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Facts About the Gila Monster

Tanmay Tikekar
Gila monsters are poisonous lizards found in North America. This story describes these fascinating animals...

Killer Medicine

Components of Gila monster venom are being studied as a possible cure for diabetes!
The Gila monster, Heloderma suspectum, is found in the Mojave Desert in the US and Mexico. It is one of the largest lizards in the world, excluding monitor lizards. It gets its name from the Gila River basin in Arizona. Gila monsters used to be quite populous in that region, but their numbers have dwindled in recent decades.
Their toxicity contributed to their binomial name; the scientist who discovered the animal, Edward Drinker Cope, suspected that the lizards might be venomous, and thus gave them the name.


Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Superfamily: Varanoidea
Family: Helodermatidae
Genus: Heloderma
Species: H. suspectum

Physical Description

Gila monsters are among the longest and largest lizards. They can reach lengths of up to 2 feet, and can weigh up to 5 lb.
They measure up to 6 inches at birth. They are conspicuous due to their orange and yellow-speckled black skin, and their slow, lethargic behavior. Being cold-blooded, they rely on the external temperature to regulate their internal body temperature.
They are often found in underground burrows, shrubs, and under rocks, but are rarely found far from a water source. Gila monsters maintain a body temperature of about 30 °C. Despite this high temperature, they are not quick sprinters, but have a relatively high endurance among lizards.

Diet and Predators

Gila monsters primarily feed on eggs and carrion.
They also feed on birds, small rodents, frogs, and insects, but eggs make up the vast majority of their diet. They can eat up to one-third of their body weight every time they eat, but their meals are very infrequent. In the wild, these venomous lizards only feed up to ten times a year!
Gila monsters have an extremely strong sense of smell, and extensively rely on it to find food. They don't inject venom with snake-like 'fangs', but instead bite the victim and keep chewing, spreading their venom through serrated, grooved teeth.
Gila monster venom is a mild neurotoxin, and is harmful to humans, but Gila monsters are so lethargic that a 19th century doctor wrote, rather forcefully, "...I have never been called to attend a case of Gila monster bite, and I don't want to be. I think a man who is fool enough to get bitten by a Gila monster ought to die..."!

Life Cycle

Gila monsters become sexually active after 3-4 years. Their mating season starts around May, and carries on into early July. The female lays around 5 eggs (although as many as 12 have been observed), and buries them 5-6 inches under the sand.
The hatchlings are born after 9 months, around April of the next year. After reproducing, adult Gila monsters start their hibernation, in order to escape the hot summer. Gila monsters live for up to 20 years, though they may exceed this in captivity.

Relationship With Humans

Like so many animals, the Gila monster is being affected by habitat loss, but not to an irreparable degree. It is listed as 'Near Threatened' by the IUCN Red List. It was the first venomous animal to be legally protected, and it is illegal to kill them in Arizona and Nevada.
Due to it being a fairly large, venomous reptile, various native myths portrayed it as a fetid, deadly creature. Needless to say, all these myths are untrue. Gila monsters are essential animals in their desert habitat, and are not at all dangerous to humans.