Blainville's Horned Lizard
by Naturalist Michael Marchiano
The Coast or Blainville’s Horned Lizard (Phrynosoma blainvilli) is considered to be an odd-looking creature by many people. Squat, flat bodied, and short-tailed with a wide head covered in spines, it causes one to consider the little lizard a miniature relic from the age of dinosaurs. In fact, its appearance gives rise to its nickname, “Horny Toad”. Growing to a length of five inches, this cryptic colored lizard depends far more on its appearance for survival than speed or agility. Its mottled coloration of large and small patches and bands on its body of various shades of brown, black, cream, and yellow allow it to blend into it environment almost to a point of invisibility.
When threatened, it will first freeze and hope its camouflage will protect it. If attacked, it will run a short distance, stop suddenly, lay flat, and once again count on its coloration for protection. If grabbed, the horned lizard has a unique defense for repelling its attacker. It can actually squirt a quick stream of blood from the corner of its eyes with the hope of distracting or startling the predator and escaping.
Another unique feature of this specialized lizard is its diet. Its primary food is native ants, such as species of harvester and carpenter ants. It does on occasion eat other arthropods such as beetles, crickets, and spiders, but 80-90 percent of its diet is indigenous ants. The introduction of Argentine ants (which have replaced native species) in areas once inhabited by Coast horned lizards has been one cause of their diminished numbers. These introduced ant species are not palatable to the lizard.
Although three subspecies of this lizard inhabit California, from Baja up the Central Calley to the Sierra Buttes, the last vestige of these unique creatures in Contra Costa County is Mount Diablo. The overall population of the Coast horned lizard throughout California has been under threat because of habitat destruction, pesticides, agriculture, and the introduction of Argentine ants.
Blainville’s horned lizards are generally seen in our coast range and the Central Valley from spring through fall, hibernating in burrows under ground in cold weather. Found in chaparral, mixed oak, and grey pine forest, sandy loam soil, and gravelly areas, these lizards need a mixture of open space and shrubbery with soil they can easily dig into as well as populations of native ants for food.
They breed in spring, with the female laying a small clutch of eggs (average 8-12) in a burrow she excavates. Newborns hatch in late summer or early fall and are miniatures of their parents, about the size of a quarter.
Once much more common in Contra Costa County, the population has decreased in recent years. On Mount Diablo keep your eyes open, especially on Eagle Peak, Twin Peaks, Black Point, White Canyon, Mount Olympia, and on the south side along Black Hawk Ridge.
Because of its specialized diet and environmental conditions, this is a lizard that does not do well in captivity (horned lizards in North America can no longer be sold in the pet trade) so please enjoy them when you see them, but let them be. Enjoy this unique and marvelous creature along with the rest of the natural environment in Mount Diablo State Park.