The evolution of chemical signals and predator-prey interactions among snakes

Chemicals from predators responded to defensively by prey are a type of chemical releasing stimuli referred to as a kairomone. A number of vertebrates detect chemicals from some of their predators. One case of the chemical detection of predators occurs among New World snakes, where crotaline snakes respond to skin chemicals of some ophiophagous colubrid snakes such as kingsnakes (Lampropeltis getulus) and indigo snakes (Drymarchon corais).

A zoo survey of the responses of crotaline snakes to ophiophagous snakes revealed a defensive body bridging response by more than 20 crotaline taxa for which the response has not previously been reported. Some ophiophagous snakes that have not previously been reported to elicit a body bridging response in crotalines were discovered.

Observations of the responses of garter snakes, Thamnophis spp., and other colubrid genera indicate that they discriminate between chemicals from some generally ophiophagous colubrid snakes and nonophiophagous colubrid snakes with different methods of odor presentation. Thamnophis spp. tongue flicked more to chemicals from ophiophagous snakes than to chemicals from nonophiophagous snakes when (1) presented with snake-derived chemicals on cotton swabs, (2) introduced into tanks conditioned by stimulus snakes, or (3) presented with snake odors in an olfactometer. Observations of encounters between Thamnophis and snakes were inconclusive.

Several litters of kingsnakes (Lampropeltis getulus) were tested for responses to snake-derived chemicals. Lampropeltis tongue flicked more to cotton swabs treated with snake skin chemicals from the copper head (Agkistrodon contortrix) than to many other stimulus conditions. Some kingsnakes in one litter attacked swabs treated with snake skin chemicals and attempted to ingest them. An olfactometer experiment indicates that kingsnakes perceive airborne chemicals from other snakes.

The published diets of ophiophagous snakes are examined, and comparisons are made between the snake species present in nature and those in the stomachs of ophiophagous snakes. Some snake species appear more often in the stomachs of ophiophagous snakes than others, and it may be that they are more vulnerable to ophiophagous snakes in nature.