Nature Notes | Arachnid among the Ants

Photograph by Paula Cushing. Twenty years after they discovered it south of Marfa, scientists are now unlocking the secrets of the “Texas Mystery Spider.”
Photograph by Paula Cushing. Twenty years after they discovered it south of Marfa, scientists are now unlocking the secrets of the “Texas Mystery Spider.”

Arachnid among the Ants: The Saga of the “Texas Mystery Spider”

By Andrew Stuart

In 1938, the artist Alexandre Hogue – a member of the so-called “Dallas Nine” – created one of his most famous West Texas paintings, called “Mother Earth Laid Bare.” It’s a resonant title. In open deserts and prairies, in rugged badlands, the Earth’s bedrock realities are visible here. The very bones of the planet are exposed.

But this land conceals as much as it reveals. Unknown creatures flourish in its recesses, or under cover of desert night. There’s no better example than Myrmecicultor chihuahuensis, the “Texas Mystery Spider.” Its discovery two decades ago launched an international scientific journey. And now, researchers are gaining surprising – if grisly – insights into this tiny Chihuahuan Desert creature.

Arachnologist Norman Horner is professor emeritus at Midwestern State University, in Wichita Falls.

“I’ll be 81 my next birthday,” Horner said, “and I never thought 20 years ago that I’d still be chasing these spiders. But, hey, it’s fun.”

And though he’s retired, he travels regularly to the university’s Dalquest Desert Research Station, on the Presidio-Brewster county line south of Marfa. It’s ground zero for the “mystery spider” saga.

It began in 1999, when Greg Broussard, one of Horner’s students, was using “pitfall” traps to collect and catalog Dalquest spiders. At first, he found the usual suspects. But then Broussard encountered a spider – less than 3 millimeters long, and nearly translucent – that stood out. The patterning of its eight tiny eyes was unique, and unfamiliar.

“And when he tried to identify it, he couldn’t identify it,” Horner said. “And he wanted me to help him, and I couldn’t identify it. And so I sent it to a colleague at Texas Tech. He couldn’t identify it. It went from there to the California Academy of Science. The spider taxonomist out there couldn’t identify it either.”

The spider was ultimately sent to the American Museum of Natural History in New York, to the desk of Norman Platnick. Platnick, who died in 2020, was the world’s foremost spider taxonomist. He too was flummoxed.

“When he looked at it,” Horner said, “he said, ‘I don’t know what it is. And I really have my doubts that it came from North America.’ I assured him that it did. So he wanted to build a group of people to see if we could go out and find it.”

Horner and Platnick took a team of experts to Dalquest. They found one more “mystery spider.” But the creature’s ecology and behavior remained a blank slate.

Then, in 2008, 200 miles south of Dalquest, there was a break in the case. David Lightfoot, of the University of New Mexico, was doing research at Cuatro Cienegas, in Coahuila, Mexico, when he encountered the mystery spider. He found it atop a familiar desert sight – the broad, gravelly mound of a harvester ant colony.

Armed with this association, Horner returned to Dalquest to set traps near ant nests. He caught 140 specimens. The spider has now been found in association with three Chihuahuan Desert harvester ant species.

These ants “harvest” seeds and other plant material, and store reserves in special chambers, for the colony’s winter needs. Those reserves attract opportunistic “guests” – beetles, crickets, tiny arthropods like silverfish and “springbugs.” The mystery spider, it was assumed, fed on such ant guests – in the subterranean world of the ant colony.

The scientific journey expanded in 2014, when Martin Ramirez, an Argentinian expert on spider DNA, assembled a team to study the mystery spider. They found the spider’s lineage had diverged long, long ago – its closest relatives appear to be in Africa and Australia. The mystery spider, they concluded, represented a previously unknown spider family. They named the creature Myrmecicultor chihuahuensis – the “ant-worshipper” of the Chihuahuan Desert.

Discovering a new spider species isn’t uncommon – there are likely thousands unknown to science. But Horner, who began his career in the 60s, said finding an entirely new family is another matter.

“It’s very, very remarkable,” he said. “I would say that, since I’ve been in the business here in the United States, it’s maybe the third or fourth time.”

The research continued. In 2017, the spider was found at UT-El Paso’s Indio Mountains Research Station, in Hudspeth County. Horner and colleague Paula Cushing excavated ant nests at Dalquest, and found the spiders there.

It raises an obvious question: how does a spider make its home in an ant colony, without triggering the ire of the ants? Harvester-ant stings pack a punch. And the ants are much larger than the spider – an ant could easily dispatch the invader with a single snap of its mandibles.

The answer may lie in chemistry. Chemical signals called pheromones are a central means of ant communication. The spider may produce pheromones that mimic the ants’, providing it with a chemical camouflage.

To test it, Horner, Cushing and Jesse Rogers, a Midwestern chemistry professor, trapped both ants and Dalquest spiders – to collect pheromones for analysis. After their first attempt, they the left the ants and spiders together in the trap, while they took a dinner break. When they returned, all the ants were dead.

The scientists had applied a compound to the ants as part of the research. They suspected it might have been the cause of death.

They were back in the field the next day, and again held ants and spiders in a single trap.

“Except this time we watched to see what’s going on,” Horner said. “And those spiders killed those ants. They would come up behind them. They’d sneak up on them, jump in and bite that back leg. Then they would back off. It was crazy.”

The envenomated ant was dead in under a minute. The spider returned, carried off its heavy prey, and sucked out the innards.

And in a remarkable display of strength, the spider employed an unusual technique when other ants threatened to interrupt its meal.

“I couldn’t believe it because of the size of the things,” Horner said. “But those spiders could pick those ants up. And if another ant came by while he was feeding, they would throw up the body of the ant they were feeding on, and it served as a shield to other ants coming by. They were protecting themselves with the body of the ant they were feeding on.”

The scientists were stunned to see the ambush first-hand – it was scientific serendipity. It did, however, cast a shadow on the mystery spider’s scientific name.

“They named this as ‘ant worshipper,’” Horner said. “That is a very bad name. Because it doesn’t worship ants. It eats them.”

Research on the mystery spider is ongoing. Analysis suggests the spider does indeed produce pheromones that allow it to live amidst its prey, undetected.

The Dalquest spider is indicative a broader mystery – of the strange, often hidden life that thrives in this unforgiving land.

Nature Notes is supported by the Shield-Ayres Foundation and produced by Marfa Public Radio with the Sibley Nature Center. The program can be heard each Tuesday and Thursday, at 7:45 a.m. and 4:45 p.m., Central time, on KRTS Marfa, 93.5 FM, and KXWT Odessa/Midland, 91.3 FM. This episode was written by Andrew Stuart.


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