The Invasive Ant Fauna (Hymenoptera, Formicidae) of Laysan Island, Hawaiian Islands National Wildlife Refuge

Abstract

Ants are not native to any of the Hawaiian Islands and invasive ant impacts on Hawaiian ecosystems have been profound, so documentation of ant diversity is crucial to understanding and managing these alien species. Changes to the invasive ant fauna on Laysan Island, Northwest Hawaiian Islands, were documented in 2005, fifteen years after the previous (1990) survey of the island. Six species were found on the island, all previously recorded. The common tramp ant Monomorium pharaonis was found to have greatly expanded its range to become the dominant ant on Laysan. During the same period, the range of the previously dominant ant species, Tetramorium bicarinatum, greatly decreased and the species was limited to the dense vegetation areas around the island’s central lake. Tetramorium simillimum, possibly the most recent introduction to the island, and previously the second most widespread species, was not located in surveys and is possibly extirpated. An invasive ant species has apparently not become established on Laysan in almost 20 years suggesting current quarantine measures are a successful deterrent to colonization events.