Lizard heads called the parietal eye, a basal ("primitive") feature also present in the tuatara. This "eye" has only a rudimentary retina and lens and cannot form images, but is sensitive to changes in light and dark and can detect movement. This helps them detect predators stalking it from above. Until 2006 it was thought that among lizards, only the Gila monster and the Mexican beaded lizard were venomous. However, several species of monitor lizards, including the Komodo dragon, produce powerful venom in their oral glands. Lace monitor venom, for instance, causes swift loss of consciousness and extensive bleeding through its
Mexican beaded lizard October. Males engage in ritual combat that often lasts several hours; the victor mates with the female. The female lays her clutch of two to 30 eggs between October and December, the clutch hatching the following June or July. Young lizards are seldom seen. They are believed to spend much of their early lives underground, emerging at two to three years of age after gaining considerable size. The beaded lizard is surrounded by myth and superstition in much of its native range. It is incorrectly believed, for example, to be more venomous than a rattlesnake, can cause lightning strikes with