MEHTA, Rita; MOON, Brad*; UC Davis; University of Louisiana: The Scaling of Constriction Strength Snakes

Constriction was probably one of the key innovations that enabled snakes to subdue relatively large prey animals. It involves a snake placing its body around a prey animal and squeezing, which restrains the prey from escaping and defending itself, and typically kills it quickly. Published observations and experiments on constriction have indicated that it is strong enough to kill prey by suffocation, circulatory arrest, or spinal fracture. However, constriction strength has been measured in very few species of snakes, and thus far only in relatively small individuals. In this study, we derived quantitative predictions about the constriction pressures exerted on prey by snakes of different sizes, and we tested these predictions by measuring constriction pressure in 11 species of snakes. We predicted that constriction pressures range from 38-250 kPa in snakes 1-30 cm in diameter, and we measured pressures of 5-175 kPa in snakes 0.85-12.5 cm in diameter. Constriction pressure varied significantly with snake diameter (in the region that forms the coil) and number of loops in the coil. The measured pressures are high enough to kill many kinds of prey animals by circulatory arrest or spinal fracture, both of which are faster than killing prey by suffocation alone, and therefore are safer for the constrictor. These results help explain how constriction has been a key mechanism in the feeding biology and evolution of snakes.