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By Root 633 0

a small hole—the nest entrance of a smaller, innocuous-looking cone ant, a species of Dorymyrmex. Within a few seconds, one of the cone ant workers dashed up onto the larger ant’s body. Using my camera as a microscope, I watched, my heartbeat audible in my ears, as the cone ant climbed all over the harvester, licking here and there. At one point she scrubbed between the harvester ant’s open jaws, like a fawn sticking her head in a lion’s mouth. After about thirty seconds of this attention, the harvester ant flicked the cone ant off with a brush of a foreleg and lumbered back to her own nest. A few minutes later another harvester ant came to the same area and was given a similar treatment. What ecstasy to see such a novel, and apparently unrecorded, behavior!

I had been visiting the biologist Howard Topoff to learn about the slavery ants around Portal, Arizona, when I came upon this instance of one ant species cleaning another in the desert flats below town. The cone ants’ boldness reminded me of the cleaner fish that nibble at the mouth and body of a larger fish that has stationed itself in a similarly rigid, open-mouthed posture, which encourages a cleaner to come aboard. As occurs among the fish, after a while the harvester ant tired of the attention or became irritated if her cleaner got carried away and gave her a nip. Sometimes too many—two or three—cone ants joined the first, at which point the harvester rolled on the ground to remove the cleaners before departing. However, when no cone ant came along, an ignored harvester ant sometimes backed into the cone ants’ nest entrance, virtually begging for attention.

From their earliest evolution, ants have needed to control the microbes that find sanctuary on their bodies and in the stagnant, moist depths where most species nest. Group living in such places is a public-health challenge, requiring the rapid removal of the dead, among other essential tasks. The metapleural glands on the thoraxes of ants have been one of their primary weapons in germ warfare. Like humans scrubbing down with soap, workers use their legs to transfer antibiotics from the metapleural glands to other parts of their anatomy, spending as much time primping and grooming as the average supermodel. They are equally fastidious with each other, licking their sisters’ hard-to-reach spots and spreading pharmacological secretions throughout their living spaces whenever an infection shows up.14

Workers of Dorymyrmex near Portal, Arizona, climbing on a larger harvester ant,Pogonomyrmex maricopa, to lick her body. In this image, the harvester ant has begun to kick them away.

Why do harvester ants invite interspecific cleaning by cone ants, when harvester ants, like other species, can groom one another? Perhaps cone ants offer a special brand of antibiotic, or perhaps, being small, they reach spots that other harvester ants miss. Harvester ants are flecked with sugary flakes from the seeds they eat, which might make them prone to bacterial infection. The cone ants must get a reward, perhaps nourishment from such sweet substances.15

For leafcutters, issues of hygiene and nutrition extend beyond ordinary concerns of body and nest to the needs of the gardens. As with any growth medium, the leaf mulch becomes exhausted of nutrients by the produce growing on it. In ant gardens, this takes a few weeks. The hyphae then retreat, leaving behind nutritionally barren remnants filled with a concentration of the plant toxins rejected by the fungus. The inability of the fungus to break down cellulose means the gardens generate mountains of such trash, as I had seen in the colony excavation in Botucatu, Brazil. One Atta sexdens colony contained 475 kilograms (half a ton) of refuse in 296 underground chambers, while the nest of another species had a similar amount of waste in a single huge chamber.16

If the old substrate and foreign matter aren’t removed promptly, they begin to spoil. Sanitizing goes into high gear when the policing minor ants discover an infected spot. The minors take contagion spores into the same