Tetramorium caldarium is a small reddish ant. 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 small propodeal spines. Like all myrmicines, T. caldarium has two waist segments and a gaster armed with a stinger. Tetramorium caldarium is believed to be native to Africa and is now widely distributed across the Pacific and other tropical regions. The effect this species has on native biodiversity is not well known.