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Science & Health

In polite society the horny toad is known as the Texas horned lizard. In the scientific world, the reptile is referred to as Phrynosoma cornutum.

But fewer people are referring to the dinosaur-looking creature at all, since it began to disappear from Texas backyards over the past few decades.

Forty years ago, the horny toad was generally found across most of the state; the only part of Texas where it was not common was the Piney Woods of East Texas.

Horned lizard

The horned lizard's color varies with the geographic location.

After the 1950s, however, its range began to recede to generally west of a line from Fort Worth through Austin and San Antonio to Corpus Christi on the Gulf Coast.

A 1993 study report done by the Texas Parks and Wildlife Department says that no single reason can be given for the decline, but the report concludes that the horned lizards have decreased in numbers and been reduced in range from previous years when they were common as far north as Kansas and as far east as southwestern Missouri.

The lizards are usually from 3 to 5 inches in length. Their color varies from brown to tan to gray depending on the geographic location.

Scientific observation of horned lizards began in this country in the early 1800s with the help — like much research of the period — of Thomas Jefferson.

According to an article for the Catalogue of American Amphibians and Reptiles by Andrew H. Price, who also headed the TPWD study, the American statesman was responsible for procuring the first specimen through explorers Lewis and Clark. Jefferson brought the specimen to the Museum of the Philosophical Society of Philadelphia.

As decade-by-decade scientific observation of horned lizards continued, the species’ numbers in the southwestern United States seemed to peak around the 1950s or 1960s. In the last two decades the decline began to be noticed and documented.

The TPWD study of the early 1990s used questionnaires distributed by various means about sightings and also used devices to capture some of the creatures. (The report points out that certain questionnaires that claimed sightings of horny toads in excess of ten inches in length were discounted.)

A sighting study is continuing at Chaparral Wildlife Management Area, about 60 miles north of Laredo, near Cotulla. There, TPWD observes the lizards and their habits with the help of convicts from the Texas prison system.

Fire ants (Solenopsis invicta) are sometimes cited as a culprit in the ecology of the horned toad. There is a correlation in parts of Texas where the fire ants appear and the horned toads disappear. However, there seems to be a decline in the numbers of horned lizards in the Panhandle, where fire ants have not appeared.

If the fire ants are partly responsible for the changes, the survey says, the reason may be the disappearance of the smaller harvester ants (genus Pogonomyrmex) when fire ants move into an area. Harvester ants are a food source of the horny toads, as are grasshoppers and beetles.

Other possible threats to horny toads are pet collection, road kill and urbanization. The TPWD study concludes, however, that there is less danger from urbanization than from farming.

The tilling of the earth — plowing — shows up in the survey as suspect number one. It seems the horned lizards hibernate and lay their eggs underground during the winter and summer respectively. Plowing disturbs that process.

Also, the conservation researchers caution that in recent decades pesticides and defoliants have become more common for machine harvesting. So, they say, chemical use cannot be ruled out as also having some possible effect on the decline of the horny toad.

TPWD conservation scientists believe that South and West Texas will continue to have substantial populations of horned lizards. In other parts of the state, such as the coastal prairies southwest of Houston and in the Panhandle, the numbers will probably continue to decline. The area inside the triangle from Dallas to Houston to Austin may have seen the last of the horny toad.

To help preserve the horny toad, the conservation scientists recommend the introduction of vegetation corridors through the more developed and cultivated parts of Texas. They recommend control of fire ants as well.

— written by Robert Plocheck for the Texas Almanac 1996–1997.