Diagnosis of worker among Antkey species. Worker caste monomorphic. Antenna 12-segmented. Antennal club indistinct. Antennal scape length less than 1.5x head length. Eyes medium to large (greater than 6 facets); do not break outline of head. Dorsum of mesosoma with weakly impressed metanotal groove, but never with a deep and broad concavity; dull with dense overlapping pubescence. Propodeum and petiolar node both lacking a pair of short teeth. Propodeum lacking posteriorly projecting protrusion. Mesopleuron shiny, not dulled by dense pubescence (less than 25 hairs). Metapleuron with a distinct gland orifice. Waist 1-segmented (may be hidden by gaster). Petiole upright and not appearing flattened. Gaster armed with acidopore. Distinct constriction not visible between abdominal segments 3+4. Gaster (especially first segment) with dense pilosity, giving it a dull appearance. Hairs long thick and produced in pairs. Pubescence density uneven, becoming denser on dorsum, more sparse laterally on pronotum and mesopleuron. Body color dark brown to black with strongly contrasting pale white hind and middle coxae.
Among other introduced and commonly intercepted Nylanderia species, N. steinheili can be distinguished from N. flavipes, N. guatemalensis, N. vaga and N. vividula by the dense amount of pubescence on the dorsal surfaces of the promesonotum and first gastral segment. Of the two remaining species (N. bourbonica and N. fulva) that have similarly dense pubescence in these regions, N. steinheili is distinguished by the color of the coxae which are uniform with the rest of the legs and body (versus strongly contrasting white), and by the uneven density of the mesosomal pubescence, which is dense on dorsum and becomes sparser laterally on pronotum and mesopleuron (versus uniformly dense across the mesosoma).
Nylanderia bourbonica, Nylanderia fulva.