Length of Northern Spreadwing: 32-42 mm
Length of Southern Spreadwing: 36-46 mm
Until recently Lestes australis had only subspecies rank, as Lestes disjunctus australis.
Both of these two similar species are found in West Virginia, about equally common, with a statewide rank of S2S3. They are quite similar and may be difficult to tell apart. Two of the best ways to separate them are size, and flight season. Small individuals (32-35 mm) may be assumed to be Lestes disjunctus, while large individuals (43-46 mm) may be assumed to be Lestes australis. Individuals seen in April, May, or early June may be assumed to be Lestes australis, as may individuals flying in October or early November.
Of course, these two methods of identification have serious limitations. Individuals of moderate length (36-42 mm) could be either species, and individuals that fly from late June through September could also be either species.
Examination of the ovipositor, or
the male's cerci, can further aid the identification, but these
examinations are tricky as the differences can be subtle. To make
matters worse, another species (rare in West Virginia), Sweetflag
Spreadwing, is also very similar. Ed Lam (2004) advises, "For
this difficult group, tandem pairs should be studied, as one sex
reinforces the identity of the other."