The American Cockroach (Periplaneta americana)is the most common species of Periplaneta in the US:
The Australian Cockroach (Periplaneta australasiae) can be differentiated by the increased contrast on the colors on the pronotum ("hood") of the cockroach, and confirmed by the presence of white bands on the outsides of the wings:
The Smoky Brown Cockroach (Periplaneta fuliginosa) can be identified by a uniform dark color of the pronotum (i.e. no pattern at all):
The Brown Cockroach (Periplaneta brunnea) can be difficult to differentiate from the American Cockroach. The cerci are stout compared with the thin cerci of the American Cockroach.
Early Instar Nymphs:
American Cockroach nymphs are solid brown with minimal variation in the hue over their body, from very early instars through last nymphal instar:
Smoky Brown Cockroach nymphs have early instars that are black with the notable exception of white on the proximal and distal antennae, a band of white on the thorax, and two lateral white marks on the abdomen:
Australian Cockroach and Brown Cockroach nymphs have similar white areas on the antennae, throax and abdomen, but the contrast is less striking because their bodies are brown rather than black.
Late Instar Nymphs
These can be very difficult to separate, with the exception of Australian Cockroaches, which have developed the more contrasting colors seen in the adult cockroaches:
Variable patterns have been seen in late-instar Brown cockroaches:
If the late instar nymph is light brown without much variation in color, it is likely to be an American Cockroach:
In addition to the species already in the guide, the Japanese cockroach Periplaneta japonica was discovered in Manhattan, New York in 2013. It is cold tolerant and has the potential to spread in the wild.