Length: 15-25 mm
Dorcus parallelus is dark brown to almost black, perhaps with a purple cast as shown. The mandibles of the male are not as huge as they are on certain other Stag Beetles, but they are interesting for having a single "horn" on each mandible. The lucky naturalist may find an adult wandering around on the ground, but more often they are noticed when they show up at lights. Adults are most commonly encountered in May, June, and July. The larvae feed in decaying stumps and roots of hardwoods including Oak, Linden, Maple, and Elm.
One text mentions that females are "rare" and certainly it seems they are encountered less often than are the males. The appearance of females is similar to that of the males, with the head and mandibles a little smaller.
Left: Lateral view of Dorcus parallelus
At right, a close-up view of the male's head and pincers. Note the horn on each pincer, most easily seen on the beetle's left horn in this photo.