European Stag Beetle (Lucanus cervus): Facts and Life Cycle

What does a stag beetle look like?

The stag beetle is a big, heavy-bodied beetle with a black head and thorax and glossy chestnut-brown to reddish-brown wing cases. Males carry enormous reddish-brown mandibles, or jaws, that branch at the tips like a deer’s antlers. These “antlers” give the beetle its common name and its scientific name: cervus is Latin for deer.

Females are smaller and lack the antlers. Their jaws are short, curved and sharp, and their wing cases are usually darker. In Britain, females are often confused with the lesser stag beetle (Dorcus parallelipipedus), which is smaller, entirely dull black and has a broader, squarer head.

Like all beetles, the stag beetle has hard front wings that protect a pair of large, folded flying wings. Its elbowed antennae end in a small comb-like club, a typical feature of stag beetles.

How big is a stag beetle?

Size varies a great deal, mainly with how well the larva fed. Males usually measure 35–75 mm (1.4–3 in) from the tip of the jaws to the end of the abdomen, and some reach more, especially in the south and east of the range. Females measure about 30–50 mm (1.2–2 in). Beetles from Spain, Germany and the Netherlands tend to be larger than those from Belgium or Britain.

Small “minor” males with short jaws are common. Their size was fixed as larvae: an adult beetle does not grow. Why some males end up with huge jaws and others with small ones is explained in why stag beetles have big jaws.

Habitat and range

The European stag beetle lives across much of Europe, from northern Spain and Portugal, France, Britain and the Low Countries through Germany, Italy and central Europe to the Balkans. It reaches southern Sweden but is absent from Ireland, and it has disappeared from Latvia and, for a time, Denmark. Outside Europe it occurs in Turkey, the Caucasus and parts of the Middle East. In Britain it is mainly found in south-east England, with London and its suburbs a stronghold.

Its key need is dead wood in contact with the ground. Old oak woodland, wood pasture and parkland are classic habitats, but stag beetles also thrive in hedgerows, orchards, cemeteries and gardens where old stumps, roots and buried logs are left to rot. Oak is a favorite, but the larvae also use beech, lime, willow, ash, fruit trees and many other broadleaf species.

What do stag beetles eat?

The two stages eat completely different food. The larvae feed on decaying wood underground, chewing their way through stumps, roots and buried logs softened by fungi. This slow, nutrient-poor diet is why they take so many years to grow.

Adults hardly feed at all. They have a soft, brush-like mouthpart and drink sap oozing from damaged trees and juice from fallen, overripe fruit. The males’ great jaws are useless for eating. Adults live largely on fat reserves built up during their long larval life.

Behavior: flying, fighting and mating

Adult stag beetles appear in late May or June. On warm, still evenings, males take to the air at dusk, flying slowly with their bodies held almost upright and making a loud, low buzz. They are searching for females and for sap flows. Females fly less and spend more time on the ground or near dead wood.

When two males meet, they wrestle with their jaws, each trying to grip the other and lift or throw him off a branch or log. These contests decide which male gets to mate with a nearby female. Despite the drama, fights rarely cause serious injury.

When disturbed, a stag beetle often stays still or rears up with its jaws open as a warning. Males are harmless; females can give a painful nip but are not dangerous.

Life cycle and lifespan

After mating, a female digs down into soil next to rotting wood and lays a few dozen eggs. The larvae that hatch are soft, creamy white and C-shaped, with an orange head and six orange legs. They can grow up to about 10 cm (4 in) long and communicate by rubbing their legs together to make faint squeaks.

The larval stage usually lasts about three to seven years, depending on temperature and food. A fully grown larva then builds a cocoon of soil and chewed wood, roughly the size of an orange, a little way from its food. It pupates in autumn, and the adult forms within weeks but stays underground through the winter, emerging the following early summer. Adults live only a few weeks; males die soon after the mating season, and females after laying their eggs. The full story is told in how long do stag beetles live.

Predators and threats

Adult stag beetles are eaten by magpies, crows, jays, kestrels and owls, and by foxes, badgers, hedgehogs and cats. Birds often eat only the soft abdomen, leaving the head and jaws behind. Woodpeckers and badgers dig out larvae.

The main human threat is the loss of dead wood. Tidy forestry, removal of old trees and stumps, clearing of hedgerows and building on old parkland and gardens all destroy larval habitat. Many adults are also killed on roads and by cats in towns.

Conservation status and protection

The stag beetle was assessed as Near Threatened in the IUCN European Red List of saproxylic beetles (2010), because it is declining in the north and center of its range even though it remains widespread. A later assessment for the Mediterranean region classed it as Least Concern.

It is listed in Annex II of the EU Habitats Directive, which requires member states to designate special areas of conservation for it, and in Appendix III of the Bern Convention. In the UK it is protected from sale under Schedule 5 of the Wildlife and Countryside Act 1981 and is a priority species for conservation.

Anyone with a garden can help by leaving old stumps and roots in the ground and by burying logs upright in a “log pyramid” or “log pile” so the lower part rots in the soil. Volunteer surveys in several European countries collect sightings to track the species.

How to tell stag beetles from look-alikes

Male stag beetles are unmistakable in Europe, but females and larvae are often confused with other species.

Stag beetle larvae are often dug up by accident in gardens, in old stumps, under logs or in compost and leaf mold that contains buried wood. They feed only on dead wood and do not harm living plants, so they are best covered over again where they were found.

Myths and facts

Myth: stag beetles are dangerous. Males cannot bite hard with their long antlers, and even a female’s nip is only briefly painful. Stag beetles have no venom or sting.

Myth: stag beetle larvae eat plant roots. They eat only decaying wood. The grubs that damage lawns and roots belong to other beetles, such as chafers.

Fact: the adults are the shortest part of the life cycle. The beetles seen on a June evening have spent several years underground and will live only a few weeks more.

Fact: tidiness is the biggest threat. Removing dead wood, stumps and old trees takes away the only food the larvae can eat.

Stag beetles and people

With its striking antlers, the stag beetle has long fascinated people. Albrecht Dürer painted a detailed watercolor of one in 1505. In German it is the Hirschkäfer and in French the lucane cerf-volant, and in many countries it is a flagship species for the conservation of old woodland and dead wood.

Compared with tropical giants such as the Hercules beetle, the stag beetle is modest in size, but it is one of the best-known insects in Europe and a reminder of how many species depend on wood that people once considered waste. It belongs to one of the most diverse animal groups on Earth, described in how many beetle species are there.