A tiny ant that uses pine mycorrhizal fungus to line its nest

Colonies of the tiny ant, Pheidole adrianoi line the chambers of their nests with whole or fragmented black sclerotia (resting stages) of an ectomycorrhizal fungus associated with longleaf pine. Mycelia sprout abundantly from the fragments, binding the surrounding sand into stable structures. The number of whole sclerotia in nests ranged from 480 to 9400, but the accumulated fragments probably bring the total much higher. The behavior represents a large investment in foraging and fragmentation. Tests that the ants eat sclerotia or mycelia were negative, as were tests of antibiotic activity against soil bacteria and fungi. Zinc casts of nests showed them to be 25 to 70 cm deep with three to seven chambers connected by a thin, vertical shaft. Excavation and census of live nests averaged 40 cm deep, with 70 minor workers and 13 major workers. Most nests were queenless even when they contained brood, suggesting that colonies were polydomous, a condition confirmed by occasional trails between nests. Portions of the chambers of live nests served as trash piles in which broken sclerotia, former repasts and dead workers accumulated.