European stag beetle

Baby stag beetles eat rotting wood.

They live inside old logs and stumps under the ground. Grown-up stag beetles only lick sweet tree sap and juice from old fruit.

A stag beetle larva eats rotting wood. It lives in damp, moldy wood that touches the soil, such as old stumps, fallen logs and the roots of dead trees. Oak is a favorite.

Adult stag beetles cannot chew food with their big jaws. Instead, they lick up sweet sap that oozes from damaged trees, or juice from rotten fruit, with their tongue.

The larvae are xylophagous: they feed on rotten dead wood at ground level, under stumps and fallen logs or among the roots of standing dead trees. Oaks, especially English oak (Quercus robur), seem to be favorites, and larvae can also develop in the introduced northern red oak. A large stump can feed several generations of larvae for years, until it has completely broken down.

Adults cannot use their mandibles for eating. Both sexes take sap runs on tree trunks and other sugary substances, such as rotten fruit, which the Young People's Trust for the Environment describes them lapping up with their tongue.

On warm summer evenings, boy stag beetles fly.

They whirr slowly through the air, looking for girl beetles. They fly standing almost upright, because their jaws are so heavy!

Stag beetles are most active at dusk. On warm early-summer evenings, males fly around looking for females, buzzing slowly and clumsily with their bodies held almost upright. Females usually stay near the ground.

Many animals catch adult stag beetles, including foxes, magpies, crows, woodpeckers, kestrels and owls. Underground, wild boars and badgers dig up the larvae and pupae.

Adults are crepuscular, with a seasonal peak of activity, between late May and late June depending on the region, when males swarm at dusk in search of females. Males are often seen flying up to the canopy, while females mostly stay at ground level. Rink and Sinsch (2007) found that stag beetles fly between about 11 and 26 °C and inferred that flight is hindered above 27 °C.

Predators of adults include shrews, foxes, magpies, hooded crows, woodpeckers, kestrels and owls; wild boar and badgers are the main predators of larvae and pupae, and mites can attack beetles still in their emergence galleries. Researchers even monitor populations by counting the remains of beetles eaten by birds and mammals.

Stag beetles need old wood to grow up in.

When old trees and logs are cleared away, they lose their homes. Old logs and stumps in parks and gardens can be homes for them.

Stag beetles have become rare in some places. Their larvae need old, rotting wood in the ground, and many forests are now cut while the trees are still young, so there is less dead wood left. Hot, dry summers may also make life harder for them.

Stag beetles are protected by European Union law, and scientists have worked out ways to count them so they can tell whether numbers are rising or falling. Their larvae can grow up in parks, orchards and gardens wherever old wood is left in the soil for many years.

The species is listed in Annex II of the EU Habitats Directive, so member states must report on its conservation status every six years, and it is classed as Near Threatened on the European Red List of saproxylic beetles (Nieto and Alexander 2010). Its IUCN Red List assessments are regional rather than worldwide, and they differ: Near Threatened for Europe (2010) and Least Concern for the Mediterranean region (2017). Italy's national red list also rates it Least Concern.

Bardiani and colleagues name the main threat as the falling average age of trees in forests, due to intensive management and overexploitation, especially in eastern Europe, which removes the old trees and dead wood the life cycle requires. Rising predation by magpies, jays and crows near people, and warmer, drier summers that hinder flight and emergence, are further concerns. Standardized monitoring, such as dusk transect counts, now tracks populations.