It’s snake-eat-snake: a California kingsnake consuming a western rat snake David Penning, Missouri Southern State University

How can a predator catch and consume prey bigger than itself? That’s one of the marvels and mysteries of the appropriately named kingsnake.

Kingsnakes can kill and consume rat snakes at least 20 per cent larger than themselves. Now we may finally know how they manage to ensnare their quarry in the first place.

Imagine trying to fit a large garden hose inside a small one. The kingsnake faces a similar challenge in engulfing a bigger tube-shaped animal. We know that they achieve this with flexible jaws and by crushing prey inside S-bends, like squeezing spaghetti through a pasta machine.


But a lingering mystery was how these smaller snakes have the power to subdue and handle those bigger than themselves – an extra-challenging feat because unlike mammals that suffocate and become unconscious quickly, snakes survive anoxia for much longer and can thus put up a fight.

Perplexed by this puzzle, David Penning at Missouri Southern State University, Joplin, and Brad Moon at the University of Louisiana at Lafayette used three experiments to investigate.

First, they examined 36 preserved specimens of three kingsnake and three rat snake species to examine how much muscle they had relative to their body size. They also measured how much force snakes could exert while trying to pull away, to assess escape performance for 98 snakes restrained with a harness.

An eastern kingsnake consuming a Texas rat snake David Penning, Missouri Southern State University

Surprisingly, they found that kingsnakes did not have a greater proportion of muscle for their size in comparison with rat snakes, nor did they exert a proportionally greater pulling force. All bigger individuals had more muscle and pulling force, regardless of species.

In a third experiment, the researchers shook dead mice in front of 182 snakes to stimulate them to engage in a struggle with their prey. Sensors attached to the mice allowed measurement of how much constricting pressure kingsnakes exerted compared with ratsnakes.

King-sized pressure

What prey-squeezing observations revealed was very different levels of constriction pressure – with all kingsnakes producing higher pressures than the rat snakes.

The most powerful kingsnake species studied, the California kingsnake (Lampropeltis californiae), exerted more than double the constricting pressure of the weakest of the three rat snake species, the western rat snake (Pantherophis obsoletus).

What seemed to be key to creating their power was the way they positioned the coils in their bodies. “Almost all the rat snakes had this really variable, haphazard application of their body, whereas all the kingsnakes were in this elegant, spring-like pattern,” says Penning. The king, it seems, is well-sprung.

An eastern kingsnake constricting with a uniform coil David Penning, Missouri Southern State University

Its posture appears to make the kingsnake’s constriction method more efficient and powerful, although that hypothesis still needs testing further.

“It’s fascinating to see such a similarity in muscle size and strength translate into such a major difference in constriction force,” says Rick Shine at the University of Sydney in Australia. “Clearly, evolution has fine-tuned superficially similar systems to produce very different performance outcomes. It’s a fascinating glimpse into the world of snake-eat-snake.”

Journal reference: Journal of Experimental Biology, DOI: 10.1242/jeb.147082

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