Horned Lizards

Not Horney Toads

         

There are 14 species of horned lizards, 8 of which will be found in continental North America, and 6 other species restricted to Mexico. Most have been around for at least a million years, and one, the pygmy short-horned lizard restricted to the higher elevations of the Pacific Northwest, for 15 million years. Over such a long period of time these adaptable animals have developed some amazing characteristics; for instance, the majority of their species lay eggs, but 4 give birth to live young (added internal incubation protection from the cold at higher elevations.) Then there is that famous adaptation of squirting blood from their eyes when attacked by canine predators such as foxes and coyotes. Only four species actually do this and, unfortunately for a good story, our desert one does not.

It has been pointed out by Eric Pianka and Wendy Hodges, lizard researchers at the University of Texas, that if we look at the interrelationship of horned lizard anatomy, behavior, diet, daily activity patterns, temperature regulation, and reproductive tactics we will discover a beautiful and tightly woven ecology. Let’s do it, especially since they have provided a very nice diagram to help us see what is going on.

 Horned lizards live in areas where food supplies can be very patchy; to counter this they have specialized on ants, although some are more faithful to this diet than others. Ants contain much indigestible chitin, which require the lizards to carry around lots of ants in a large stomach—the largest of any lizard in relationship to its body size, including the desert iguana. This large stomach slows them down so they have developed ‘crypticity’, the ability to blend into their surroundings to a high degree. In fact, their abilities are so plastic in this regard that it is difficult to use color or pattern to identify a species. (The best method is to use the horn pattern on their head along with the known distribution of each species. See below.) When body pattern blends in with the background, movement destroys the protective advantage, so these lizards move slowly and freeze often. Notice this next time you see one. It will freeze in the open and then quickly run into the shade of a bush.

And why those remarkable elaborate horns on the lizard’s body? They are very effective at protecting them from predators. Snakes and birds have been found dead with lizards’ horns projecting through their throats. Horned lizards can also inflate their bodies with air, like puffer fish, becoming an armored mouthful. Recent research demonstrated that flat-tailed horned lizards with the shortest horns at the back of their head were more apt to be taken by loggerhead shrikes than those with longer horns.

Because the horned lizard is well protected through its armor and coloring, it can get away with having a large stomach and slow movements, which, in turn, allows it to eat ants, which have little nutrition but, since there are so many of them, they add up to enough. Read that again. And finally, the large body cavity allows for large clutches of eggs to develop and the many offspring compensate for a high predation rate.

Horned lizard species are threatened across their range from urban expansion and invasion of their habitat by the Argentine ant.  They do not make good pets, dying slowly without their natural food. Never take them from the wild. Consider landscaping that allows for the natural plants and animals to thrive. Take pictures.