The coconut mite, Aceria guerreronis Keifer, was collected for the first time in Puerto Rico in 1977. It was reported for the first time in Florida in 1984, although it may have been present in the state since the 1950s. On the basis of damage symptoms observed during 1986-87, the coconut mite was distributed in almost all plantings of coconut in Puerto Rico. The percentage of trees with symptoms was highest on the west coast, where planting density is highest. During the same period, the percentage of coconut palms infested with coconut mites varied from 66 to 98% at different sites on the Florida Keys. On the Florida mainland, the percentage of trees with coconut mite damage was usually less than 7%. At several sites on the Florida mainland revisited in 1988, coconut mites had spread locally. At Playa Tres Hermanos in Añasco, Puerto Rico, and Bahía Honda Key, Florida, where monthly sampling was conducted, coconut mite population fluctuations did not appear to be strongly associated with dry and wet periods or mean daily temperatures. A list of mite species associated with the coconut mite was reported. It included four species reported for the first time in Puerto Rico. In Puerto Rico, Bdella distincta preyed on both coconut mite and Steneotarsonemus furcatus. In Florida, Amblyseius largoensis, Neoseiulos mumai, and N. paspalivorus were observed preying on coconut mites. However, these predators apparently do not significantly affect coconut mite populations. Tarsonemus sp. inflicted damage on the coconut similar to that caused by the coconut mite. Coconut mites beneath tepals of coconuts exposed to —1.5° C for 5.5 hours were not affected adversely by this treatment. Some eggs remained viable after exposure to —3° C up to 5 hours. Coconut mites survived at 5° C for 10 days. Thus, coconut mites are capable of surviving most winters on the Florida mainland.