Gila Monster

Characteristics

This is one of only two venomous lizard species in the world, (the other is the Mexican beaded lizard, Heloderma horridum). Gila monsters are large and stout, gaudily patterned lizards, with brightly colored bead-like scales on their backs. The skin coloration is black with contrasting pink, yellow and orange. The heavy-bodied lizard has a short, fat tail that stores fat it can live off of during periods of food shortage. The limbs of the lizard are stout and have heavy claws.

Species Specifics

Sexual Dimorphism is quite subtle, but adult males have somewhat wider heads.

Physical Characteristics

Ecology

Habitat

They live in semi-desert of scrub with rocky outcrops, in places where moisture is readily accessible. They are found under rocks, in burrows of other animals, and sometimes in holes it digs itself.

Distribution

The Gila monster ranges from extreme southwestern Utah, southern Nevada and adjacent to San Bernadino County, California; southeastward through west and south Arizona and southwestern New Mexico. It can be found south into Mexico through Sonora to northwestern Sinaloa. It ranges from sea level to 1500 meters in altitude.

Diet

Carnivorous. Small mammals, lizards, frogs, insects, carrion, birds and birds' eggs. They sometimes eat quail eggs whole, without crushing the shell.

Ecological Web

Secondary consumer.

Activity and Behavior

Activity Pattern

Nocturnal. They spend 95% of their time underground and emerge only to hunt for food or to take a sunbath. They don't need to eat very often, because they can store fat in their large tails.

Behavior

Once they bite, they will not usually let go on their own and must be pulled off. The longer this takes, the more venom they will excrete into the bite! Unlike most lizards, they come out at night!

Social Behavior

Although primarily solitary, Gila monsters seem to have a loose social structure and occasionally share shelters.

Reproductive Behavior

Males compete for mates by engaging in carefully choreographed wrestling matches, in which the biggest and strongest lizard wins. These lizards mate during the summer. Mating begins with a male tongue-flicking to seek a female's scent, while rubbing his cloaca on the ground. When a male finds a female, he lies by her and rubs his chin on her back and neck while holding her hindlegs. If a female objects to the male, she will try to bite him while crawling out from underneath. If receptive, she raises her tail. The male then moves his tail under hers, bringing their vents into contact. Copulation lasts from 30 minutes to an hour. The female then digs a hole, lays a clutch of 3-5 large, leathery, oval-shaped eggs in the hole, (about 5" below the surface) and covers them. The eggs are not buried very deep, so the heat of the sun incubates them. About 10 months later, the baby Gila monsters break out of their eggs and crawl to the surface.

Offspring

Offspring are only a few inches long, but look like vibrantly-colored miniature adults. The hatchlings are then ready to begin life on their own, no training required!

Conservation

Status

Listed as Near Threatened by IUCN. Gila monster populations are shrinking due primarily to human encroachments, and they are considered a threatened species! They were the first venomous animal in North America to get legal protection. It is illegal to collect, kill or sell them in Arizona!

Historical

Current Threats

Our Role