iPhoneOgraphy – 22 Oct 2016 (Day 296/366)
The Gila monster (Heloderma Suspectum) is a species of venomous lizard native to the southwestern United States and northwestern Mexican state of Sonora. A heavy, slow-moving lizard, up to 60 cm (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 lizards in North America, the other being its close relative, the Mexican beaded lizard (H. horridum). Though the Gila monster is venomous, its sluggish nature means it represents little threat to humans. However, it has earned a fearsome reputation and is sometimes killed despite being protected by state law in Arizona.
In this species, the largest extant lizard native to North America north of the Mexican border (non-natives like green iguanas are larger), snout-to-vent length is from 26 to 36 cm (10 to 14 in). The tail is about 20% of the body size and the largest specimens may reach 51 to 56 cm (20 to 22 in) in total length. Body mass is typically in the range of 350 to 700 g (0.77 to 1.54 lb), with 11 males having been found to average 468 g (1.032 lb). Reportedly, the very heaviest, largest specimens can weigh as much as 2,300 g (5.1 lb).
The Gila monster has one close living relative, the beaded lizard (H. horridum), as well as many extinct relatives in the Helodermatidae, the evolutionary history of which 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 (10,000–8,000 years ago) deposits near Las Vegas, Nevada. Because the helodermatids have remained relatively unchanged morphologically, they are occasionally regarded as living fossils. Although the Gila monster appears closely related to the monitor lizards (varanids) of Africa, Asia and Australia, their wide geographical separation and the unique features not found in the varanids indicate the Gila monster is better placed in a separate family.
The name “Gila” refers to the Gila River Basin in the U.S. states of New Mexico and Arizona, where the Gila monster was once plentiful. Heloderma means “studded skin”, from the Ancient Greek words helos (ἧλος), “the head of a nail or stud”, and derma (δέρμα), “skin”. Suspectum comes from the describer, paleontologist Edward Drinker Cope, who suspected the lizard might be venomous due to the grooves in the teeth.
The Gila monster is found in the Southwestern United States and Mexico, a range including Sonora, Arizona, parts of California, Nevada, Utah, and New Mexico (potentially including 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. In fact, Gila monsters seem to like water and can be observed immersing themselves in puddles of water after a summer rain. They avoid living in open areas such as flats and farmland.
The Gila monster emerges from hibernation in January or February and mates in May and June. The male initiates courtship by flicking his tongue to search for the female’s scent. If the female rejects his advances, she will bite him and crawl away. When successful, copulation has been observed to last from 15 minutes to as long as two and a half hours. The female lays eggs in July or August, burying them in sand 5 in (13 cm) below the surface. The clutch consists of two to 12 eggs: five is the average. The incubation lasts nine months, as the hatchlings emerge during April through June the following year. The hatchlings are about 16 cm (6.3 in) long and can bite and inject venom upon hatching. The juveniles typically have larger bands of pink scales than adults, although the banded Gila monster (H. s. cinctum) has a tendency to retain the band pattern. H. suspectum sexually matures at three to five years old. After egg-laying, adult Gila monsters gradually spend less time on the surface to avoid the hottest part of the summer (although they may be active in the evening), eventually starting their hibernation around November.
Little is known about the social behavior of H. suspectum, but they have been observed engaging in male-male combat, in which the dominant male lies on top of the subordinate one and pins it with its front and hind limbs. Both lizards arch their bodies, pushing against each other and twisting around in an effort to gain the dominant position. A wrestling match ends when the pressure exerted forces them to separate, although bouts may be repeated one after the other. These bouts are typically observed just before the mating season. Those with greater strength and endurance are thought to win more often and enjoy greater reproductive success. Although the Gila monster has a low metabolism and one of the lowest lizard sprint speeds, it has one of the highest aerobic scope values (the increase in oxygen consumption from rest to maximum metabolic exertion) among lizards, allowing them to engage in intense aerobic activity for a sustained period of time. Males have been observed to have higher aerobic scopes than females, presumably because of sexual selection for a trait advantageous in prolonged combat. The Gila monster may live up to 20 years in the wild, or 30 in captivity.