Horned Lizards and Ants

Horned Lizards Are Survivors from the Age of Dinosaurs. Photo courtesy Tom Spinker ~ All Rights Reserved

If you look at them closely, you could almost imagine that the Texas Horned Lizard is really just a miniature dinosaur, and you wouldn’t be far wrong. This creature is a true survivor of the age of dinosaurs. And throughout the millennia, it has been locked in an adversarial relationship with the Harvester ant, another survivor from ancient times. Their relationship is one of predator-versus-prey. Texas Horned Lizards have become specialist feeders, living almost exclusively on Harvester ants, an unusual preference. In response, Harvester ants have developed specialized defenses so ferocious that nothing else can eat them.

Harvester Ants are the Horned Lizards Primary Food Source

You would think that Harvester ants would be easy prey. Their colonies are large, they live in one spot for decades, and they forage during the day. But appearances can be deceiving. Harvester ants are exceptionally poor food. Their indigestible exoskeletons make up much of their total bulk and there’s not much value in the remaining flesh. Any predator that hopes to survive by eating ants has to eat a lot of them just to make a meal.

This Horned Lizard is catching an ant on its sticky tongue. Photo Courtesy Patrick Berden ~ All Rights Reserved

Horned Lizards have managed this poor diet by becoming very unlizard-like. For one thing, they’ve become rather sedentary, spending most of their feeding time hanging out around ant beds and gobbling up as many as they can hold. And they can hold a lot of ants – their stomachs are over 65 percent bigger than those of any other lizard. In fact, the Horned Lizard’s flat, wide shape is a direct outgrowth of its giant stomach.

Horned Lizard's broad, flat bodies have plenty of room for their large stomachs

Harvester ants have developed their own specializations in response to these predations. For one thing, they’ve learned to keep the young, protein-and-fat rich workers in the lower part of the nest where they raise brood, tend to the queen, and process food. As the workers age, their body reserves shrink. When they are old and thin, they move to the surface and become members of the foraging force. As a result, the ants on the surface are so nutritionally poor, other predators can’t eat enough of them to survive.

Being not much worth eating is a unique specialization for ants, but the ants have another powerful specialization to call on – their venom. During the ongoing war with the lizards, Harvester ant venom has become the most lethal known venom of any animal in the New World! This extraordinary venom contains many toxic substances, but the most powerful is a potent “hemolysin” which destroys red blood cells directly; it is so effective that a single Harvester ant bite is enough to kill several 20 gram mice.

Yet the Horned Lizard remains unfazed by all this, for its’ red blood cells contain specialized factors that protect it from the Harvester ant’s poison. The Horned Lizard is the only reptile that has this blood factor, and it is the only creature that is completely unharmed by the Harvester ant’s sting. The specialization is even more remarkable when you consider that one species of lizard eats only one species of ant; conversely that ant’s only predator is that single species of lizard. And so the struggle continues – the ants growing ever more toxic and the Horned Lizards growing ever more resistant to the ant’s poison. Theirs is a remarkable example of the many and diverse relationships that exist among the inhabitants of the great Chihuahuan desert.

Advertisement