Naive ophiophagus lizards recognize and avoid venomous snakes using chemical cues.

Monitor lizards prey on snakes. Conversely, venomous snakes prey on juvenile monitor lizards. Immediately after hatching, monitor lizards are naive to all prey items, thus correct assessment of snake prey is paramount for survival. Experiments were conducted to determine how hatchling monitor lizards (Varanus albigularis) with no previous exposure to snakes reacted to sympatric venomous and nonvenomous snakes. Hatchling lizards attacked harmless snakes, but avoided venomous species. Lizards readily accepted meat from skinned snakes, regardless of species. When invertebrate prey covered with skin segments from venomous snakes were restrained from moving, they were usually investigated by tongue-flicking and rejected. Unrestrained skin-covered prey, however, were generally attacked and eaten without prior evaluation by tongue-flicking. Attack was inhibited in trials in which unrestrained prey were tongue-flicked, suggesting that chemical cues contained in snake skins mediate avoidance of venomous snakes. Selection for the ability to perceive snake integumental chemicals may be especially strong in species that both consume and are consumed by snakes.