Archives of The Cold Blooded News

The Newsletter of the Colorado Herpetological Society

Volume 29, Number 2;   February, 2002

The Horned Lizards - Genus Phrynosoma

by Tom Eichhorst

There are 14 or so species in a single genus and they are found from Canada in the north to Guatemala in the south and in the United States from the coast of California to Arkansas. They typically inhabit arid or semi-arid land and different species are found from sea level to 11,000 feet. A typical description would be of a small lizard, flattened to the ground and much wider than high, colored in browns and grays, with numerous spines and small horns.

Known as tapayin to early American Indians, it was the German naturalist Arend Wiegmann who coined the name Phrynosoma for the genus in 1828. This name comes from the Greek words phry for toad and soma for body. This "toad-body" was then combined with the obvious horned feature of the lizard and we got the popular name "horned toad" and then the name used by most every kid in the Southwest, "horny toad." The more proper common name is "horned lizard," but years of tradition are not about to fold anytime soon to professional herpetology. Before being scientifically named, these small, innocuous lizards were immortalized in designs on pottery and rock carvings by prehistoric dwellers of the Southwest. Both Anasazi and Mimbres cultures showed their fascination with the horned lizard in the many ways they depicted the small lizard in their art. This fascination carried into modern times as the horned lizard is still a popular theme in modern American Indian art as well as a well-known character in folklore. The logo for the New Mexico Herpetological Society used on this newsletter is a stylized horned lizard designed by our own Jaci Fischer.

When the Spanish explorers and settlers came to the Southwest the "little gnome of the desert" was reported back to Spain as one of the wondrous new animals of the new world. Later explorers found the horned lizards equally fascinating and Lewis and Clark on their famous journey to survey the nation's newly acquired Louisiana Purchase sent a live horned lizard back to President Thomas Jefferson. In fact, it was Captain Meriwether Lewis who first coined the name "horned lizard" in his written report. Since that time, countless thousands have been captured over the years and kept as curiosities or pets only to die a slow death due to the inability of their captors to provide for the lizard's specialized requirements. Horned lizards are extremely specialized in both diet and the environmental requirements of temperature, humidity, and proper lighting. As pets they tend to slowly waste away. But they were common, easy to catch, and cute. So even though less than suitable for the pet trade, they were caught and sold in great numbers.

There were also other exploitive uses of this unique little lizard. Many were caught and shipped to other states and countries for ant control. Even Hawaii imported horned lizards for this purpose. Of course the environment was unsuitable and there are none there today, although there are occasional reports of horned lizards in some of the southeastern states. In the early 20th century a booming trade in stuffed horned toads flourished - especially in California. The traffic and abuse of horned lizards finally resulted in California passing a law protecting the animal in the 1930s. Other states followed and New Mexico officially placed the horned lizard in a protected status in 1941.

In spite of protection many populations of horned lizards are declining. Even though protected in many states, a great number of horned lizards are illegally collected and shipped out for the pet trade every year. But this single pressure on the population is probably not responsible for any but temporary and localized population drops. Although most are easily caught, horned lizards are difficult to find. The real pressures and stresses to Phrynosoma species are varied. Horned lizards are prey for many animals. Over 100 horned lizard carcasses have been counted stuck on the needle sharp tips of the leaves of a sotol bush (Dasylirion wheeleri) by a single loggerhead shrike (Lanius ludovicianus). This small gray bird is but one of many animals that prey upon horned lizards - even though the lizard may not actually be consumed because of its protective spines. But predator pressures have existed for millions of years and the species remained viable. It is undoubtedly modern man's impact with urban sprawl, irrigated farmlands, insecticides, asphalt highways, off road vehicles, etc. that have taken the greatest toll and may have tipped the scales against the lizard. And in the last decade the final pressures of a fire ant invasion and maybe a new and deadly virus have really tipped the scales. Little can yet be reported about the virus, but the fire ants are a well-known problem. Fire ants are renowned for their ferocity in killing or driving away competitors. This includes harvester ants of the genus Pogonomyrmex, the principal food of horned lizards. The horned lizard may eventually become relegated to few desert areas too bleak to develop into golf courses and too dry for the fire ants. Seven species are found in the United Slates (plus a couple of subspecies and forms) and four of these reside in New Mexico.

New Mexico Horned Lizards
Texas horned lizard (Phrynosoma cornutum), is probably the best known horned lizard in the United States. It is found from western Arkansas to southeastern Arizona and Durango, Mexico to northern Kansas at elevations from sea level to 6,000 feet. This is probably the largest of the North American horned lizards with a snout to vent length of over 5 inches for females and almost 4 inches for males. The tail would add another couple of inches for the often-repeated size of 7 inches total length (a 6 inch specimen is a monster, 7 inches is way out there on the bell curve - maybe too far). Texas horned lizards have 6 large cranial horns, with the middle 2 being the largest and the outer pairs joined at the base. They also have a double row of spines on each side of the body from front to back leg. They will eat a variety of insects, but harvester ants make up the bulk of the diet. Interestingly, harvester ant predation is limited at any one locale to prevent the ants abandoning the trail or nest - a typical harvester ant response to heavy, localized predation. Female Texas horned lizards lay 15 to 50 eggs in late summer with hatching following by fall. Hatchlings are just over an inch in length. This species is often encountered in river drainages in the state. The Texas horned lizard is the species best documented to shoot blood from its eyes - assumed to be a defensive measure.

Short-horned lizard (Phrynosoma douglassii)* is the most widespread of the species. It is found from western Nebraska to northeastern California and Durango, Mexico, to Alberta, Canada. Typically a mountain dweller, it inhabits territory from below 1,000 feet to over 11,000 feet in elevation. This is a small lizard, usually less than 4 inches snout to vent and 5 inches total length. The short- horned lizard has a single row of spiny scales on each side of the body from front to back leg, and as the name implies, the cranial horns are short. Three fourths of the diet is comprised of ants with other insects including grasshoppers and beetles rounding out the fare. The percentage of ants may be lower in more northern locales due to prey availability. Mating occurs in spring and 12 to 30 young are born alive in the summer. This is the only species of horned lizard to bear live young. Short-horned lizards are found throughout most of the mountainous regions of New Mexico and often incorrectly identified as a young Texas horned lizard or a large round-tailed horned lizard.

Round-tailed horned lizard (Phrynosoma modestum) is a small species seldom exceeding over 2 inches snout to vent or 3 inches total length. Males are usually much smaller than the females. The range of this lizard is from mid Texas to eastern Arizona and northern New Mexico to San Luis Potosi, Mexico, at elevations from 1,000 feet to 6,000 feet. This small lizard lacks the row of spines on each side of the body from front to back leg, and as the name implies has a rounded, rather than a flattened tail. Ants are the primary prey with both harvester and honey pot ants being consumed at a rate of almost 50 each day. Other insects round out this fare. They were at one time a common inhabitant of the West Mesa of Albuquerque and could be found actively feeding during mid-day. This lizard is usually colored much like the substrate it is found on with light sand coloring being very common. However, several color morphs have been reported, including a reddish pink individual seen by the author on the ridge west of Belen, New Mexico. About a dozen eggs are laid in early summer with hatchlings appearing in mid to late summer. Double clutches have been reported. This is a desert dwelling species well equipped for the extremes of temperature and lack of moisture found in North American deserts and is typically found in wind blasted gravel areas around washes and the sandy, grasslands of the state.

Regal horned lizard (Phrynosoma solare) is the rarest species in New Mexico and was long thought to inhabit only Arizona in the United States. It is found from the boot heel area of New Mexico to southwestern Arizona and mid Arizona to Sinaloa, Mexico, at elevations from sea level to almost 5,000 feet. This is a horned lizard similar in size and appearance to the Texas Horned Lizard with snout vent lengths of over 4 inches and a 2-inch tail. The crown of large cranial horns joined at the base, a single row of spines on each side of the body from front to back leg, and large spines on each side of the tail distinguishes this species from the Texas horned lizard. The regal horned lizard is more of an ant specialist than the other species with ants comprising over 90% of the diet. Active all year, a single clutch of 10 to 30 eggs is laid in mid summer with the young hatching about 2 months later. This is a desert dwelling species found from the lower foothills to the basins of the Sonoran desert.

Other U.S. Species
Coast horned lizard (Phrynosoma coronatum) is found from northern California along the western half of the state to the southern tip of Baja California at elevations from sea level to 6,500 feet. Endangered due to habitat destruction in much of its range, the Coast horned lizard looks like a smaller (3 to 4 inches in length) version of the Texas horned lizard. It has a similar double row of spines on each side of the body from front to back leg, but the large spines on each side of the tail distinguishes this species from the Texas horned lizard. This species inhabits sandy areas to scrublands and woodlands.

Flat-tailed horned lizard (Phrynosoma mcallii) is a sand dweller found in the restricted area in the Sonoran Desert around the lower Colorado River where Mexico, California, Arizona, and Baja California meet. This three-inch lizard is surely the fastest horned lizard, with speeds across the sand more in line with a fringe-toed lizard (Uma) with which it shares habitat. Identification is made easy with the long flat tail and a dark mid-dorsal stripe.

Desert horned lizard (Phrynosoma platyrhinos) is another small (2 to 3 inches) sand dweller found from southern Idaho to northern Baja California and northwestern Mexico, and central Utah to California at elevations from below sea level to 6,500 feet. There are two recognized subspecies: a northern desert horned lizard (Phrynosoma platyrhinos platyrhinos) and a southern desert horned lizard (Phrynosoma platyrhinos calidiarum). In appearance this species looks somewhat like the short-horned lizard with longer cranial horns and fewer body spines.

Closing Notes
This last species (desert horned lizard) is of particular note to members of the NMHS as one of our members has succeeded in breeding and rearing this species.... Loren and Dana Pennebaker have been successful in breeding and raising a number of different lizards. But a top achievement to date was a pair of desert horned lizards that laid eggs this summer that hatched after 45 days. The adults and young are fed on harvester ants that Loren and Dana (thanks to the Internet) are able to have shipped in - avoiding many long hours and severe stings hanging around our local ant nests. At 45 ants per day for each adult, that is a lot of ants. My thanks to Loren for the photographs he provided of his desert horned lizards that accompany this article.

Loren maintains his desert horned lizards in outdoor enclosures during the summer to take advantage of natural sunlight. At other times he uses ultraviolet B emitting light bulbs for the basking areas of the cages. Loren cannot work with the four horned lizard species found within the state due to their protected status. But as the pressures on this lizard increase and it may be that competent captive breeding efforts will eventually be required.

* Phrynosoma douglasii has recently been split into two species: P. douglasii and P. hernandesi. P. hernandesi is the species that is found in Colorado and points north. [CHS Editor]