The horned lizard, aka horny toad, uniquely adapted to its desert home

Horned lizards are part of our Nevadan heritage. Mark Twain mentions them in his book, "The American West," the Western Shoshone noted the presence of horned lizards as spiritually significant, and these lizards are commonly depicted in American Indian artwork and pottery.

We now find horned lizards on logos of outdoor clothing, as stuffed animals in stores, and as artwork in local craft fairs. But the most amazing thing is to view them in the wild, in their natural habitat.

I am one of those rare children who knew exactly what they wanted to be when they grew up – a herpetologist – which literally means, “to study creeping things.” My love for herps (short-hand for reptiles and amphibians) led me to grad school where I studied Phrynosoma, the genus that includes all horned lizards.

Hardy lizard suited to high desert 

In order to understand lizards, we have to first understand who they are. Most importantly, they are poikilotherms. Poikilotherms are organisms that cannot regulate their body temperature except by behavioral means, which is why you will find lizards sunning themselves to warm up, and hiding under shrubs to cool down. This need for heat also explains why most lizards are found within desert environments, and nearly absent from high latitudes and elevations.

However, horned lizards are an exception; for they can be found at high altitudes and latitudes, where the growing season is short and temperatures are cool. It is from this that we can see how horned lizards have become so uniquely adapted.

A major theme we always remind our students is the inherent link between form and function. When inspecting a horned lizard, you will notice their reduced mandibles, short teeth and large stomachs. And, we know that all of these structures are involved with eating (something I love as well), which means that horned lizards must have a unique diet: harvester ants.

This is an unlikely food source, since harvester ants create formic acid when threatened, which is toxic to predators. Horned lizards have no issues capturing these ants given their very sticky tongues and a dense film of mucous lining their mouths that prevents the ant from biting the lizards as they are swallowed. However, ants are a nutrient-poor food source and contain much indigestible chitin, so horned lizards must eat hundreds on a daily basis. This requires a large stomach for digestion, hence their obese toad-like body shape and the nickname “horny toad.”

With their pancake-shaped bodies covered in spinous armor and petite legs, horned lizards move like a Sherman tank – slowly, precisely and with purpose. By no means would you look at them and think “athlete,” and you would be right, as horned lizards can only spurt short distances. Instead, they rely on cryptic coloration to blend into their surroundings.

If cornered by a predator, they will gulp air and inflate their bodies to appear larger. However, if caught, horned lizards will thrash their heads to stab the predator with their cranial horns.

A last-ditch effort in some horned lizard species includes squirting blood from their eyes. Their blood is distasteful to canine predators, due to toxic compounds sequestered from the harvester ants they eat. The three species found in northern Nevada can squirt blood, but it is uncommon.

If we consider the morphology and behavior of these curious lizards, then it becomes easy to see their vulnerability to human activities: invasive fire ants (which drive out the native harvester ants, and are inedible to lizards), habitat degradation, and collection for the pet trade. All these have caused horned lizard numbers to dramatically decline.

While hiking in Northern Nevada, Cecilia and I have had the opportunity to observe the three species that reside here: the desert horned lizard (Phrynosoma platyrhinos), the greater short-horned lizard (P. hernandesi), and the pygmy short-horned lizard (P. douglasii). All three are adapted to living in arid environments; for example, they will curl their tails over their heads and divert water to their mouth during those rare times it rains. This is known as rain-harvesting.

These horned lizard species have adapted to high elevation, cold deserts such as Northern Nevada’s Great Basin. For instance, all three of Northern Nevada’s horned lizards give birth to live young, known as viviparity. This helps the mother control the temperature of the fetuses to increase their growth rate, and thus have better chances to survive in environments with relatively short growing seasons and cooler temperatures.

So the next time you are hiking and see one from the corner of your eye, take a moment to pause and observe their behaviors and adaptations from a distance, and relish in the thought that you just seen a horny toad!

Dr. Cecilia Vigil, DVM, and Dr. Megan Lahti, PhD, are biology instructors at Truckee Meadows Community College and enjoy sharing their explorations of Northern Nevada's natural history.