How to Kill a Snake When You’re a Snake

When two snakes fight, it can be hard to work out who’s winning. “They’re both wound together, just two tubes wrestling,” says David Penning, from the University of Louisiana at Lafayette. But if one of the combatants is a kingsnake, then all you have to do is wait. The kingsnake will be the one left slithering.

These animals get their name because they specialize in killing other snakes. They’ll take rodents, lizards, and birds as well, but snakes account for a quarter of their diet. They do so by constriction—wrapping their coils around their opponent and squeezing so hard that they trigger cardiac arrest.¹

The kingsnake will launch itself at, say, a ratsnake, bite it, and throw some coils around. Then it inches its way toward the victim’s head, alternating between shifting its bite and adding more coils. The ratsnake tries to escape, but almost never does. Penning has now watched hundreds of these bouts, and “it never ever seemed like the kingsnake is in trouble,” he says. Unless it’s a juvenile that has inadvisedly picked on a target several times its size, it always wins. And, to Penning, that made no sense.

Typically, when scientists study constrictors, they look at big ones like pythons or boa constrictors, as they attack mice or rats. “Big snakes are strong predators; small mammals don’t do well when squeezed,” says Penning. “Rarely is someone surprised when the snake wins that scenario.” But kingsnakes will successfully constrict victims that are the same size or bigger, and that are also constrictors. How do you kill something that’s larger than you, using the very same method that it uses to kill? Why don’t kingsnakes ever get counter-constricted?  

To find out, Penning and his colleague Brad Moon taped pressure gauges to pre-killed rodents, and then offered them to kingsnakes and ratsnakes—182 individuals from six different species. And they found a clear pattern: The kingsnakes exert about twice as much pressure as the ratsnakes. They look similar from the outside, but they somehow squeeze much harder. Why?

Penning and Moon ruled out two possibilities. They dissected several museum specimens and showed that kingsnakes are no more muscular²
than ratsnakes. They measured how strongly the snakes can pull against a restraint, and found that neither group is better at escaping than the other.

They suspect that kingsnakes instead are stronger because they throw more efficient coils around their prey. “The peer reviewers preferred ‘spring-like’, but I call it the ‘curly-fry pattern,’” says Penning. “It’s an elegant, tight coil. Whereas the ratsnakes look like someone dropped spaghetti on something. They squeeze in a really haphazard way.” Perhaps that’s why they’re so bad at regicide.

“I like that this study is driven by a novel idea, rather than by technology,” says Kate Jackson, from Whitman College. “The techniques used are relatively simple and the experiment could have been done long ago—only nobody had thought to take this approach until now.”

Penning next wants to check if the kingsnake’s coils really are more efficient, or whether there are subtler differences in their muscles. They may be the same size as a ratsnake’s, but could they generate more force? And what accounts for their phenomenal stamina? A typical fight can be over in a few minutes, but if the kingsnake is inexperienced, the wrestling can go on for six to seven hours. “Olympic wrestling bouts takes a few minutes,” says Penning. “This is like someone trying to do extreme weightlifting for hours.”

That same stamina also allows kingsnakes to easily overpower rattlesnakes, cottonmouths, and copperheads, which get exhausted after a few minutes of activity. Kingsnakes are immune to these vipers’ venom, so the vipers don’t strike—that would leave their heads exposed. Instead, they lift up their mid-sections and try to body-slam their attackers. That rarely works. Even these vipers, which we consider to be among the deadliest of snakes, cannot dethrone the kings.