The tropical bont tick, Amblyomma variegatum, is an African tick species which infests livestock and wildlife. It was probably introduced in the central eastern islands of the Caribbean during the 18th or 19th century, with cattle shipped from Senegal. In Africa and the Caribbean, this tick is a vector of heartwater (a rickettsial disease of ruminants) and is associated with acute dermatophilosis (a bacterial skin disease of animals). Until 1948, only Guadeloupe and the neighbouring islands of Marie Galante and Antigua were infested with this tick species. Following increased agricultural commerce between Guadeloupe and Martinique, the latter became infested in 1948. Between 1967 (when the tick was identified in St Croix) and 1988 (when a male tick was reported in St Vincent), fourteen new islands were reached by this tick. Most of the dissemination of the tick to new islands cannot be explained by legal or illegal movements of livestock. Recently-determined circumstantial evidence strongly links the increase in populations of the cattle egret (Bubulcus ibis), a migrating bird established in the Caribbean circa 1960, with increased colonisation of new islands by A. variegatum. Considering the wide range of areas currently occupied by this bird species in the Greater Antilles and on the American mainland, there is a high probability that the tick will also expand its range and invade new areas. Eradication of A. variegatum from the Caribbean and thus from the western hemisphere, and the strengthening of measures to prevent inter-island movements of livestock, would be the only effective means of preventing this threat.