Every so often I like to cover a species that, while not recommended as a pet, is well worth a closer look. One such lizard that I have had the good fortune of working with is endemic to North America, the strikingly-marked Gila Monster.
Note: Gila Monsters are bred in captivity and sometimes appear for sale in the pet trade. Please do not let your interest in these admittedly fascinating creatures lead you to purchase one. They are venomous, and, despite recurring rumors to the contrary, have caused human fatalities. Gilas are considered by many to be somewhat docile and slow moving. Having long cared for them as a zoo herpetologist, I can assure you that this is not so. They are often inactive, but can bite with amazing speed – and, in contrast to many snakes, there is no preparatory coil or other movement to warn of their intentions. If anything, their generally calm demeanor can lull one into a sense of false security – indeed, Gila bites are among those most frequently suffered (and covered up!) by zoo keepers. Observe them in public collections and the wild, but please leave captive care to zoos.
This stoutly built creature is the USA’s heaviest native lizard, outweighed only by Florida’s introduced Green Iguanas and Nile Monitors.
The scales, underlain by boney plates known as osteoderms, are bead-like in appearance. The body is marked in widely varying patterns of pink, black yellow and orange blotches. The blunt tail serves as a food-storage vessel – during lean times it may lose 20% or more of its mass. Adult size ranges from 9 to 24 inches.
Two subspecies, the Reticulate Gila Monster and the Banded, are recognized. They are found in western, central and southern Arizona and adjacent New Mexico, southwestern Utah through Nevada and from southwestern California to Sinaloa in northern Mexico.
Although typically thought of as a desert-dwelling species, Gila Monsters do not live in overly dry, central desert areas. Rather, they frequent arid desert fringes and habitats that are referred to as “succulent or vegetated deserts” – areas that usually support a heavy growth of succulent plants, cacti, grasses and shrubs. They may also be found in semi-arid plains and rocky foothills, lightly wooded thickets and about farms, usually near streams, springs or other sources of moisture. Gilas sometimes enter oak forests and in Sinaloa, Mexico, inhabit the lower slopes of mountains and nearby beaches.
Gilas may forage above-ground but are otherwise largely fossorial. They occupy burrows dug by gophers and other mammals or those of their own making, abandoned woodrat nests and cavities below large rocks.
Despite the arid climate prevalent in their range, Gila Monsters favor areas of high humidity and spend the vast majority of their time in fairly moist underground retreats. When kept in dry zoo exhibits, Gilas will soak in water bowls for hours on end.
Gila Monsters are diurnal in the springtime but become largely nocturnal as summer progresses. During the hottest parts of the year they generally appear above ground only after rains.
Status in the Wild
Gila Monster populations are declining due to habitat loss and, in some cases, collection for the pet trade. They are protected by law in all states within their range, are listed on CITES Appendix II and classified as Near Threatened by the IUCN.
Gilas feed on slow-moving animals – most commonly young mammals still in the nest, i.e. ground squirrels, kangaroo rats, pocket gophers, rabbits and cactus mice. They also take the eggs and chicks of doves, quail and other ground-nesting birds, lizards and their eggs, tortoise eggs, locusts and other large insects and carrion.
These lizards are well-adapted to a harsh environment in which food is often scarce. They gorge when food is available, consuming up to 50% of their bodyweight, and in some areas eat but 3-4 large meals annually.
Mating occurs in April and June, with 3-12 eggs being laid from July through August. The eggs are buried in the sand, usually in a location exposed to full sun. The eggs do not hatch until the following May – 10 months after being laid. This long incubation period is a function of seasonality within the Gila’s range…artificially incubated eggs have hatched in as few as 30 days.
Captive longevity exceeds 28 years; unknown in the wild.
The Beaded Lizard, H. horridum, 4 subspecies of which dwell in Mexico and Guatemala, is a close relative of the Gila and the only other member of the family Helodermatidae. These 2 species were, until recently, considered to be the only venomous lizards (please see below). In contrast to venomous snakes, the venom glands of Gila Monsters and Beaded Lizards are in the lower jaw and the teeth are grooved rather than hollow. Venom flows into the mouth through ducts that open between the teeth and gums. In order to insure the venom’s introduction into a prey animal or enemy, both lizards retain a firm grasp when biting.
In 2005, researchers at Australia’s Melbourne University discovered that the Bearded Dragon, Pagona vitticeps, produces a mild venom (other Agamids are being studied). Several monitor lizards, including the Komodo Dragon, Varanus komodoensis and the Lace Monitors V. varius, were also found to produce venoms of varying strengths. Studies of Lace Monitor venom have revealed that it causes the lizard’s prey to rapidly loss consciousness by affecting the blood’s pressure and clotting ability. This venom is likely the source of the strong reaction, previously attributed to oral bacteria, that is often associated with bites inflicted by monitor lizards upon people.
A synthetic version of a chemical found in the saliva of the Gila Monster is the basis of an important medication used to treat Diabetes Type II.
The species name, suspectum, was coined in 1869 by renowned herpetologist and paleontologist Edward Drinker Cope – upon noting the Gila’s grooved teeth, he “suspected” that it was venomous! The genus name, Gila, is taken from the Gila River Basin in Arizona.
Thanks, please write in with any Gila Monster related observations or questions. Until next time, Frank.
You can read more about the Gila Monster and the reptiles and amphibians that share its habitat at the web site of the Arizona Sonora Desert Museum:
Image referenced from Wikipedia Commons at http://en.wikipedia.org/wiki/Image:Gila_monster2.JPG and posted by Blueag9