Diagnosis among workers of introduced and commonly intercepted species.
Antenna 9-segmented. Antennal club indistinct. Antennal scapes surpassing the posterior margin of head by more than 1/5th their length. Eyes of moderate size (greater than 5 facets). Eye length approximately equal to or slightly greater than malar distance. Head with or without distinct ocelli. Antennal sockets and posterior clypeal margin separated by a distance less than the minimum width of antennal scape. Dorsum of mesosoma lacking a deep and broad concavity. Metanotal groove present. Pronotum and mesonotum with pairs of erect hairs. Propodeum and petiolar node both lacking a pair of short teeth. Propodeum lacking posteriorly projecting protrusion. Metapleuron with a distinct gland orifice. Waist 1-segmented (may be hidden by gaster). Petiolar node appearing flattened. Gaster armed with acidopore. Gaster (especially first segment) with sparse pilosity, giving it a shiny appearance. Color yellow to brown.
The taxonomy of Brachymyrmex is in considerable need of revision before many of the current species names can confidently be applied to specimens. Brachymyrmex heeri can be distinguished from most other introduced members of the genus by the following combination of characters: (1) sparse pubescence on the first gastral tergite, (2) antennal scapes exceeding posterior margin of head by at least 1/5 their length, (3) erect hairs on the pronotum and mesonotum, and (4) eye length equal to or greater than malar distance. More yellowish specimens of B. heeri can be separated from the brown species B. patagonicus, but greater taxonomic study is required in order to separate darker B. heeri specimens. Joe MacGown (2012) suggests that dark B. heeri can be separated from B. patagonicus by the formers lack of ocelli, but the presence/absence of ocelli may be an unreliable character (Christopher Wilson, pers. comm.).