The scaling of terrestrial striking performance in western ratsnakes (Pantherophis obsoletus).

In many organisms, juveniles have performance capabilities that partly offset their disadvantageous sizes. Using high-speed video recordings and imaging software, we measured the scaling of head morphology, axial morphology, and defensive strike performance of Pantherophis obsoletus across their ontogeny to understand how size and morphology affect performance. Head measurements were negatively allometric whereas the cross-sectional area (CSA) of epaxial muscles displayed positive allometry. The greater relative muscle CSA of larger ratsnakes allows them to produce higher forces relative to their mass, and those forces act on a relatively smaller head mass when it is thrust forward during striking. Maximum strike accelerations of 70-273.8 ms-2 and velocities of 1.08-3.39 ms-1 scaled positively with body mass but differed from the geometric predictions. Velocity scaled with mass0.15 and acceleration scaled with mass0.17 . Larger snakes struck from greater distances (range = 4.1-26 cm), but all snakes covered the strike distances with similarly short durations (84 ± 3 ms). The negatively allometric head size, isometry of anterior mass, and positively allometric muscle CSA enable larger P. obsoletus to strike with higher velocities and accelerations than smaller individuals. Our results contrast with the scaling of strike performance in an arboreal viper, whose strike distance and velocity were independent of body mass. When strike distance is modulated, all other performance capacities are affected because of the interdependence of acceleration, velocity, duration, and distance.

Debunking the viper's strike: harmless snakes kill a common assumption.

To survive, organisms must avoid predation and acquire nutrients and energy. Sensory systems must correctly differentiate between potential predators and prey, and elicit behaviours that adjust distances accordingly. For snakes, strikes can serve both purposes. Vipers are thought to have the fastest strikes among snakes. However, strike performance has been measured in very few species, especially non-vipers. We measured defensive strike performance in harmless Texas ratsnakes and two species of vipers, western cottonmouths and western diamond-backed rattlesnakes, using high-speed video recordings. We show that ratsnake strike performance matches or exceeds that of vipers. In contrast with the literature over the past century, vipers do not represent the pinnacle of strike performance in snakes. Both harmless and venomous snakes can strike with very high accelerations that have two key consequences: the accelerations exceed values that can cause loss of consciousness in other animals, such as the accelerations experienced by jet pilots during extreme manoeuvres, and they make the strikes faster than the sensory and motor responses of mammalian prey and predators. Both harmless and venomous snakes can strike faster than the blink of an eye and often reach a target before it can move.