Understanding associations between insects and their plant habitats is a critical aspect of terrestrial community ecology. Of particular importance are small island communities, which may display high diversity but which are vulnerable to drastic alteration of the ecosystem due to the effects of invasive species. This study characterized ant and plant biodiversity in karst and beach flat habitats on the Micronesian island of Guam. Ant and plant species abundance were estimated at two beach flat habitats and in a leached limestone karst habitat on Guam. Ant and plant specimens were identified using published and unpublished keys. Shannon’s Diversity Index was used to compare communities. The majority of plant species showed high site specificity while ant species were more widely dispersed across the two habitats.