The mechanics and muscular control of constriction in gopher snakes (Pituophis melanoleucus) and a king snake (Lampropeltis getula)

Constriction of prey by gopher snakes Pituophis melanoleucus and king snake s Lampropeltis getula is highly variable in posture, muscular activity and force exertion. These snakes typically use lateral bends of the anterior tr unk to wind the body into a vertical coil around the prey. Three common con striction postures are fully encircling loops that form a coil, partially e ncircling loops, and non-encircling loops that pinion the prey. Initial tig htening of a coil occurs by winding or pressing the loops tighter to reduce the diameter of the coil. The epaxial muscles are highly active during str iking and coil formation and intermittently active during sustained constri ction. These results refute the hypothesis of a mechanical constraint on co nstriction in snakes with elongate epaxial muscles. Constricting gopher and king snakes can detect muscular, ventilatory and circulatory movements in rodent prey. In response to simulated heartbeats or ventilation in mice, th e snakes twitch visibly, recruit epaxial muscle activity, and increase cons triction pressure temporarily, but then quickly relax. Muscular activity an d constriction pressure are increased most and sustained longest in respons e to muscular struggling in prey. Although muscle activity and pressure exe rtion are intermittent, the constriction posture is maintained until the pr ey has been completely still for several seconds; thus, a snake can reapply pressure in response to any circulatory, ventilatory or muscular movement by the prey. The pressures of 6.1-30.9 kPa (46-232 mm Hg) exerted on small mammal prey by constricting snakes range from about half to over twice a mo use's systolic blood pressure, and are probably 10 times larger than the ve nous pressure. These high pressures probably kill mammalian prey by inducin g immediate circulatory and cardiac arrest, rather than by suffocation alon e.