The gila monster’s skin is covered with beadlike scales which are known as osteoderms. Their scales are coloured black with a pattern of yellow or pink stripes and spots running along the length of their body. They have a large tail which is used to store fat much like the hump of a camel. When they eat it expands in size. At the end of their short legs are long claws which are used to dig.
At 56cm (22in) long the gila monster is the largest lizard in the US. They weigh about 1.8kg (4lbs).
In the wild they will only eat about five to ten times a year. On these occasions they may eat 1/3 of their body mass. Prey is eaten alive if it is small or they may crush larger prey items to death.
They have a very good sense of smell with one locating an egg buried 15cm (6in) below the ground.
Gila monsters come from Mexico and the southwestern United States. In the US they can be found throughout Sonora Arizona, California, Nevada, Utah and New Mexico.
Primarily they are found in desert areas. They prefer areas which are rocky as opposed to open flats and agricultural areas. They can also be found in oak woodlands. They enjoy being near water and are often found immersing themselves in it.
Mating takes place between May and June. Males will fight to obtain mating rights for a female. The winner will initiate courtship with the female by flicking his tongue. She may reject his advance and inform him of this by biting him.
After a successful mating two-twelve eggs are laid 13cm (5in) below the sand in July or August. Incubation takes nine months with the eggs hatching between April and June.
Following the hatching gila monsters are ready to go. They measure about 16cm (6.3in) long and are already equipped with venom.
Sexual maturity is achieved at three to five years old.
Predators of the gila monster include birds of prey, coyotes and humans. A number of other animals will also eat their eggs. They warn predators they are dangerous by opening their mouth wide and hissing.
Gila monsters make their home in burrows. They may dig these themselves or use ones which have been dug by desert tortoises. Over the cold winter months they do not leave their burrows and live solely off the fat reserves in their tails.
While mostly solitary on occasion gila monsters have been spotted sharing burrows.
They are one of only two species of venomous lizard in the world. Instead of injecting the venom like a snake they chew the prey item which forces the modified saliva into the bite. The bite of a gila monster is as toxic as that of a coral snake. Gila monster bites are not typically fatal to humans due to the small amounts which are injected per bite.
One of the characters in the 2011 film Rango was a gila monster.
San Diego Zoo was the first to breed gila monsters in captivity during 1963.
Gila monsters were named after Arizona’s Gila River.
A drug which helps to manage Type 2 diabetes has been produced using a protein from gila monster saliva.
Their scientific name “Heloderma suspectum” means studded skin.
Hammerson, G.A., Frost, D.R. & Gadsden, H. 2007. Heloderma suspectum. The IUCN Red List of Threatened Species 2007: e.T9865A13022716. https://dx.doi.org/10.2305/IUCN.UK.2007.RLTS.T9865A13022716.en. Downloaded on 26 April 2020.
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