Adult size varies between different areas of its distribution, for example beetles from Spain, Germany, and the Netherlands are larger than those from Belgium or the UK.

In Britain, female Lucanus cervus are often confused with both sexes of the lesser stag beetle (Dorcus parallelipipedus).

[7][8][9] They can be distinguished as lesser stag beetles are smaller, with a completely black exoskeleton, and a larger, squarer head.

[5] Lucanus cervus has been associated with a range of trees including those in the genera oak (Quercus), lime (Tilia), beech (Fagus), willow (Salix) and certain species in other genera including black poplar (Populus nigra), ash (Fraxinus excelsior), horse-chestnut (Aesculus hippocastanum), wild cherry (Prunus avium), and common walnut (Juglans regia).

Males use their large mandibles to fight with each other in competition for females, intending to throw their opponent off the log or branch they are on.

[20] The work of entomologist Charlie Morgan during the late 1970s discovered that the pupae of the stag beetle live in the soil for about 3 months, then emerge in summer to awkwardly fly off to mate.

[citation needed] Adults suck up the liquids of nectar, fallen fruit, and tree sap.

Stag beetles spend most of their life as larvae and can take from 3 to 7 years for them to pupate,[21] but the lifespan of the adults is only a few weeks.

[citation needed] In a primary ancient forest in northern Italy, stag beetle males were less elusive than females.

The combination of air temperature and humidity determined the optimal weather conditions for male flights.

[24] Natural predators of L. cervus in Britain include cats, foxes, badgers, carrion crows, magpies, woodpeckers, kestrels, and false black widows; these tend to strike at the most vulnerable stage in the beetle's life cycle, when adults are seeking to mate and lay eggs.

[15] In the case of magpies, they have been observed in the field as waiting for emergence on a single site, subsequently consuming the beetle's abdomen.

[1] Lucanus cervus is registered in the second appendix of the Habitats Directive of the European Union from 1992, which requires that member states set aside special areas of conservation.