Three species of bristletails (Thysanura: Nicoletiidae), Trichatclura manni (Caudell), T. borgmeieri Silvestri, and Grassiella rettenmeyeri Wygodzinsky, were found living with army ants (Formicidae: Dorylinae) in Panama. Each species has been found with about six species of army ants. These Thysanura live within the ant nests and rarely are seen in diurnal raid columns. When the ants emigrate, the thysanurans run in the columns or ride on large larvae or booty carried by the ants. All specimens kept in laboratory nests died or were killed by the ants within a few days. Usually the ants seem to ignore the Thysanura which climb all over them. Because most immature specimens were found at the beginning of the nomadic phase of the ants, it is thought that the life cycle of T. manni may be synchronized with that of the host. T. manni licks and scrapes the surface of the ants and also feeds on fluids oozing from booty. T. manni runs rapidly on the tips of its tarsi with its long antennae and maxillary palpi extended in front and its abdominal styli held vertically. The Thysanura are able to follow the chemical trails of the ants. Except for the small amount of booty which they eat, they do not appear to be detrimental to the ants and may help keep their bodies and nests clean.