Impact of the Argentine ant, Linepithema humile on the native ants of Santa Cruz Island, California

We examined the impact of the non-indigenous Argentine ant, Linepithema hum ile (Mayr), on the native ants of Santa Cruz Island (SCI), the largest of t he California Channel Islands. Linepithema humile, a South American native, was first found on SCI in 1996 and now occupies two areas comprising less than 1% of the island. We surveyed ants using four methods: visual surveys, bait stations, tree surveys, and soil/litter samples. We found a total of 23 ant species, including two species not native to SCI: Cardiocondyla ecto pia Snelling and Linepithema humile. Numerous native ants occurred at sites uninfested by L. humile and co-occurred with L. humile at the outer bounda ries of L. humile-infested territory, but at sites more than 10 in within L . humile-infested territory, all but two of these species disappeared, prob ably due to exclusion by L. humile. Only two tiny ant species, Solenopsis m olesta Say and Monomorium ergatogyna Wheeler, were found to coexist deep wi thin the L. humile-occupied areas.