Allonemobius fasciatus and A. socius have no identifying morphological features nor can males be distinguished by their calling songs. The two species were originally distinguished by allozyme assay (Howard 1983) and, in those areas where both species occur, allozyme assay remains the only way to tell them apart. However, studies in the eastern states have shown that A. fasciatus and A. socius are northern and southern species respectively, which overlap in their distributions narrowly in Illinois and New Jersey and broadly in West Virginia (Howard & Waring 1991).
In the eastern United States, three green bars indicate its southward limits along the three north-south transects studied by Howard & Waring (1991). The approximate northern limits of A. socius are indicated by a dotted red line. In the shaded area north of the dotted red line, the dots show county records of A. fasciatus (because A. socius does not occur so far north). South of the red line, the dots represent either A. fasciatus or A. socius. Farther west only A. fasciatus is known for certain with the exception of two records of A. socius from northern California (Weibel & Howard 2000a). The Texas record with a ? could be either A. fasciatus or A. socius.
