These beetles are crepuscular (active primarily at twilight). The adult males are seen on the wing from May to August where they actively fly about looking for females, especially on warm summer evenings, where they will fly to light.
Adults usually only live for a few weeks; their sole adult existence is to mate.
Adult stag beetles are not known to feed. However, they do drink sweet fluids such as decomposing fruit and tree sap.
During the breeding season, the male stag beetles use their magnificent mandibles as a warning signal to other males, raising them in a defensive and aggressive posture to fight off a contender. They are skilful wrestlers and can even stand up on their hind legs to throw an opponent.
Their mandibles or mouthparts are sometimes referred to as ‘antlers’ as they resemble and are employed in much the same manner as a deer’s antlers might be, and from which the stag beetle gets its name.
Courtship involves the male circling the female with his impressive antlers raised and wide open. So strong is the mating instinct that males are known to attempt to mate with dead females and as many as four males may attempt to mate with just one female. Once mated the female finds a dead wood habitat to lay her eggs, after which she dies.