Effect of Weather on Infestation of Buildings by the Invasive Argentine Ant, Linepithema humile (Hymenoptera: Formicidae)

Abstract Weekly reports of the abundance of the Argentine ant, Linepithema humile, in 69 households for 18 mo (1/98–7/99) in the San Francisco Bay Area in northern California were compared with weather data. Ant abundance inside homes was highest in cold rainy weather, and there was a second smaller peak of ant abundance in hot dry weather. Pesticide use in the home decreased ant abundance, from one week to the next, only when ant abundance was extremely high.