Dolichoderus thoracicus is a brown to blackish brown species most easily recognized by the deep and broad concavity on the mesosomal dorsum separating the propodeum from the mesonotum, the strongly convex propodeum which forms a blunt posteriorly projecting protrusion, and the strongly concave propodeal declivity. The type specimen of the species was collected by the great naturalist Alfred Wallace from Sulawesi. Dolichoderus thoracicus is native to Southeast Asia, where, despite its use as a biological control agent, little is known about its basic biology. The species is capable of nesting opportunistically both in leaf litter on the ground and arboreally between leaves and fronds (Way & Khoo, 1991). Maschwitz et al. (1991)reported an undetermined species assigned to the ‘D. thoracicus group’ as the first Dolichoderine known to produce silk nests.
It is possible that the native range of D. thoracicus has been expanded in parts of Asia by intentional introduction (McGlynn, 1999b). Although it has not been reported to have established outside of Asia, the species has been intercepted occasionally at US ports of entry, and several interceptions are recorded from New Zealand (Ward et al., 2006). Dolichoderus thoracicus is known to suppress populations of various pests of perennial crops in Southeast Asia, most notably cocoa and sapodilla (Cuc & Van Mele, 1999; Khoo & Ho, 1992). In one study farmers in Vietnam were reported to encourage the presence of these ants in their orchards by providing artificial nesting and food resources, and 25% fewer farmers sprayed insecticides than in orchards where D. thoracicus was absent (Van Mele & Cuc, 2001).
Diagnosis of worker among Antkey species. Antenna 12-segmented. Antennal scape length less than 1.5x head length. Eyes medium to large (greater than 6 facets); do not break outline of head. Antennal sockets and posterior clypeal margin separated by a distance less than the minimum width of antennal scape. Dorsum of mesosoma with deep and broad concavity; erect hairs present. Propodeum with distinct and posteriorly projecting protrusion. Waist 1-segmented. Petiole upright and not appearing flattened. Gaster armed with ventral slit. Color uniformly brown to blackish brown.
Dolichoderus thoracicus is a morphologically variable species (Emery, 1887e), as evidenced by the high number of subspecific names (Shattuck, 1994). Among commonly intercepted ants, D. thoracicus is recognizable by the deep and broad mesosomal depression, the unique shape of the propodeum, and the strongly concave propodeal declivity. It is most likely confused with Ochetellus glaber, but can be separated by the deeper and broader mesosomal depression and the presence of erect hairs on the mesosoma.
Ochetellus glaber
Native range (Shattuck, 1994). Southeast Asia: Borneo, Cambodia, India, Laos, Malaysia, Philippines, Singapore, Sulawesi, Vietnam.
Introduced range. Not yet established outside of its native range.