For the past century, vipers were thought to be the fastest thing in nature, and they represented the pinnacle of snake strike performance. Well, not so anymore, according to a new study published in Biology Letters this week. Harmless snakes can strike just as fast as venomous ones.
For many snakes, striking can serve two important purposes: catch prey and defend against predators. But strike performance has actually only been measured in very few species. Despite high-speed photography in 1954 that showed much slower strike velocities in rattlesnakes than generally expected, vipers are still thought to have the fastest strike among all snakes.
To debunk the viper’s strike, a University of Louisiana at Lafayette trio led by David Penning compared the defensive strike performance of 14 Texas ratsnakes (Pantherophis obsoletus) with that of vipers: six western cottonmouths (Agkistrodon piscivorus) and 12 western diamond-backed rattlesnakes (Crotalus atrox). Each snake was presented with a stuffed glove as a target, and the team measured defensive accelerations, velocities, and durations for the three species.
The strike performance of the ratsnakes matches, and sometimes exceeds, that of the vipers. All three snakes had similar strike accelerations, velocities, and durations. To the right, you can see the defensive strike of a ratsnake (top) and a rattlesnake (bottom) recorded at 250 frames per second.
The highest strike accelerations were 274 meters per second squared (m/s2) by a ratsnake and 279 m/s2 by a rattlesnake – far greater than the jumping accelerations of black-tailed jackrabbits and kangaroo rats.
One consequence of such impressive strike performances involves physiological tolerance: Rapid head-first accelerations like that in snake strikes may reduce blood flow to the brain. Humans rarely experience these accelerations. Fighter jet pilots launching from an aircraft carrier experience take-off accelerations of 27 to 49 m/s2. Without anti-gravity suits, they can lose consciousness at accelerations that are less than a quarter of the values achieved by snakes in this study. Even with anti-G suits, pilots lose the ability to stand up from sitting at accelerations of 30 m/s2, and they can't move their limbs when accelerations reach 78 m/s2.
The long distances between a snake's heart and head might impair cranial blood flow during strikes, but strike durations are very short. All three snake species can strike faster than the blink of an eye, which takes 202 milliseconds in humans.
Mammalian startle responses can activate muscles in 14 to 151 milliseconds, and they produce observable movement in as little as 60 to 395 milliseconds. But that’s still too slow. Harmless and venomous snakes can reach their targets in about 50 to 90 milliseconds.
Image in the text: D.A. Penning et al., Biol Lett 2016