Tetramorium lanuginosum is a small ant with a reddish head, mesosoma and waist contrasting with a dark gaster, and a dense pelt of long white pilosity. This species has a monomorphic worker caste with 12-segmented antennae, three-segmented antennal club, antennal scrobes, short antennal scapes that do not surpass the posterior margin of the head, a gradually sloped mesosoma, and strong propodeal spines. Like all myrmicines, T. lanuginosum has two waist segments and a gaster armed with a stinger. Tetramorium lanuginosum (formerly known as Trigliphothrix striatidens) is widely distributed across the Pacific and other tropical regions. It is most often encountered in forest leaf litter. The species is not known to cause significant damage to ecological or agricultural systems.
Diagnosis of worker among Antkey species. Worker caste monomorphic. Head shape roughly subrectangular. Antenna 12-segmented. Antennal club 3-segmented. Antennal scapes not conspicuously short; easily extended beyond eye level; do not extend beyond posterior margin of head. Antennal scrobe present. Antennal insertion surrounded by a raised sharp-edged ridge. Posterolateral corners of head unarmed, without spines. Eyes medium to large (greater than 5 facets); distinctly less than half head length. Frontal lobes do not obscure face outline between mandible and eye; relatively far apart so that the posteromedian portion of the clypeus, where it projects between the frontal lobes, is much broader than one of the lobes. Anterior margin of clypeus notched. Mandibles triangular. Cephalic dorsum with short lateral rugae intersecting longer longitudinal rugae. Mesosoma with erect hairs. Pronotal spines absent. Propodeum armed with long robust spines. Slope of mesosoma gradual. Waist 2-segmented. Petiole with an evenly rounded node; pedunculate; lacking large subpetiolar process postpetiole attached to lower surface of gaster. Postpetiole not swollen; in dorsal view not distinctly broader than long or distinctly wider than petiole. Long, thin erect hairs very abundant and forming a thick pelt; at least some of them bifid. Color uniformly dark brown to black.
Tetramorium lanuginosum is distinguished from its fellow congeners that are introduced in the United States by the following combination of characters: (1) petiolar node evenly rounded (versus square-shaped for T. bicarinatum, T. nr. caespitum, T. caldarium, T. simillimum and T. tsushimae; versus wave-shaped for T. insolens and T. pacificum); (2) erect hairs long, thin, densely distributed and at least some bifid (versus short, thick and sparse for T. caldarium and T. simillimum; versus moderately abundant but none bifid T. bicarinatum, T. nr. caespitum, T. insolens, T. pacificum, T. tonganum and T. tsushimae); (3) cephalic dorsum with short lateral rugae intersecting longer longitudinal rugae (versus primarily subparallel, non-intersecting longitudinal rugae for T. nr. caespitum and T. tsushimae); and (4) propodeal spines long and robust (versus small triangular teeth in T. nr. caespitum, T. tsushimae, T. caldarium and T. simillimum).