The Iguanids Sauromalus obesus Family: Iguanidae Genus: Sauromalus Species: obesus Range: Southwestern United States and northwestern Mexico The chuckwalla is the largest nonvenomous lizard in the United States, reaching lengths of 8 inches snout to vent. The tail length usually matches that of the body. The body is dorso-ventrally flattened, and is very plump. The coloration is gray-brown, often mottled and slightly banded. Like all other members of the family Iguanidae, the chuckwalla is primarily herbivorous, dining on tender shoots and bushes in their native habitat. In captivity, a good diet consisting of vegetables and fruits can be offered, such as collard greens, mustard greens, escarole, dandelion greens, green beans, winter squashes, bell peppers. (For more detailed information about herbivore diet, jump to the information I have written on giant green iguanas.) Chuckwallas are diurnal and have evolved to bask in the hot desert sun, which has two repercussions regarding housing. First, chuckwallas need to be exposed to temperatures between 90 and 100 degrees Fahrenheit during the day. This is best achieved through use of incandescent spotlights. A basking spot can be created by directing the hottest light toward a flat rock, and a temperature gradient can be created by using less powerful lights in other areas of the cage. During the day, the coolest part of the enclosure should be in the low 80s, and nighttime temperatures can drop to the low 70s. Second, chuckwallas need exposure to light in the UV-B range. Access to natural, unfiltered sunlight is the best way to provide the lizards with UV-B exposure. Full spectrum fluorescent bulbs can be used to supplement UV-B exposure, but natural sunlight is preferred and far superior. Exposure to UV-B facilitates the production of vitamin D3 in the chuckwalla, which is essential for calcium absorption. In their native environment, chuckwallas are ground-dwellers, wedging themselves between rocky crevices to avoid predation. The environment to be created for them in captivity should have ample floor space, and need not be very tall. It should be dry, and rocks can be furnished in order to provide hiding places. A substrate such as outdoor carpet or paper (unprinted newspaper, brown bags) can be used, which is easily changed when soiled. Males are very territorial and should not be housed together. Females are egg-layers.