Knob-Scaled Lizards: Xenosauridae

These lizards are ambush hunters, which means that they sit very still and wait for their meal to come to them. Their meals are usually made up of insects that happen to come too close to their hiding places, which are usually in rock crevices. The lizards quickly grab the insects and gulp them down. Like other lizards, these species flick their tongues to pick up chemical odors from their insect prey. They cannot smell with their tongues, but they can smell with a special organ, called a Jacobson's organ, that sits above a small opening on the roof of the mouth. The lizard picks up the chemicals with its tongue and places them on the opening. A study of tongue-flicking behavior in Xenosaurus platyceps found that the young ones flicked their tongues to smell prey whether the lizards were in their hiding places or not, while the adult lizards did most of their tongue-flicking only when they were in holes or cracks. In other words, the adults were much more interested in finding prey when they were out of sight than when they were in the open.

At least one species of knob-scaled lizards, the Newman's knob-scaled lizard, will also eat bits of plants and some mammal meat. This suggests that the lizards may prefer insects but will eat just about anything they can find. Scientists call such animals opportunistic (ah-por-toon-ISS-tik), because they include almost any kind of plant or animal in their diet—if they are hungry and the opportunity presents itself.