Stag Beetles are only active in the summer months. Having spent up to 6 years underground in their larval and pupal stages, the fully formed “adult” beetles start to emerge any time from around May and only live for about 3 months. During this time the beetles will mate, and females will lay eggs, starting the life cycle all over again.
Whilst some individuals may survive a bit longer than others, none of them will live through another winter – if you accidentally come across a Stag Beetle living underground during the winter months, it will be one that has pupated during the autumn and is waiting to emerge the following summer, rather than one that is hibernating for the winter.