Honeydew harvest in the western thatching ant (Hymenoptera: Formicidae)

Abstract

Honeydew is a critical resource for colonies of the western thatching ant (Formica obscuripes Forel) living in shrub-steppe habitat of the Great Basin Desert. Workers of this ant collect and deliver honeydew to their primary nest in a highly organized way. Honeydew collectors (tenders) show complete fidelity to a single plant and to a distinct group of aphids throughout their foraging lives. At night and during the heat of the day, tenders split their time between tending and making frequent trips to a secondary nest at the plant base, where they transfer some of their honeydew to larger workers (transporters) for ultimate transport back to the primary nest. Both tenders and transporters deliver honeydew at least twice per day along well-established trunk trails, once in the morning and once in the late afternoon, when it is both cool and light. This same foraging pattern occurs each warm day as the summer progresses, with the identity of tenders gradually changing as old workers are replaced by new workers formerly engaged in duties in the interior or on the surface of the primary nest. This highly organized harvesting system underscores the importance of honeydew for nutrition and for territorial defense in the western thatching ant.