Heloderma suspectum

A large, heavy-bodied lizard with a massive head, short thick tail (thin in emaciated individuals), beadlike dorsal scales, short limbs with strong claws, and loose folds of skin on the neck; dorsal coloration gaudy, black and pink, orange, or yellow; adult snout-vent length 22-35 cm (Stebbins 1985). Occasionally exceeds 50 cm in total length (Campbell and Lamar 1989, which see for further description details).

Differs from other U.S. lizards in large size and bulk, beadlike dorsal scales, and bold dorsal pattern of black and yellow, orange, or pink. Differs from the similar H. HORRIDUM of Mexico as follows: tail length less than 55% of snout-vent length (vs. at least 65%); 48-62 scales in longitudinal midline from vent to tip of tail (vs. 74-87); dorsal coloration includes yellowish, orange, or pink (vs. black with or without yellow). See Campbell and Lamar (1989) for further details.

Occupied vegetation types include desert grassland, Mohave and Sonoran desert scrub, and thorn scrub (Sonora); less often oak or pine-oak woodland. In Mexico, it occurs on lower mountain slopes and adjacent plains and beaches (Stebbins 2003), sometimes in irrigated areas. Canyon bottoms, arroyos, and rocky slopes may support relatively dense populations in some parts of Arizona and Sonora. In southern Arizona, the Gila monster is more abundant in wetter and rockier palo verde-sahuaro desert than in drier and sandier creosote-bursage desert, where it occurs mainly in or near rocky buttes or mountains (Lowe et al. 1986). In New Mexico, the species is most commonly associated with desert scrub vegetation in rocky regions of mountain foothills and canyons; sometimes it is found along the lower fringes of pinyon-juniper woodland or oak woodland; rarely encountered in agricultural areas (Degenhardt et al. 1996). Gila monsters are mainly terrestrial but infrequently climb into vegetation. Refuges include spaces under rock, dense shrubs, burrows, or woodrat nests. Sub-surface shelters are important components of the habitat, and certain ones are used with a high degree of fidelity (particularly in winter), sometimes by multiple individuals concurrently (Beck and Jennings 2003). In Arizona, Gila monsters spend about 98% of the year under cover (Lowe et al. 1986). In Utah, individuals spent over 95% of active season underground; occasionally they basked near shelters in spring; shelters were burrows or crevices in rocky areas; hibernacula faced south (Beck 1990).

Basically solitary but may use communal overwintering sites.

In southern Arizona, sperm formation occurs in May-June; females have oviductal eggs from late June into August (Goldberg and Lowe 1997). Eggs are laid primarily in July-August. Clutch size averages about 6, ranges up to 13 (Goldberg and Lowe 1997). In Arizona, eggs reportedly overwinter underground and hatch the following late April-early June, after an incubation period of about 10 months (Lowe et al. 1986, Goldberg and Lowe 1997). Females are sexually mature at about 24 cm SVL; mature females evidently reproduce every year (Goldberg and Lowe 1997).