A New Symbiosis: Ants Observed "Cleaning" Larger Ants in Arizona

A previously undocumented cleaning interaction between two ant species has been documented by an entomologist in southeastern Arizona. The behavior, observed between larger harvester ants and smaller cone ants, is described as the first known example of one ant species cleaning another, much larger ant species.

The Observation

The interaction was observed and documented by Mark Moffett, a research associate at the Smithsonian's National Museum of Natural History, during a visit to a research station in Arizona's Chiricahua Mountains. The findings were published in the journal Ecology and Evolution.

Observed Species:

• Harvester Ants: Pogonomyrmex barbatus
• Cone Ants: An undescribed species within the genus Dorymyrmex

Documented Behavior:

• A harvester ant would approach a cone ant nest and stand motionless with its mandibles open.
• Within approximately one minute, one or more cone ants would emerge and climb onto the harvester ant.
• The cone ants used their mouthparts to lick the body surfaces of the harvester ant, including between its open jaws.
• The harvester ants tolerated this behavior without biting or showing aggression toward the smaller ants.
• Interactions lasted from under 15 seconds to over five minutes, with up to five cone ants participating simultaneously.
• To end an interaction, the harvester ant would buck or dislodge the cone ants, sometimes falling onto its back before departing.
• Moffett documented at least 90 such interactions over several days of observation.

This behavior represents the first known example of an ant species cleaning a much larger ant species.

Scientific Context and Analysis

Moffett compared the interaction to marine cleaning symbioses, where smaller fish or shrimp clean parasites and dead skin from larger fish.

Key observations that distinguish the behavior include:

• Cone ants only performed cleaning on living harvester ants. They showed no interest in frozen harvester ant specimens placed near their nests.
• The harvester ants appeared to initiate the interaction by approaching the cone ant nests and assuming a stationary, open-mandibled posture.

Potential Benefits and Unanswered Questions

The specific benefits for each species have not been established. Moffett has proposed several hypotheses for further investigation:

Potential Benefits for Cone Ants:

• The cone ants may consume material they remove from the harvester ants' bodies. Moffett suggested this could include calorie-rich particles, such as flakes from seeds the harvester ants eat.

Potential Benefits for Harvester Ants:

• The cleaning may remove parasites, fungal spores, or debris from body areas that are difficult for the harvester ants' own nestmates to reach.

Moffett noted that future research is needed to determine if the cleaning behavior reduces infections in harvester ants or affects the microbiome of either species.

Research Background

Mark Moffett specializes in studying the social biology of ants and other animals. The cone ant species involved in the cleaning behavior has not been formally described by science. All ants observed participating in the interactions were worker ants, which are female.