Workers of this species look superficially like the common black garden ant Lasius niger, but can be distinguished in the field by their behaviour when disturbed. On warm days the small black workers (2.6-4.2 mm) dart around very quickly and aggressively with their gasters slightly raised. Under magnification they completely lack the standing body and appendage hairs of L. niger, the petiole node is also inconspicuous and overhung by the first gastral segment also workers and gynes lack a conical hair-fringed acidopore at the tip of the gaster (instead there is a simple lateral slit).
Tapinoma erraticum has been shown to have two species present within it, T. erraticum and T. subboreale. The two species are very difficult to separate, relying on characters such as depth of the clypeal notch and shape of the male genitalia. To make things more confused T. subboreale was originally mis-identified as T. ambiguum or T. maderiense! Records of T. ambiguum or T. maderiense will therefore direct to T. subboreale. Any records of ‘T. erraticum’ which have not been re-examined in the light of Seifert 2012 should be placed in T. erraticum agg.
Little is known about any differences in the biology, ecology and distribution of each species and this would merit further investigation.
T. erraticum is confined to the southern counties of England and the Channel Isles, largely following the distribution of lowland sandy heaths but with a few records from other inland and coastal sites. Nests are easily overlooked and often only isolated colonies are found.
The map shows records for T. erraticum agg. and may include some records for T. subboreale.