A few weeks ago, one of our two male Red-sided Garter Snakes (Thamnophis sirtalis parietalis) — the last of the great litter of 2002 — decided to bite himself, at which point he recoiled in alarm and surprise. He and his brother are curious and friendly (albeit very ravenous: they’ll bite your fingers, though it’s not personal; they’re just hungry), but they’re just not very smart.

By no means is that the first time I’ve seen one of my snakes bite itself. Normally it’s something I associate with Common Kingsnakes (Lampropeltis getula); I recall seeing both California and Speckled Kingsnakes chew on themselves. Apparently it’s more than a kingsnake thing.

Last week, though, I was summoned to answer a question on Ask MetaFilter from someone whose son’s California Kingsnake chewed on its own tail on more than one occasion. You can read my answer there; I’m going to flesh it out a bit more (and organize it a bit better) here.

To understand why some snakes might bite themselves, you have to keep the following three points in mind:

1. Snakes aren’t very smart (and kingsnakes aren’t very smart even by snake standards).
2. Some snakes freak the fuck out when eating.
3. Snakes are never hungrier than just after they’ve eaten.

Let me explain each of those points.

Snakes aren’t very smart (and kingsnakes aren’t very smart even by snake standards). I’ve often joked that a snake’s brain functions can be expressed in about 30 lines of Perl. My pet theory — which itself isn’t much more than a joke, either — is that kingsnakes are even stupider than the average snake. Kingsnakes are known as snake eaters (which is why you can’t have more than one in a cage as a rule), but will pretty much eat anything. They don’t, in other words, discriminate in terms of what they eat; the part of the brain that asks whether something should be eaten has been replaced with a simple NOM! I suspect that if it moves and is small enough, they will try to eat it.

(They’re also immune to rattlesnake venom; I also suspect that it was easier for kingsnakes to evolve immunity to venom than it was for them to grow additional brain power.)

Some snakes freak the fuck out when eating. I’ve observed that captive kingsnakes tend to go a little crazier than other snakes at feeding time — they tend to lose what little mind they have when attacking their food. Corn and pine snakes, for example, tend to be pretty placid feeders, so much so that I’ve been able to feed them on my lap; I wouldn’t dare do this with a kingsnake. They. Just. Freak. Out.

Now, remember how one of my garter snakes bit himself earlier this month? I’ve also noticed some garter snakes freaking the crap out during feeding time — especially that one, his brother, and his father, all of whom would bite willy-nilly at everything that moved (and some things that didn’t) — except, of course, the mouse that was dropped in front of them.

(Among garter snakes it seems to be a male thing: males are pretty hyper to start with; females are much calmer and matter-of-fact about eating, though they have much bigger appetites.)

Snakes are never hungrier than just after they’ve eaten. At least that’s what I’ve observed in our collection: snakes that have just eaten a pretty big meal seem awfully eager to have another one. They’re often looking for more, and there’s an explanation for that. In the wild, snakes tend not to eat at regular intervals: they raid an entire mouse or bird nest, or gobble down many frogs just after they’re transformed. Food is not available regularly, so they tend to gorge when it’s available — after all, there might not be another chance like that for a month or two.

Feeding mode, in other words, is like a switch that is left on for a while. It’s most often during this time, then, that a wound-up snake might get confused and bite itself.

A related scenario I’ve observed is when snakes bite their cagemates immediately after feeding — but only then. I’m talking about snakes that have shared a cage for the better part of a decade, and are fed separately: sometimes one of them is still a little wound up when put back into the cage, and tags his or her cagemate. Usually only once, and usually the snake settles down pretty fast, but in the meantime we’re watching that snake very carefully, and making a note to give that snake more time by itself in its feeding cage before putting it back in with its roommate. I’ve seen this happen with gopher snakes and rat snakes, neither of which has a reputation for cannibalism. It’s just something that can happen when one of them gets wound up.

So my best guess is that certain snakes lose their shit when feeding, and in the confusion bite themselves (or their cagemate), thinking it’s more food. Eventually they settle down, so it’s not like people have to worry about their pet snakes turning themselves into Ouroboros at any moment.

Just keep an eye on them after they’ve eaten.