You might not think of lizards as venomous reptiles, but the fact is many species of lizards do produce venom. Scientists believe up to 100 of the approximately 5,000 known lizard species have some form of venom. The majority of these venomous lizards pose no threat to humans, though.
Poison vs. Venom
Though "poison" and "venom" are often used interchangeably, and though both rely on the transmission of toxins from one organism to another, poison and venom are different concepts. Poisonous animals, like poison dart frogs, have a toxin that is present on or in their bodies. This toxin can cause irritation, sickness or death if it is ingested or absorbed by another animal. Venom, on the other hand, is intentionally injected into an animal through a special bodily adaptation -- a pit viper’s fangs or a bee’s stinger, for example. Animals that inject a toxin are considered to be venomous.
Gila Monster and Mexican Beaded Lizard
For many years scientists believed only two species of truly venomous lizard existed: the Gila monster and the Mexican beaded lizard. Both of these species are members of the Helodermatidae family and both are native to the Sonoran desert of North America. These lizards produce venom in glands within their lower jaws. They bite to inject, and they will often chew on prey to make the venom penetrate deeper. Though bites from Gila monsters and beaded lizards can cause painful bites, nausea and respiratory issues, human deaths from envenomation are rare.
Monitor lizards, such as the Komodo dragon, have long been known to deliver nasty bites capable of taking down prey much larger than themselves. Until recently scientists thought the monitor lizards transferred infectious bacteria from their mouths to the prey. According to National Geographic, however, scientists have confirmed venom produced by the lizard itself is responsible for the hunting success.
As with side effects of bites from monitor lizards, side effects of bites from some iguana species, such as swelling and excessive bleeding, have been traditionally blamed on bacteria in the lizards’ saliva. However, several species of iguanas, including many that are kept as pets, have been found to have primitive venom glands in their jaws, both upper and lower, that are able to produce and release a small amount of venom into what they bite.
Though lizard venom was once thought to have evolved separately from the venom system of advanced snake species, a 2005 study from the University of Melbourne suggests that snake and lizard venom systems may actually share a common origin. Considerable overlap in toxins exists between venomous snake species and venomous lizard species. While the system of delivery differs -- snakes inject venom through sophisticated fangs while lizards have more primitive glands that mix venom with saliva -- the common toxins suggest a shared lineage.
- New Scientist: Lizards' Poisonous Secret Is Revealed
- National Geographic: Komodo Dragons Kill With Venom, Researchers Find
- Reptile Channel: Venom or Poison
- Molecular and Cellular Proteomics: Functional and Structural Diversification of the Anguimorpha Lizard Venom System
- The International Wildlife Museum: Lizards - The Dangerous and the Deadly
- Nature: Early Evolution of the Venom System in Lizards and Snakes