Cyclargus ammon (Lucas) has been established on Big Pine Key, Florida since at least 1997. The species arrived from Cuba, possibly with the assistance of a meteorological event. It inhabits rockland pine forests in Florida and is known to utilize as hostplants Acacia pinetorum, Acacia famesiana and Caesalpinia pauciflora (Fabaceae). The habitat, abundance, nectar sources and life history are detailed. The decline of endemic Cyclargus thomasi bethunebakeri (Comstock & Huntington) is also discussed. Once locally common in South Florida, there were no verified records of this subspecies during the period of March 1992-October 1999. It is now known to occur at a single location in the lower Florida Keys. Loss of habitat through coastal development is the likely cause of this decline, perhaps exacerbated by other factors such as succession, tropical storms, and mosquito control. Surveys are required to determine the current status of C. t. bethunebakeri in Florida.
