Horned Lizards and Ants

Image of Horned Lizard

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 Ant

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.

Horned Lizard Eating an Ant

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.

Juvenile Horned Lizard

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.

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About aneyefortexas

Retired writer/teacher/photographer, now photographing the Chihuahuan Desert at the Big Bend Ranch State Park, Texas.
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8 Responses to Horned Lizards and Ants

  1. Ann Mayo says:

    Very nice story and photos. I study harvester ants in the Fort Worth, Texas area and present my work to a variety of audiences, including public groups and university students. Would it be possible to include Patrick Berden’s photo of the horned lizard about to eat an ant in my presentations? I would give full credit. Thanks for your consideration.

  2. Mick says:

    I would like to point out a couple of technical inaccuracies. Harvester ants are in fact quite a nutritious food for horned lizards, not a poor one. Their seed based diet is very nutritious, but each worker contains a relatively small amount of nutrients in its gater. The exoskeleton is not digested by design, because it is made of a polysaccharide called chitin, which is non-protein nitrogen source, and doesn’t add to nutrition. The nutrients of the harvester ant is contained in the gaster of the ant. These nutrients are miscible in bowel secretions, and are washed out during digestion, leaving a dessicated exoskeleton.

    Harvester ants are not solely preyed upon by horned lizards. Other lizards are known to partake of them in limited numbers, as are occasionally birds, and other invertebrates. Neither do horned lizards prey upon harvester ants exclusively for as a food source. Harvester ants merely make up the bulk of the horned lizard diet (60-90% by horned lizard species).

    There are also many species of harvester ant that horned lizards prey upon, not one. There are actually some 28 or more species and subspecies of harvester ants in the Pogonomyrmex genus, and there are several different species spanning from Florida to California, and up into the NW and high desert. From P. badius, to P. occidentalis, and P. californicus. Some horned lizards in the high desert also partake heavily of a completely different genus quite readily, the Honeypot ant.

    I’m not sure your source, but as an experienced reptile rehabber most known for my work with native venomous snakes, horned lizards, and harvester ants, I would have to disagree with the assertion that harvester ants possess the most toxic venom of any animal in the new world. It has been reported that the sting of a single species, that of the Pogonomyrmex maricopa (in Arizona) was rated among the most painful stings. That doesn’t necessarily mean “most toxic”. It is also not really true that a single sting kills several mice. My research sources state that .12mg/kg, or equivalent of 12 stings from P. maricopa, was enough to kill a 2kg mammal. You could make the case that this breaks down to several smaller mice per sting, but that’s not really the way that it was researched, and in fact, it’s never been replicated in any other research paper to my knowledge. Nonetheless, a sting from Pogonomyrmex is quite painful, and I have been stung many times.

    There is also no hard evidence that I have seen of horned lizards possessing any blood factor to give immunity. This is theory, but has never been identified as far as I know, and I pretty well stay on top of this kind of news. The horned lizard is not the only reptile which is resistant to harvester ant stings either. Similar research conducted in other native species of lizard, namely Sceloporus olivaceus, has shown that harvester ant venom is several hundred times less effective against them as for mammals. The data indicates that harvester ant venom is more so evolved as a defense against seed foraging rodents, than against reptiles, therefore, it may not be accurate to state that the horned lizard has “immunity”, as opposed to saying that harvester ants have venom tailored against a different species entirely.

    Thank you,
    Mike C.

    http://wichitafallsreptilerescue.webs.com

    Reptile rehabilitator, Texas DSHS certified animal control instructor (reptiles), author “The Horned Lizard Manual”, 11 years captive and rehabilitative experience with horned lizards of 5 species, and a distributor of Pogonomyrmex barbatus harvester ant feeders for ant farms and horned lizard food.

  3. Pingback: Horned lizard | Goldengateconsultancy

  4. Margarethe says:

    Excellent photos and well-written text focusing on interesting content – great blog!

  5. David C. says:

    Thanks for the amazing background on one of the great desert reptiles. So that;s what eats harvester ants? We had a few swarms of them near the house, and they needed their predator handy.

    A book I picked up recently in Austin reminds me of your blog’s depth and topic, “Remarkable Plants of Texas”; you might like it.

  6. Such a wonderful story/lesson through the web. When I think of all the wasted time through silly meaningless blogs! Thanks for the excellent information and photos.

  7. Patrick Berden says:

    Thanks for the honor of contributing to your very nice blog. It was a fantastic experience to visit your part of the country. I wish those Thexas Horned Lizards lived over here. Be careful with them!

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