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The Short-Horned Lizard is classed as a non-desert species. As compared to other species of Phrynosoma, it is quite cold-tolerant, which accounts for its occurrence at high elevations and high latitudes. SHLs are the most widely distributed species of Horned Lizards in the United States. The main value of Canadian populations of this species lies in their scientific interest. The ecology of high latitude lizards is very poorly understood. In addition, hernandesi are noteworthy of being deemed the world's most northerly representative of the much studied family Iguanidae.
P. hernandesi are 2 1/2" to 4" SVL, up to 6" overall. Females grow to larger sizes than males, who tend to stop growing after their first year. SHLs are flat-bodied, squat lizards with short spines crowning the head. They have a snub-nosed profile and short legs. The trunk is fringed by one row of pointed scales, while the belly scales are smooth. Their main colors are gray, yellowish, or reddish-brown, and there are two rows of large dark spots on the back. When hernandesi are threatened or become aggressive, their colors are much more vivid and intense.
The Short-Horned Lizard is the most widely distributed species of Phrynosoma in North America. They occur in the widest range of habitats as well; near pebbles and sandy soil, areas of shortgrass prairies, sagebrush deserts, woodlands, and semi arid plains at higher elevations, sometimes altitudes up to 11,000ft (3350 m).
Short-Horned Lizards are live-bearing or viviparous (probably an adaptation to cold climates) and have been known to produce broods as large as 31. Mating in April and May, the lizards have a gestation period that is approximately three months long. SHLs give birth in August and September to young that usually have a body length of about 25 mm when born. Sexual maturity is attained, in males, in the summer after the first winter dormancy. For females it has not been determined. As well, recapture records suggest that females live as long as five years, but as of yet no such estimate has been made for the male SHL lifespan.
Diurnal. High cold tolerance. SHLs are most active during the afternoon, burrowing at night. They rely on camouflage to avoid predators. When threatened, they will puff up their bodies and hiss, while pointing their horns forward. They can squirt blood from their eyes, as well as handle much cooler temperatures than most other Horned Lizards. This species tends to hibernate by late Fall to mid-Spring.
In the wild, Short-Horned Lizards feed mainly on ants, but will take grasshoppers, termites, beetles, wasps, caterpillars, spiders, and moths. The females, due to a greater size, tend to feed on larger prey items as well as wider size range of prey.
The range of P. hernandesi is large, extending from Saskatchewan and Alberta Canada, through Montana, Utah, Colorado, Arizona, New Mexico and into Mexico through northeastern Sonora, Chihuahua, and Durango. The P. Douglasii species is located most abundantly around the Columbia River Basin and the Great Basin.
Phrynosoma hernandesi are currently listed as rare and vulnerable.
Short-Horned Lizards are listed as "rare" in the state of South Dakota; SHLs are protected from collection, capture, and disturbance without special permits. In the United States, they are also protected in Texas and Oregon. This species is listed as "vulnerable" by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC). The major threat to its survival is the development of its habitat for grazing cattle, or for mining oil and gas. Both activities change the landscape to a significant degree, and consequently push out these fragile lizards in the process.