Tales From The Ranch: Introducing Pogonomyrmex barbatus

Harvester ant mound

As mentioned in the past, I love torturing my Brit friend Dave Hutchinson with horror tales about the fatal fauna and flora of Texas. He’s already convinced that Texas is nothing but a semi-desert version of Peter Jackson’s Skull Island spider pits, where every last animal and plant in the state exists solely to eat us, enslave us, and steal our wimminfolk. This, coming from a man who lives in a country overrun with hedgehogs, starlings, sparrows, and Manchester United fans. Some people just don’t know when they have it worse than everyone else.

I’ll admit that some of our problems lie with misidentification, as well as exceptional expectations on the lethality of our wildlife. When I first moved here, my previous experiences with ants were as minor pests, but not anything that could inflict serious damage before stripping the meat off my bones. I’d heard about Argentine fire ants, but decent forms of identification were lacking, especially to schoolkids from out of state. One day, standing out in a big cleared patch of ground near a highway, I found myself being stung repeatedly by giant red ants, and those ant stings swelled and came to a head full of clear fluid after about two days of rather intense pain. Not knowing any better, I’d come across fire ants, right?

The reality was that I’d come across a mound of our indigenous harvester ants, Pogonomyrmex barbatus, and I was paying for standing right in the middle of the mound. I also got off lucky, as I only had about six stings. Argentine fire ants, when they sting, sting in the dozens. P. barbatus also pretty much inflicts enough damage as necessary to convince big dumb vertebrates to get the hell out of their nesting sites, and they otherwise leave humans alone. Fire ants, though, actively hunt around and in human habitations, nest in phone junction boxes and other electrified areas (for some reason, they’re attracted to electrical fields, so they’re commonly found chewing on the insulation of ground-installed spotlights and water sprinkler controls), and make lawn mowing into an endurance sport. If Dave ever discovers that they react to flooding by forming huge living rafts and balls that allow the ants to flow by the thousands onto any life form that comes in contact with them, he’ll be catatonic for weeks.

Harvesters, though, are positively mellow by comparison. They get their name from their tendency to collect grass seeds and bring them back to extensive granaries within their nests, and the granaries are large enough that the nests can extend for meters below ground. At the beginning of each year, most nests are only noticeable because the ants shred and prune any vegetation growing within the vicinity. By the middle of the summer, continued construction leaves a very distinctive pile of small stones around the nest entrance, resembling nothing so much as a very small volcanic crater. Finer dust is moved further away, and larger rocks worked around, so the stones generally range from about the size of a typical ant’s head to stones just large enough to be moved by two or three ants working in a team. Throughout North Texas, they’re usually our distinctive and ubiquitous ironstone, but occasionally such treasures as fossil mammal teeth can turn up in the mound spoils. I myself haven’t found anything other than the occasional tiny shark’s tooth in local mounds, but I also haven’t been looking that hard.

Harvester ant - closeup

Since I know that Dave will insist upon knowing why such abominations walk the earth, I’ll also note that harvester ants are a vital food source for many small animals, particularly the Texas horned lizard (Phrynosoma cornutum). In fact, P. cornatum pretty much eats only harvester ants in most circumstances. Sadly, the horned lizard and the harvester ant are threatened by the same two organisms: fire ants and humans. Fire ants do a great job at hunting down and devouring horned lizard nests, thus partially explaining why they’re becoming threatened throughout Texas, but both lizards and harvester ants suffer more from habitat destruction and random pesticide application. In the process, harvester ant mounds become more and more rare, generally turning up in undisturbed areas such as those at the ranch. The horned toad…well, I haven’t seen a live one outside of a zoo since 1980.

Harvester ant - close closeup

Another aspect of harvester ant behavior led to a very interesting observation this last weekend. While harvesters have no interest in human habitations as food sources, they definitely appreciate any sources of water, human-caused or otherwise, that last through the summer. They march impressive distances to any steady water source, whether it’s from a natural seep or a leaking pipe, so long as the water is reasonably clean. When I first moved to Texas, I lived in the center of a large area cleared for construction of a new housing subdivision, and I came across a minispring formed by a leaking water line in the middle of the construction zone. Every morning, harvesters rushed out to collect as much water as they could get before the sands around the “spring” became too hot, leaving them open to predation from birds and the occasional spider. The few casualties they faced by becoming bird food was apparently worth the effort of having a water source both closer and cleaner than the nearest creekbed, and they kept coming up to the day a house was built atop that water line.

This weekend, I was reminded of that tiny spring when watching the behavior of multitudes of leopard frogs (Rana pipiens) around a seep close to the Brazos River. The whole area around the ranch was just starting to dry out after a series of rains, so I understood why so many frogs would be up away from the river itself. What didn’t make sense at first was why so many would be in such a shallow and honestly piddling puddle, until I stopped to take a closer look. The frogs had no interest in the seep for either residence or breeding, and all of the frogs were too small to breed in any case. However, it was irresistible to harvester ants, which piled up against each other while gathering water. The frogs just waited for the ants in the seep, ate their fill, and went back to the river. Confirmation came in finding frog scat, almost bejeweled in harvester ant carapaces, all over the area. Once the rains stop, the seep dries up, the harvesters find another well, and the frogs find other food sources. In the meantime, the frogs are fat and sassy, and the harvesters aren’t hunted to the point where they move elsewhere for their water. And the cycle continues.

–And a tip of the hat to Bug Girl, who regularly reminds me about the constant interaction between insect and flowering plant, and the odd stories therein. Go read every last post she ever wrote, and don’t be afraid to offer her a job if you’re in need of a professional entomologist.

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