When it seems there is nothing new under the sun, something new has been found in the bright glare of West Texas' Chihuahuan Desert. Twenty years after its discovery at Midwestern State University's Dalquest Desert Research Station (DDRS), near the Big Bend area, a new family of spiders has officially been recognized by the world's taxonomists, increasing the number of spider families to 120.

"The bottom line is this is a big deal in the world of spiders. Finding a spider that can't be identified is rare," said Dr. Norman Horner, Professor Emeritus of Biology and former Director of Natural Laboratories at MSU Texas. The "Texas Mystery Spider," as it was called for 15 years, puzzled nine world-renowned spider taxonomists.

Horner had a highlight-filled career of nearly 40 years at MSU Texas, including being named Hardin Professor in 1976, receiving the Faculty Award in 1983, and serving as Dean of the College of Science, Mathematics & Engineering from 1999 until his retirement in 2006. Because of his special interest in spiders, he was part of a worldwide group of scientists. "Studying spiders allowed me to meet and become friends with fellow araneologists across the U.S. and other parts of the world," Horner said. He would need to call on that network of spider specialists to help with a unique discovery, one that led to what he considers the high point of his career.

In 1999, Greg Broussard, one of Horner's graduate students, found an unknown specimen of spider in pitfall traps as he was conducting a spider survey on the DDRS. From there, the mystery spider went up a chain of hierarchy in the zoology world. Horner sent the spider to James Cokendolpher, former assistant curator and research scientist at Texas Tech University (an MSU alumnus and former student of Horner's), who sent the spider to Darrell Ubick, spider taxonomist at the California Academy of Science, who sent the mystery spider to the world's leading spider taxonomist, Dr. Norman Platnick at the American Museum of Natural History in New York.

Platnick emailed Horner with questions about the spider then organized a group of taxonomists to search the DDRS for more. The trip resulted in a single specimen caught in a trap Horner had set one month before the trip.

Since Broussard's initial find, the spider has been found in other areas in the Chihuahuan Desert. In 2008, while the spider was making the rounds in search of an identity, Dr. David Lightfoot from the Museum of Southwestern Biology at the University of New Mexico found a specimen on top of harvester ant beds approximately 208 miles south of the DDRS in Cuatro CiÚnegas, Mexico.

He carried specimens back to UNM, where he gave them to his museum's former senior collection manager, Dr. Sandra Brantley, for identification. "She had no idea what they were and sent them to Platnick," Horner said. Platnick told Brantley that this was the same spider Horner had been working on. Horner and Lightfoot exchanged information, with Lightfoot making the association with the harvester ants.

"I began setting traps close to ant nests and started catching many more. To date we have taken 140 specimens from the DDRS," Horner said.

Platnick retired in 2014 and turned the project over to Dr. Martin RamÝrez, who was Platnick's postdoctoral student, before his retirement. RamÝrez worked at the Museo Argentino de Ciencias Naturales in Buenos Aires, Argentina, and is one of the world's leading authorities on spider DNA analysis.

RamÝrez led an international team of 10 scientists as they analyzed the mystery spider's morphology and six mitochondrial and nuclear DNA markers to unravel the evolutionary affinities of the species, which turned out to be the sole representative of an entirely new lineage. They described the species in detail and named it Myrmecicultor chihuahuensis.

The spider is associated with at least three species of harvester ants, Pogonomyrmex rugosus, Novomessor cockerelli, and N. albisetosis, which is the reason for its name: "myrmex" is the ancient Greek word for ant, and "cultor" is Latin for worshiper, follower.

"The ant nests are very peculiar places to live: dark, with special environmental conditions, and very demanding on avoiding or cheating the nest's owners," RamÝrez said. "Many spiders adapted to live with ants have accumulated morphological modifications in evolution, to a point when it is very difficult to tell their relationships by their morphology. Myrmecicultor is one of these cases, hence the DNA sequences were essential to uncover their ancestry."

In 2015, Horner contacted Dr. Paula Cushing from the Denver Museum of Nature and Science. She has spent much of her career working with spider and ant relationships. Cushing excavated entire nests of N. albisetosis ants on the DDRS, and found the spiders living in ant chambers. What they eat in there is a mystery, but because of their small size they likely prey on other insects living with the ants.

In 2017, Horner asked Dr. Jerry Johnson, Director of Indio Mountains Research Station in Hudspeth County, Texas, which is owned and operated by the University of Texas at El Paso, if he could hunt for the spider there. Horner found three more mature males associated with ants.

In the spring and summer of 2018, Ubick, Cushing, and Horner began preparing the manuscript for publication. RamÝrez and Dr. Christian Grismado of the Museo Argentino de Ciencias Naturales analyzed the morphology and made comparisons with other spider groups' DNA. The spider is not closely related to any other known family. The article, "Myrmecicultoridae, a New Family of Myrmecophilic Spiders from Chihuahuan Desert," was published June 26 in "American Museum Novitates," No. 3930, with author credits to RamÝrez, Grismado, Horner, Ubick, Platnick, Cushing, and other colleagues.

"The description of this new family opens up many new avenues for future research, from attempting to better identify the closest relatives of these spiders, as well as studying the intricate relationships between the spiders and the ants they live with," Platnick said. According to Platnick, new families have been recognized based on previously unknown species only seven times in the last 88 years - in 2012, 1980, two families in 1955, 1947, 1940, and 1931.

"There are many more things we need to find out, such as what they're really eating and why they're living with three different kinds of ants," Horner said.

What is known about the spiders is that they appear to only come to the surface after a rain event, probably when the ants they cohabitate with have a reproductive swarm. In addition to not being closely related to any other family of spiders, it has ancient origins. It has a range in the Chihuahuan Desert of about 350 miles from Coahuila, Mexico, to Hudspeth, Presidio, and Brewster counties of the Big Bend region of West Texas.

For the scientists involved, finding Myrmecicultor's place in the taxonomic world has been a lesson of patience and cooperation. "This study was made by scientists with different expertise, in ecology, morphology and evolution," RamÝrez said. "I think it is an example of the importance of international collaboration for studies in taxonomy and evolution."

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