The invasive Argentine ant Linepithema humile (Hymenoptera: Formicidae) in Northern California reserves: from foraging behavior to local spread

We review the results from a 20-year study of the spread of the invasive Argentine ant, Linepithema humile (MAYR, 1868), in a reserve in Northern California. Ecological studies show that Argentine ants disrupt native ant communities. The best predictor of Argentine ant distribution is proximity to human disturbance, because buildings and irrigation provide water in the dry season and warm, dry refuges during the rainy season. Our studies of the effects of habitat and climatic factors suggest that human disturbance promotes spread, while lack of rainfall and interactions with native species, especially the native winter ant, Prenolepis imparis (SAY, 1836), slows spread in areas further from human disturbance. Genetic and behavioral studies indicate that seasonally polydomous colonies span 300 600 m in the summer when they are most dispersed, and contract to one or a few large nests in the winter. There is no evidence of mixing between nests of different colonies. Studies of foraging behavior show that searching behavior adjusts to local density, that arriving first at a food resource provides an advantage over native species, and that recruitment to food occurs from nearby existing trails rather than from more distant nests. We continue to monitor the spread and impact of the Argentine ant at Jasper Ridge Biological Preserve in collaboration with citizen scientists. We are investigating how Argentine ants modify and expand their trail networks, the interactions that allow the winter ant to displace Argentine ants, and the role of human disturbance on the impact of Argentine and other invasive ants in native communities.