair, but maybe that isn’t true. Maybe life is completely fair, and when we see the balance of nature so dramatically illustrated, the frog losing its life, the snake endangering its life to eat the frog, we have to admit that. We’re the ones that don’t play fair, but we should remember, in the long run, nature wins, every time.
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References:
If you Google “ Frog and Snake” folk tales you will get lots of stuff. This is a nice one from Timor:
http://www.ling.hawaii.edu/ldtc/languages/tetum/Little%20Frog%20and%20Little%20Snake.html
The standard reference for us Mainers, and useful throughout the northeast: Maine Amphibians and Reptiles, Mac Hunter, Aram Calhoun and Mark McCollough, University of Maine Press
From Northern State University in Aberdeen South Dakota: http://www3.northern.edu/natsource/REPTILES/Garter1.htm
Terrific series of photos of a garter snake eating a large green frog: http://www.flickr.com/photos/steve_byland/467564987/
