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Texas Horned Lizard (Phrynosoma cornutum)

 

[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column][/vc_row][vc_row][vc_column width=”1/2″][vc_single_image image=”1290″ img_size=”large” alignment=”center” style=”vc_box_rounded”][vc_column_text]Texas Horned Lizard, Cochise Cnty, AZ. Photo by Jim Rorabaugh[/vc_column_text][/vc_column][vc_column width=”1/2″][vc_row_inner][vc_column_inner width=”1/2″][vc_single_image image=”1890″ img_size=”medium” alignment=”center” onclick=”img_link_large”][vc_column_text]Texas Horned Lizard, Cochise County, AZ. Photo by Jim Rorabaugh[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][vc_column_inner width=”1/2″][vc_single_image image=”1889″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Texas Horned Lizard north of Mescal, Arizona. Photo by Roger A. Repp[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][/vc_row_inner][/vc_column][/vc_row][vc_row][vc_column width=”1/6″][/vc_column][vc_column width=”2/3″][vc_column_text]

Description

When most herpetologists think of Tucson, we think of the Sonoran Desert, or the Sky Islands that rise up from the desert floor. But our great herpetological diversity results from the Chihuahuan Desert as well. This grand desert, the largest in North America, includes the Rio Grande Valley, much of southern New Mexico, western Texas, and eastern Mexico well down towards Mexico City. But the Chihuahuan Desert also stretches west into Arizona, and many of the reptiles and amphibians associated with it can be found around Tucson.

The Texas Horned Lizard (Phrynosoma cornutum) is one of these Chihuahuan species that occurs just east of town. The largest and most colorful of Arizona’s six species of horned lizards, it is distinguished by large dark dorsal blotches surrounded by white, twin dark stripes radiating from each eye, and a prominent white stripe running the length of its back.

All of the horned lizards seen in the city of Tucson are Regal Horned Lizards (Phrynosoma solare), but most of the other Arizona species are not far away. For example, the Greater Short-horned Lizard (Phrynosoma hernandesi) is found in all of the nearby Sky Islands, just above the desert floor, while the Desert Horned Lizard (Phrynosoma platyrhinos), a Sonoran Desert species, is (or was) found in valley bottom areas west of town.

Description and Natural History

The Texas Horned Lizard reaches up to 5 inches (130 mm) in snout-vent length and is “particularly flat” (Brennan and Holycross, 2006). Like the Regal Horned Lizard, it has long spikes at the back of its head, two of which protrude beyond the others. Unlike the Regal, the horns do not touch each other at the base. It is hard to confuse this species with any other horned lizard due to the long spikes (the name cornutum means horn in Latin), prominent colors, and large size.

Not surprisingly, individuals of this species eat ants. Various studies have looked at how large a percentage of their diet is made up of ants, and the results indicate that it can be high (up to 85%) but is often lower. Pianka and Parker (1975) examined 351 individuals and found that ants were 69% of frequency and 61% of volume in the diet, but they also eat a variety of beetles, grasshoppers, and other insects.

Texas Horned Lizards lay eggs, up to about 50 per clutch, and hatchlings in this part of the country are first seen in June through September (Ballinger 1974, Degenhardt et al. 1996). Like many horned lizards, they can squirt blood through their eyes, an interesting anti-predator behavior (Sherbrooke and Middendorf, 2001). Price (1990) presents a comprehensive overview of the biology of this species.

Distribution near Tucson

Texas Horned Lizard territory lies beyond the gateway between the Rincon and Santa Rita mountains where the elevation rises, the Sonoran influence tapers off, and the Chihuahuan influence begins. Records of this species on the western edge of its range are not common in this area, but for the past few years a number of us have stopped to look at horned lizards whenever we can and have been rewarded for our effort.

At 1710 h on 19 September 1997, one of us (Roger Repp) photographed a P. cornutum one mile north of Mescal, Arizona, in Cochise County (Fig. 1). Mescal is the small town north of 1-10 before the highway descends into Benson. At 1637 on 7 June 2006, two of us (Kevin Bonine and Don Swann) observed a P. cornutum north of Mescal on the road into Happy Valley, on the east side of the Rincon Mountains. This lizard was located approximately 0.5 miles north of the turnoff to Old Tucson Studios east, and we shot a large number of photos of it before releasing it (Fig. 2). Our observations are not historically unique, but are close to the extreme western records of P. cornutum in Arizona. Maps in Price (1990), Brennan and Holycross (2006), and Stebbins (2003) show the species range just touching Pima County (south of Tucson, the species also reaches into eastern Santa Cruz County). Robert Bezy (personal communication) collected a voucher specimen (UAZ 56020) from the Mescal area, and Klauber (1939) recorded it from nine miles west of Benson (very near Mescal and the Pima County line). During a recent inventory of the Whetstone Mountains, the species was found only on the eastern side of the range (D. Turner, personal communication).

P. cornutum thus has a place in the interesting biogeography of herpetofauna in the 100-mile circle around Tucson. As noted, most of the range of the species is to the east in the Chihuahuan Desert of New Mexico and Texas. P. cornutum shares the western edge of its range with several other species associated with this desert, including the Mexican Hognosed Snake (Heterodon kennerlyi) and the New Mexico Threadsnake (Leptotyphlops dissectus), which also apparently occur just east of Tucson, but not in town. A few other species associated with the Chihuahuan Desert, such as the Great Plains Skink (Plestiodon obsoletus), do occur widely to the northwest of Tucson and one species, the Desert Box Turtle (Terrapene ornata), may range west into the Tucson Basin – but that is a complicated story to be told another day.

In the case of the Texas Horned Lizard, we are not aware of any records closer to the east side of Tucson than Mescal. It surely would be interesting to know whether this species slips into Cienega Creek or the Rincon Valley, or even if it is found further north along the San Pedro River.

Remarks and Conservation

The first Texas Horned Lizard specimen known to science was apparently collected by Lewis and Clark and brought to President Thomas Jefferson (Degenhardt et al., 1996). Wade Sherbrooke (1990) observed this species drinking during rainstorms in a unique way, by arching the back and allowing water to drain through channels between the scales directly into the mouth. Texas Horned Lizards enjoy no special status in Arizona except that, like all horned lizards, they cannot be collected and sold into the pet or curio trade. The species has been introduced widely on the east coast, and populations have persisted in Florida and South Carolina for decades (Price 1990). Texas Horned Lizards seem to be doing well in southeastern Arizona, though valley development east of Tucson is no doubt affecting their habitat and will continue to do so. However, this species is declining in significant portions of its eastern range, at least in part due to the invasion of the introduced red fire ant (Price, 1990).

Literature Cited

Ballinger, R.E. 1974. Reproduction of the Texas Horned Lizard, Phrynosoma cornutum. Herpetologica 30:321-327.

Brennan, T.C., and A.T. Holycross. 2006. A Field Guide to the Amphibians and Reptiles in Arizona. Arizona Game and Fish Department, Phoenix. 150 pp.

Degenhardt, W.G., C.W. Painter, and A.H. Price. 1996. Amphibians and Reptiles of New Mexico. University of New Mexico Press, Albuquerque. 431 pp.

Klauber, L.M. 1939. Studies of reptile life in the arid Southwest. Bulletin of the Zoological Society of San Diego 14:1-100.

Pianka, E.R., and W.S. Parker. 1975. Ecology of horned lizards: a review with special reference to Phrynosoma platyrhinos. Copeia 1975:141-162.

Price, A.H. 1990. Phrynosoma cornutum (Harlan), Texas Horned Lizard. Catalogue of American Amphibians and Reptiles. 469.1-7.

Sherbrooke, W.C. 1990. Rain-harvesting in the lizard, Phrynosoma cornutum: behavior and integumental morphology. Journal of Herpetology 24:32-302.

Sherbrooke, W.C., and G.A. Middendorf. 2001. Blood-squirting variability in horned lizards (Phrynosoma). Copeia 2001:1114-1122.

Stebbins, R.C. 2003. A Field Guide to Western Reptiles and Amphibians. Houghton-Mifflin Company, Boston. 533 pp.

Authors: Don Swann, Roger Repp, and Kevin Bonine

Originally published in the Sonoran Herpetologist 2007 20(8):80-81

For additional information on this species, please see the following volume and pages in the Sonoran Herpetologist: 2011 Oct:93-106.

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