A medium sized (up to 1,026 mm or 40" in total length) light gray-brown to gray snake with a prominent dark brown lyre-shaped marking on the top of the head and a dark bar crossing the top of the head between the eyes. There are fewer than 30 (an average of 24) dark, orange-brown, jagged-edged blotches on the back.
Each dorsal blotch is outlined in pale gray and divided by a pale-gray central crossbar. Small dark additional markings are present on the sides of the body between the primary blotches. The head is broad posteriorly and is clearly distinct from the slender neck. The eyes are large and the pupils are vertically elliptical. The underside is light cream, yellow, or gray, occasionally with sporadic dark brown flecking. The scales are smooth.
This snake is found across nearly all of southern Arizona and is likely found in most ranges in the western part of the state. Populations (possibly isolated) have been documented in the lower Grand Canyon, The Black Mountains of Mohave County, and the Kofa mountains of Yuma County. In Arizona this snake occurs at elevations ranging from just a few hundred feet above sea level to over 5,000'.
It is found in a variety of biotic communities in Arizona including Sonoran, Mohave, and Chihuahuan desertscrubs, Semidesert Grassland, Interior Chaparral, Great Basin Conifer Woodland, Madrean Evergreen Woodland, and the lower reaches of Petran Montane Conifer Forest. It is usually encountered in rocky habitat above the flats. It frequents boulder-strewn hillsides, steep slopes, and rocky canyons.
This snake is nocturnal but it can be found basking in sun-warmed rock crevices on warm days in spring and fall. It hibernates during the cold months of late fall and winter. It is chiefly a ground-dweller but is capable of climbing. Although this snake usually does not bite when captured it is capable of injecting mild venom with enlarged, grooved teeth in the rear portion of its upper jaw. Bites to humans reportedly cause mild swelling and irritation.
The Western Lyresnake uses its venom to subdue lizards, small mammals, bats, and birds. It also has the ability to constrict its prey.
A clutch of up to 20 eggs is laid in late summer.
The Sonoran Lyresnake apparently hybridizes with the Chihuahuan Lyresnake (Trimorphodon vilkinsonii) in extreme southeastern Arizona and southwestern New Mexico.