Effects of Venom on Prey

The basic effects of venom that contribute to prey death can be quite varied but may include interruption of the parasympathetic nervous system (Gennaro et al., 2007) or hemorrhagic effects and inflammation (Zeni et al., 2007) (see Venom Composition and Production page for more general information on the effects of venom). Perhaps more interestingly, venoms are suspected to have effects that are not solely related to prey death (Chiszar et al., 1999; Kardong, 2002; McCue, 2007). For example, Chiszar et al. (1999) found that western diamondback rattlesnakes were able to distinguish between envenomated and non-envenomated prey based on chemosenory cues. One hypothesis is that the snakes are able to detect the effects of the lytic enzymes in the venom; such a chemosensory ability would certainly be useful in locating prey after a strike (Chiszar et al., 1999). McCue (2007) investigated the digestion of rattlesnakes to see if prey injected with venom are more easily digested as had been previously speculated.  There was little evidence to suggest that the specific dynamic action (SDA; essentially how much energy is used in digestion) was different between envenomated and non-envenomated prey treatments, but design issues with the experiment suggest that further investigation is needed.  Furthermore, even if venoms do play a role in chemical digestion, such an effect may not result in a large difference in SDA values since a majority of metabolic cost associated with SDA may be the result of protein synthesis which would not differ among treatments (McCue, 2007).

An eastern diamondback rattlesnake (Crotalus adamanteus) eating a cottontail rabbit. Photo by Drew Sanders.

Prey organisms as a speices may also be altered by natural selection because of the effects of snake venom (Heatwole and Poran, 1995; Heatwole et al., 1999).  As would be expected due to natural selection, Heatwole and Poran (1995) found that sympatric eels were more resistant to sea snake venoms than were allopatric eel species.  Heatwole et al. (1999) suggest that there may also be an ontogenetic effect on prey resistances.  In bullfrog tadpoles, which are unlikely to be preyed upon by snakes, resistances to the venoms of copperheads and cottonmouths were low, but as they metamorphosed into adults their resistance to venom increased (Heatwole et al., 1999).