FACTORS ASSOCIATED WITH THE MASS OF VENOM EXPENDED BY PRAIRIE RATTLESNAKES (CROTALUS-V-VIRIDIS) FEEDING ON MICE

The purpose of this study was to assess through correlation analyses the various factors and consequences associated with the mass of venom injected by prairie rattlesnakes (Crotalus v. viridis) into their natural prey, deer mice (Peromyscus maniculatus). Fifty-seven predator prey interactions were studied via slow motion videotape review. The mass of venom expended by snakes during biting was quantified by enzyme-linked immunosorbent assay (ELISA) of whole-animal homogenates. The quantity of venom expended was not related to size of prey; however, the range of mouse sizes (13-31 g) was quite narrow. Multiple bites of the same mouse were not associated with incremental increases in venom expenditure; only about 40% more venom was expended by striking prey a second time. The duration of fang contact and site of fang penetration had no discernible effects on venom expenditure. The site of fang penetration of prey appeared to be random, due to evasive actions of the mice. The components of striking (duration of launch, fang contact, and recoil, respectively) and distance of the strike were correlated and appeared to be influenced by the prey's reaction. After striking and releasing mice, the snakes did not attempt to relocate more quickly those prey which succumbed to venom relatively quickly. Both natural (snakebite) and artificial (syringe) injections indicated that the site of venom injection (e.g. anterior, posterior, muscle, vital organ) has a greater influence on subsequent mobility and survival of mice than the quantity of venom injected. It appears that some behavioral aspects of predation (especially the sequential components of striking) are flexible and responsive to prey reactions, while others (venom expenditure and poststrike immobility) are less subject to modification.