Adult male stag beetles emerge in May or June, depending on the weather, followed shortly after by the females. The male has strong wings underneath the wing cases (elytra) and he flies at dusk in search of females. The flight can be rather erratic and the beetle sometimes flies indoors through open windows or doors, attracted by the light - and sometimes he bumps into things and crash lands.
When the male has found a female, he lifts his head, opens his antlers wide and walks around her, showing himself off. If two males are interested in the same female, they will fight each other, using their antlers like a male deer. The stronger of the two turns the other onto his back and the loser retreats. Injuries are rare as the encounter is more of a display of aggression than a dangerous fight.
After mating, the female finds some moist decaying wood in which to lay her eggs. She prefers oak woodlands but where these are scarce she will seek out logs and old tree stumps in parks, gardens and hedgerows. When she has laid her eggs, she dies, and the male does not last much longer.
Each egg hatches into a creamy coloured larva, looking like a fat, wrinkly grub with an orangey-brown head and six stubby legs. It has tough jaws for tearing up and chewing decaying wood. This type of food is not very nourishing, so it takes three to five years before the larva is ready to turn into a pupa. The adult beetle develops inside this pupal case, which remains hidden inside a decaying tree stump all through the winter. The fully-formed adult beetle will not emerge until the weather becomes warmer in May or June of the following year. The cycle then starts over again, as the males fly off in search of a mate. The flight season lasts only until August and by the time winter arrives, all the adult beetles have died.
Read More: Threats to the Stag Beetle