Yes they do bite and it was recently discovered that both monitor lizards and iguanas produce venom. A bite from a monitor lizard causes swelling and can result in excessive bleeding. There are about 30 species of monitor lizard varying in size from 2/3 foot to 10 feet. They usually try to escape when confronted. But if that is not an option they will first strike with the tail and then bite. Most injuries occur from their large claws.