Abstract: The longhorn crazy ant, Paratrechina longicornis (Latreille, 1802), is a ubiquitous agricultural and household pestthroughout much of the tropics and subtropics and a pervasive indoor pest in temperate areas. I compiled specimen records of P. longicornis from > 2100 sites worldwide and analyzed historical, ecological, and evolutionary informationto evaluate its known distribution, geographic origin, and potential future spread. I documented the earliest known P.longicornis records for 181 geographic areas (countries, major islands, island groups, Us states, and Canadian provinces),including many for which I found no previously published records, e.g., Anguilla, Argentina, Austral Islands, Bahrain,British Indian Ocean Territory, Cayman Islands, Comoro Islands, Dominica, East Timor, El Salvador, Gambia, Ghana,Gibraltar, Guatemala, Iles Eparses, Kenya, Maldives, Mali, Montserrat, Nepal, Nevis, Pakistan, St. Kitts, St. Lucia, Turksand Caicos Islands, Tuvalu, Maryland, Missouri, and Virginia. Paratrechina longicornis is arguably the most broadlydispersed of all ant species, distributed widely across the Old World and New World in both the northern and southernhemispheres. The successful worldwide spread of P. longicornis relates to its ability to flourish in highly disturbed andartificial environments, including ships at sea. Whereas P. longicornis records are most frequent near major commercialwaterways, I expect that with the increasing importance of air transport, P. longicornis will spread to more inland areasas well. Many P. longicornis records, including most if not all records from temperate latitudes, come from inside or nearbuildings. Because P. longicornis can live indoors anywhere that humans live, there is no limit to the latitude where itcould thrive. The worldwide distribution records of P. longicornis and two species-specific symbionts provide ambiguousclues to the original native range of P. longicornis. However, the distributions of three closely related Paratrechina species offer good evidence that P. longicornis is native to Southeast Asia and Melanesia.