Kinematics of strikes in venomous snakes.

Venomous snakes owe their evolutionary success in part to the effectiveness of their strike. The success of a strike depends on reaching the prey quickly before it startles and has the chance to escape. Here, we present the first ever large-scale experiment comparing strike performance across 36 venomous snake species from three families (31 Viperidae, 4 Elapidae and 1 Colubridae). We used two high-speed video cameras (1000 frames s-1) to capture strikes at a ballistics gel prey and tracked the strike trajectory in three dimensions. The 3D coordinates were used to measure strike kinematics and performance. Kinematic performance was compared within Viperidae across predation style, diel activity pattern, diet, habitat type, temperature and first jaw contact with prey. Kinematic variables (peak velocity, peak acceleration, gape angle, start distance, contact angle, head size) varied by the part of the jaw that first contacts the prey. Start distance to prey also varied by peak acceleration, jaw gape angle and contact angle with prey. Vipers typically reached higher peak velocities than elapids; however, some elapids such as Acanthophis rugosus reached equally high velocities. Peak velocities were found to be higher in ambush predators and in snakes that prey on mammalian prey. Prey was often reached within 100 ms, which falls within the mammalian startle response. Behavioural differences across the three families were also observed: Viperidae performed a smooth strike that was often followed by fang repositioning; Elapidae reached their prey quickly, bit and repeatedly squeezed prey with their jaws; and Colubridae used their rear-positioned fangs by alternate jaw movement to damage the prey's surface.