Gila monster

Gila monster
Conservation status
Near Threatened (IUCN 3.1)
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Reptilia Order: Squamata Family: Helodermatidae Genus: Heloderma Species: H. suspectum
Binomial name
Heloderma suspectum Cope, 1869

The Gila monster (pronounced /ˈhiːlə/, HEE-la), Heloderma suspectum, is a species of venomous lizard native to the southwestern United States and northern Mexico (but not Baja California). A heavy, slow moving lizard, up to 60 centimetres (2.0 ft) long, the Gila monster is the only venomous lizard native to the United States, and one of only two known species of venomous lizard in North America, the other being its close relative the beaded lizard (H. horridum).^[1] Though the Gila monster is venomous, its sluggish nature means that it represents little threat to humans. However, it has earned a fearsome reputation, and is often killed by hikers and homeowners, despite the fact that it is protected by state law in Arizona and Nevada.^[2][3]

Taxonomy and etymology

There are two subspecies of Gila monster: the reticulate Gila monster (H. suspectum suspectum) and the banded Gila monster (H. suspectum cinctum).^[2] The reticulate Gila monster lives in the southern region of the Gila monster's range, while the banded Gila monster is a northern subspecies occurring primarily in the Mojave Desert. The reticulate Gila monster tends to have its lighter markings broken up by dark scales, giving it a reticulated pattern, while the banded Gila monster generally have more unbroken bands of lighter scales.^[4][5]

The Gila monster has one close living relative, the beaded lizard (H. horridum), as well as many extinct relatives in the Helodermatidae whose evolutionary history may be traced back to the Cretaceous period. The genus Heloderma has existed since the Miocene, when H. texana lived, and fragments of osteoderms from the Gila monster have been found in late Pleistocene (8000-10,000 years ago) deposits near Las Vegas, Nevada. Because the Helodermatids have remained relatively unchanged morphologically, they are occasionally regarded as living fossils.^[6] Although the Gila monster appears closely related to the monitor lizards (varanids) of Africa, Asia and Australia, the wide geographical separation and unique features not found in the varanids indicates that the Gila monster is better placed in a separate family.^[5]

The name Gila refers to the Gila River Basin in Arizona, where they were once plentiful.^[7] Heloderma means "studded skin", from the Ancient Greek words Helos — the head of a nail or stud — and derma, or skin. Suspectum comes from the describer, paleontologist Edward Drinker Cope, who suspected that the lizard might be venomous due to the grooves in the teeth.^[6]

Description

Closeup of a Helodermatid's skin, composed of beadlike scales.

H. suspectum is a bulky, sausage-shaped lizard with a length of 30 centimetres (0.98 ft) to 60 centimetres (2.0 ft) and a weight of 1.3 kilograms (2.9 lb) to 2.25 kilograms (5.0 lb).^[8] Although smaller than the beaded lizard, which can grow to be a 1 metre (3.3 ft) long,^[9] the Gila monster is the largest lizard in the United States.^[8] It has a thick tail that is used to store fat, which it can live off of for months, or for years according to several anecdotes. Its tail is proportionately longer than that of the beaded lizard, a trait used to differentiate between the two. Unlike many other lizards, a Gila monster's tail does not autotomize and cannot grow back if broken. The Gila monster also possesses large forefeet and sharp claws, ideal for digging, as well as a thick black tongue, used to smell with the help of a Jacobson's organ.^[9]

The Gila monster's scales have the appearance of black, pink, orange, or yellow beads, laid down in intricate patterns. These beads are small bony plates that form scales, and are known as osteoderms.^[10] The colors of its osteoderms are more vivid than those of its close relative, the beaded lizard. The scales on the belly are rectangular rather than rounded. It was the beaded skin of the Gila monster that caught the attention of Native Americans, the designs of which are recreated in Native American art and basketry.^[11] The scales are most vivid when the Gila monster is young; as it ages, the colors become paler and more reticulated.^[9] The Gila monster sheds its skin in small patches, such that they always seem to be in the process of shedding. Complete molting is thought to occur once per year.^[12]

Distribution and habitat

A Gila monster's head. The bead-like scales can be observed, as well as the strong forelegs and claws suitable for digging.

The Gila monster is found in the Southwestern United States and Mexico, a range entailing Sonora, Sinaloa, Arizona, parts of California, Nevada, Utah, and New Mexico (but not Baja California). They inhabit scrubland, succulent desert, and oak woodland, seeking shelter in burrows, thickets, and under rocks in locations with ready access to moisture.^[4] In fact, Gila monsters seem to like water, and can be observed immersing themselves in puddles of water after a summer rain.^[13] They avoid living in open areas such as flats and farmland.^[14]

Ecology

maintains

Conservation status

Urban sprawl, the pet trade, and habitat destruction has affected Gila monster numbers. As a result, Gila monsters are protected by Arizona and Nevada state law; it is illegal to "harass, harm, pursue, hunt, shoot, wound, kill, trap, capture, or collect the Gila Monster." In 1952, they became the first venomous animal to be given legal protection.^[13][15][16] Gila monsters are listed as Near Threatened by the IUCN.^[3] The San Diego Zoo was the first zoo to successfully breed Gila monsters in captivity, doing so in 1963.^[17]

Relation with humans

Though the Gila monster is venomous, its laggard movement means that it poses little threat to humans. However, it has earned a fearsome reputation, and is often killed. Among Native American tribes, the Gila monster had a mixed standing. The Apache believed that its breath could kill a man, and the Tohono O'Odham and the Pima believed that it possessed a spiritual power that could cause sickness. In contrast, the Seri and the Yaquai believed that the Gila monster's hide had healing properties.^[14] The Gila monster has even starred as a monster in a B movie, The Giant Gila Monster. Myths that the animal's breath is toxic enough to kill humans, that it can spit venom, or leap several feet in the air to attack are all false.^[17] Another myth held that the Gila monster did not have an anus and therefore expelled waste from its mouth, the source of its venom and "fetid breath".^[9]

References

Further reading

• Beck, Daniel D. (2005). Biology of Gila Monsters and Beaded Lizards. Berkeley: University of California Press. ISBN 0-520-24357-9. 
• Capula, Massimo; Behler (1989). Simon & Schuster's Guide to Reptiles and Amphibians of the World. New York: Simon & Schuster. ISBN 0671690981. 
• Carmony, Neil B.; Brown, David (1991). Gila Monster: Facts and Folklore of America's Aztec Lizard. Silver City, NM: High-Lonesome Books. ISBN 0-944383-18-1. 
• Cogger, Harold; Zweifel, Richard (1992). Reptiles & Amphibians. Sydney, Australia: Weldon Owen. ISBN 0831727861. 
• Ditmars, Raymond L (1933). Reptiles of the World: The Crocodilians, Lizards, Snakes, Turtles and Tortoises of the Eastern and Western Hemispheres. New York: Macmillian. pp. 321. 
• Freiberg, Dr. Marcos; Walls, Jerry (1984). The World of Venomous Animals. New Jersey: TFH Publications. ISBN 0876665679. 
• Roever, J. M.; Hiser, Iona Seibert (1972). The Gila Monster. Austin, Tex: Steck-Vaughn Co. ISBN 0-8114-7739-8.