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| The Atta roach in a fungus garden. (Photo: Alex Wild) |
A moonless springtime night at Brackenridge Field Lab. The sun will rise shortly. The Texas leaf-cutter ants (Atta texana) have started their nuptial flights as the winged virgin females and much smaller males fly about. Some of the queens are not alone in their journeys however. Unbeknownst to them, cockroaches are attached to their backs.
Whatever in the world is a cockroach doing on the back of an ant? Turns out, quite a lot that has been of interest to a graduate student in the Department of Integrative Biology.
Meet Zach Phillips. He studies organisms that live with leaf-cutter ants. Zach believes his uncommon life choice came about through his love of strange organisms, student housing co-ops (another type of “colony” often inhabited by roaches), and of Archy and Mehitabel, characters created in 1916 by humorist and columnist, Don Marquis, for the Evening Sun Newspaper. As you might guess, one of these characters is a roach.
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| "Archy." (Public Domain, https://commons.wikimedia.org/w/index.php?curid=18353670) |
Now meet the object of Zach’s research: the “Atta” cockroach, Attaphila fungicola. These roaches are myrmecophiles (“ant loving” organisms), and are specifically dependent on leaf-cutter ant colonies for their survival and reproduction. Entomologist William Morton Wheeler (1865 – 1937) had a more colorful term for the relationship between Attaphila and its leaf-cutter ant host: “myrmecoclepsy, or thieving.” He first observed these roaches in 1900, most likely while teaching here at UT, during a time when leaf-cutter ants could be observed traipsing across Congress avenue.
The process is like this: The leaf-cutter ants forage for and return to their nests with plant material, and through a series of steps carried out by different sized workers, convert this plant material into a fungus that feeds the colony. The thieving roach eats the fungus, too. “So, if we imagine the ants and their fungal garden as a colonial version of Mr. McGregor and his vegetable garden,” Zach elaborates, “the roaches are Peter Rabbit.”
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| Zach hard at work. (Photo: Jessica Lee) |
Wheeler observed that these roaches are often invisible to their hardworking hosts, likely due to the roaches’ mimicry of the ants’ chemical profile. Ants do not “see” the way people do. What they lack in vision they make up for in their sense of smell. Ants have a remarkably sophisticated sense of smell which allows them to pick up odors that in turn dictate their behavior and social organization. The Atta roach capitalizes on this by mimicking the odor of the leaf cutter ants, but this mimicry may be imperfect, and the roaches still seem to regularly be recognized by some of the ants as intruders. This could explain one of Wheeler’s other interesting observations about the roaches. He noticed that the Attaphila he collected all had incomplete antennae, possibly having been clipped off by ants continually tending the fungal garden, or possibly by ants actively attacking the roaches. In addition to their chemical mimicry,” Zach says, “the roaches, like Peter Rabbit, are especially good at running through and hiding in the garden.”
The Atta roach may have it made in the shade, literally, as it can spend its entire life inside the ant colony. Some leave only when the virgin leaf-cutter queens are ready to depart home for good and mate mid-air with male ants from other colonies. The wingless roaches ride the virgin queens during their mating flights, which has led to the assumption that after flights the roaches remain with queens beginning new colonies. However, early in his PhD work, Zach observed that new leaf-cutter queens (termed “foundresses”) and roaches don’t get along in the lab, which led him to test other possible modes of roach “between-colony transmission.” He’s just finished this spring’s field season at Brackenridge Field Lab.
The Brackenridge Field Lab is a crucial hub for Zach’s research, with the proximity to campus, ease of getting there, and leaf-cutter colonies in abundance. It also helps with his nocturnal hours doing field work that a 24 hour diner is just a few blocks away. “[BFL] is like having my own ecology beat, which has given me the opportunity to become familiar with the ants and their habitat in a way that can’t be replicated in a lab or at a distant research station,” he says. “It also doesn’t hurt that BFL is crawling, and they do crawl, with world-class ant biologists who are generous with their time and expertise, and is regularly visited by great undergrads that help me with research.”
Zach notes that this tiny roach lacks a common name, but is happy to suggest one. “The Khaleesi roach,” he says, noting that the fictional heroine from Game of Thrones also takes a ride on the back of a much larger flying creature. In this case, a dragon. However cool riding one must be, Zach still feels leaf-cutter queens are much cooler. “While a single dragon can destroy a city, a single leaf-cutter queen can give birth to a city,” he says. “In general, insects are more impressive than imaginary creatures.”
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| Queen leaf-cutter ant and her smaller daughter workers. (Photo: Alex Wild) |
SOURCES
Gilbert, Larry (Professor, Dept. of Integrative Biology)
Phillips, Zack; Zhang, M.M.; Mueller, U.G. “Dispersal of Attaphila fungicola, a symbiotic cockroach of leaf-cutter ants”. Insectes Sociaux. December, 2016.
Wheeler, William Morton. "A New Myrmecophile from the Mushroom Gardens of the Texan Leaf-Cutting Ant". The American Naturalist. November, 1900. 34 (407): 851–862.
“Texas Leaf Cutting Ant, Atta texana” Urban and Structural Entomology Program at Texas A&M University (accessed online: https://urbanentomology.tamu.edu/urban-pests/ants/leaf_cutting/)
