Horned Lizards

All photgraphs, text and drawings © 2003 R. Joseph Collet, except as otherwise indicated by appropriate credit.

Click on the links below to view on-line abstracts of these articles written by R. Joseph Collet. At the end of each abstract, you will find either a link to the full article in Adobe pdf format or an e-mail link for requesting a copy.

Coming soon…

  • Platyrhinos in the Pinyons

  • Another Hybrid (2002), P. modestum /platyrhinos

  • The Problem with Short-horned Lizards in Xeric Environments

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An Experimental Outdoor Enclosure for Horned Lizards


In March of 1999, study and husbandry of horned lizards was resumed (at my new residence) in Washington County, after a hiatus of approximately 20 years. This research has enjoyed a unique benefit by being centered in an area not too distant from the approximate confluence of the Great Basin, Mojave, and Sonoran Deserts. The altitude at the enclosure’s location is about 2800’ (just 600 feet higher than the mean altitude for Las Vegas, Nevada—some 120 miles distant, for comparison, and accordingly, on a given day, is about 5° F cooler). Hence, it is reasonable to assemble a number of xeric species of Phrynosoma without seriously disadvantaging any of them.

Photo of a horned lizard

Altogether, 16 horned lizards representing 2 main species are currently under scrutiny. A grand piano-shaped outdoor enclosure comprising some 600 square feet houses them. A table follows setting forth certain data of interest for purposes of this presentation. Likewise, a scale drawing of the enclosure is appended for ease in following the full text of the presentation’s narrative. The author has maintained literally hundreds of lizards in terraria during his lifetime. The success of the present outdoor enclosure for maintaining numerous individuals in a healthy if not robust condition, merits special attention. Adequate shade, water, a variety of vegetative cover and more solid refuges, and a constant supply of several ant species which emerge from a natural-looking orifice, are what the author attributes to this accomplishment. Regular surveillance and neighborhood vigilance so far have discouraged natural predators and domestic would-be predators from destroying the subject specimens. In closing, it must be said that the horned lizards normal habits in relation to temperature and nightfall in this not completely natural setting, have likewise contributed to their well-being.

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A Better Way to Mark Horned Lizards for
Subsequent Re-identification


Toe-clipping, as a means to mark reptiles for population studies has been practiced for decades by herpetologist. In today’s information age, it has possibly become archaic. Brushing aside its possible compromising effects to individual animals, toe-clipping is neither fool proof nor very sophisticated. While it is unlikely that horned lizards, for example, of the same sex, relative size and coloration would be encountered in proximity of one another with an identical clipped toe configuration, one must not rule out the possibility of a previously unstudied lizard missing the corresponding toe due to natural causes showing up unexpectedly. Even less likely is the possibility of a purposefully marked individual—which is the subject of another scientist’s investigation—wandering onto a study plot, or the possibility of the subject scientist encountering a recently released reptile coincidentally missing a particular digit. It has been documented that horned lizards, in particular roam quite a bit as compared to other small lizards which seem to be more territorial. (Fair & Henke, Hodges, etc.). Often, looking at toes through field binoculars is difficult anyway, since sand usually covers one or more appendages on a given foot—requiring closer examination, in any event. Assuming the lizard can and will be captured anyway for weighing and measuring, and/or the extraction of blood, it would seem that a more reliable means of positive identification would be welcomed.

Image of a horned lizard on its back.

The insertion of fish line at the base of the tail to anchor colored beads has been suggested as an acceptable alternative, but strikes the writer as being unnecessary, as well as, potentially even more compromising to the reptile than toe-clipping. There have been reports of horned lizards getting hung up in dense vegetation (Brown) by their harnesses for transmitters, thus the suspicion is that beads and fish line could do likewise.

Invasive practices facilitating the insertion of foreign objects, such as, computer chips and transmitters, are yet another modality in the recited list of unnecessary methods for locating and identifying lizards. Just because super glue so far has been found to be adequate to close a wound (Milroy) to allow proper healing, it is difficult to assess the trauma to the subject both during and after such a surgery. Resultant stress and discomfort have not been scientifically measured to date for any of the above-named practices; therefore sensitive researchers should be aware of alternatives which not only do not expose the defenseless little Phrynosoma to such potential dangers. To some, these aforementioned practices further would seem to border on the inhumane, particularly in light of more sophisticated options being available which are unaccompanied by any of the aforesaid risks.

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Hydration (H20) Therapy for Phrynosoma


Image of two horned lizards licking water form one another's faces.

Water is assumed to be assimilated primarily from the insect prey upon which the xeric species feed, and secondarily, and irregularly from “rain harvesting” as discussed by Dr. Sherbrooke and observed by others. How much water is good? How much is too much and how little is not enough on a species by species basis?

Dozens of Phrynosoma platyrhinos during the course of preparation of this paper (1998-2000) have been “rescued” from busy thoroughfares and property about to be developed, or temporarily transported home for closer observation. In addition the writer has had experience with three other species (i.e., P. cornutum, hernandesi, and mcallii ), but more species need to be examined.

An experiment was designed to test water needs of several captive species. Not surprising, P. hernandesi relocated to the St. George altitude seemed to require more water than did the other species. Next in its ability to drink as a percentage of body weight appeared to be the hatchling cornutum followed by the platyrhinos (all ages) and finally the mcallii. Evidently, the species obtained from the higher altitudes progressively were able to obtain more water from sources alternative to prey, and may have built up a dependence upon it. A table in the discussion portion reflects these amounts and percentages. It is interesting to note that the subject hernandesi were collected at 8000’, the cornutum came from 4800’, the platyrhinos (mostly around St. George) from between 2000’ - 3000’ and the mcallii from about 200’-300’ above sea level. It will be interesting to correlate the tabular information with precipitation levels for each native area to formulate a hypothesis for wild individuals.

In the case of new captives dehydration and malnutrition seemed to go hand in hand, particularly for two P. platyrhinos captured during an expedition to Arizona (Yucca and Wickenburg areas, respectively). Appetites at the outset of captivity for these two were poor when compared to native caught P. platyrhinos. After rehydration both individuals resumed a healthier appetite and the large female gained about 25% of original body weight in 10 days time. Characteristically, it was likewise found that with platyrhinos hatchlings kept in indoor terraria, regular artificial rehydration stimulated appetite and was essential in order to foment growth and physical activity. In the case of P. hernandesi the writer attributes his recent success with their husbandry to the fact that each lizard is allowed to drink liberally from a hypodermic syringe every 2 - 3 days.

Lizards kept outdoors in a somewhat natural enclosure, although observed regularly lapping up water from the effects of sprinkler irrigation, readily accepted additional water from syringes, etc., when brought indoors for periodic weighing and measuring. Other factors need to be more closely monitored with wild individuals to be able to prove the aforestated tentative conclusions. Factors may include mean temperature, reproductive activity and food availability. And, based on the work conducted thus far, one must keep in mind the differences in individual species and the biophysical surroundings in which they are temporarily placed, contrasted with natural habitats.

In conclusion, whether the scientist maintains his or her specimens in an outdoor or indoor setting, it is very important to see that water is not only readily available, but that water intake is monitored conscientiously.

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Prey Preference in Phrynosoma, An Anthropomorphism?

Photo of a horned lizard


Amongst horned lizard experts it is commonly held that ants, primarily harvester ants (particularly, Pogonomyrmex spp., and [Vero]messor spp.), make up the main food source of all known Phrynosoma. Field studies, observation of captives, and examination of horned lizard scat have all lent credence to this notion, but the percentages being suggested in most articles unaccompanied by sufficient observation data may be more conjecture than fact. The bottom line is that simply too little published data exits. To examine this problem one must consider that:

  1. Different species of horned lizards vary in their numerical ant intake.
  2. Each horned lizard species may have contrasting feeding habits when comparing feeding behavior in the morning to that at dusk.
  3. Opportunism in foraging needs to be properly evaluated.
  4. A comprehensive correlation is lacking which compares data for hatchling, juvenile, sub-adult, and mature specimens, and importantly, based on the prey that is in their natural habitats and under average temperature and moisture regimes in which they exist.
  5. Variables such as periodic drought or excessive rainfall; latitude, longitude, and altitude; natural barriers like mountains and rivers which tend to isolate populations; need to be considered before arriving at definitive conclusions.
  6. The consideration of usually broad geographic distributions for even a single species, and the multitude of micro habitats therein supporting genetically distinct populations, must temper generalized, sweeping statements about prey preferences.

The writer commenced re-examination of the “ant specialist issue” by charting the precise arthropod consumption of three hatchling Phrynosoma platyrhinos through to first year hibernation (1999-2000), intermittent winter emergence, and final spring emergence to develop a provocative hypothesis, i.e., “Horned Lizards Generally Are Opportunists”. This tentative conclusion has been reinforced subsequently by observations of additional hatchlings indoors, and a number of adult captives (P. cornutum, hernandesi, mcallii, and platyrhinos), the latter in both indoor and outdoor terraria and in an outdoor enclosure simulating a typical habitat niche. Note: Albeit P. hernandesi studied were native to the mountains and consequently were forced to withstand a mid-desert backdrop, the impact of a potential humidity loss and risk of overheating were minimized by maintaining them within the aforesaid indoor, refrigerated air, microclimate.

Certainly horned lizards are myrmecophagus, but by no means exclusively so. Admittedly, the hypothesis needs to be tested further, but interestingly enough, all species were less anthropomorphic for ants than for other types of insects when are offered simultaneously.

Interpretation of the graphed data compiled thus far seems to suggest that quantities of certain food items ingested probably influences subsequent choices, both in the short run (a single feeding session), and what the horned lizard is hungry for at the commencement of the next day.

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A Study of Ten Horned Lizard Hybrids (P. mcallii / platyrhinos)


Hybridization has previously been reported amongst several species of Phrynosoma.

  • coronatum/ cornutum (in captivity, Baur 1999)
  • coronatum/ platyrhinos (in the wild, Milroy 1999, personal communication)
  • platyrhinos/mcallii (“suspected” in the wild, Rorabaugh / Stebbins 1979)
  • platyrhinos / mcallii (“suspected” in the wild, Young 1996 - 2000)
  • platyrhinos/ mcallii (in the wild, Poulin 2001, verified by personal observation same year by author of captive from amongst the living collection of the Tucson Sonoran Desert Museum)

  • Attempted mating has been observed in captivity between male P. solare and female P. cornutum (Collet 2001) and male P. cornutum and female P. solare (Baur 2001).

  • At least one photograph presented to the author by Baur pursuant to a visit to Sabino Canyon on the outskirts of Tucson, Arizona suggests the possibility of wild hybridization between P. solare and P. cornutum (although this is admittedly beyond the normal range for P. cornutum).
Photo of a horned lizard belly

Quite by accident the author came into possession of eleven hybrid platyrhinos / mcallii at the latter part of the summer of 2001 which he maintained indoors during the winter immediately following. Ten have survived until present (and since the end of April when released to the same outdoor enclosure described in his paper presented at the 4th Horned Lizard Symposium).

All were the product of a single P. mcallii female which laid two clutches of eggs separated by several weeks. Apparently, the offspring were fathered by more than one P. platyrhinos male. Remarkable differences in coloration, dorsal patterns and intensity of ventral flecking bear out this contention.

Certain exhibits consisting of dorsal photographs and belly scans document the foregoing. Additional data concerning diet and prey preferences, growth rates, hydration therapy, indoor hibernation, and clutch sizes/hatching dates are available upon request in the full text of the proposed paper from which this abstract is drawn…

To receive a copy of the entire article, please e-mail Joe Collet at colletjoe@charter.net.

What We Know About Phrynosoma solare, and What We Don't Know…


One of the largest Nearctic species of horned lizard is still somewhat of an enigma. There have not been many husbandry successes with the Regal Horned Lizard (Phrynosoma solare) in captivity. It’s true range is poorly understood. Its behavior has not been as well-documented as with that of other species. The Regal Horned Lizard’s territory within Arizona has been steadily shrinking due to development, but we are not certain what is happening across the border in Mexico. By contrast, much effort has been devoted to study and to enhance protection(s) for the Flat-tailed Horned Lizard (P. mcallii) which is clearly not fairing well under the present regime of man’s encroachment. Unfortunately, P. solare’s long-term destiny ultimately may not be too dissimilar unless more attention is paid to it now. During 2001, four adults (3 males and 1 female) were transported to an outdoor enclosure in southern Utah. Within two weeks of their arrival, an extremely aggressive behavior was noted by all males toward both sexes of Texas Horned Lizards (P. cornutum) that had already been brought-in the year before, and had successfully bred and them hibernated in the same enclosure. No such aggression was observed toward any of the 3 other species sharing the enclosure.

What We Know

P. solare

Photo of P. solare
  1. Is one of the largest Nearctic horned lizards
  2. Is oviparous
  3. Has not been recorded to have crossbreed with other species of Phrynosoma
  4. Is not strictly myrmecophagus
  5. Is found in the USA and Mexico
  6. Inhabits desert often in association with the Saguaro Cactus (Cereus giganteus)
  7. Is a “blood-squirter”
  8. Will sun itself on asphalt highways where it is vulnerable as a road kill victim
  9. Enjoys a unique morphology
  10. May be captured and possessed pursuant to a small game hunting license in Arizona

To receive a copy of the entire article, please e-mail Joe Collet at colletjoe@charter.net.

Is There Intelligence in Cnemidophorus?

Photo of a Whiptail Lizard in a human hand.

Synopsis / Abstract:

Remarkably, Whiptail Lizards seem to be able to remember individual humans, and lose their fear, accordingly, in response to food rewards. Experiments thus far with formerly wild, now captive Cnemidophorus tigris and Cnemidophorus velox have borne out a remarkable ability to recognize one human from another, and to develop a certain trust at being handled in connection with feeding time.

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