The UK Stag Beetle

Stag beetles are Britain’s largest beetle. The species we have in the UK is Lucanus Cervus. The males are easily recognisable by their ‘antlers’ – these are in fact enlarged mandibles. The females do not have the enlarged mandibles and are slightly smaller.

Stag beetles show a wide variation in size. Males can be from approx. 3.5 to 7.5cm in length. The females show similar variation but are generally smaller (they can be as small as 2.3cm). However, the stag beetle is the adult form of the species and cannot grow – smaller beetles are not younger than the bigger ones and are not capable of growing any bigger. We don’t know why there is such a large variation in size and this is one of the areas my research hopes to address.

The adult beetles are only a very small part of an extremely long life cycle, surviving only months at best. Their sole purpose is to mate and lay eggs. They appear in early summer, and are most often seen flying on balmy summer evenings. Beetles don’t seem to need to feed.

The larva can take up to six years to develop before they pupate and change into adult beetles. They live below ground in rotting wood, upon which they feed. Pupation is very short, and the beetle emerges in late autumn but remains underground until the following summer.

Stag Beetle Info

Common NameStag Beetle
Latin NameLucanus Cervus

There are large gaps in our knowledge of the stag beetle in Britain If you find a stag beetle please help by filling out the Monitoring form.

We know that….

*The life cycle of the stag beetle is centred on rotting wood.

*Most people are familiar with the adult beetles, particularly the males with their prominent mandibles, which appear in the summer searching for a mate and a breeding site.

*After mating the female seeks out a suitable location to lay her eggs. This might be a rotting fence post, tree stump, log pile, or even a compost heap.

*The female lays her eggs in or near rotting wood.

*The larvae take 4-6 years to reach full size.

*During this time they feed on rotting wood.

*When fully developed, the larvae migrate to the surrounding soil where they pupate.

*After a short period the adult beetle metamorphoses and spends the winter in the soil, emerging in the following summer to mate and lay eggs.

Stag Beetle Facts

Are stag beetles and their larvae poisonous?
Definitely not! If frightened the beetles might give you a nip which may bruise but that’s all. As would any pet!

Do the larvae kill trees or spread fungus around a garden?
No! The larva feed on dead wood and they don’t spread any fungus around the garden.

I think I have found a stag beetle larva, how can I be sure?
There are many species of coleoptera (beetles), which have larva like that of the stag beetle.

I have found a stag beetle that seems to be injured, what should I do?
Stag Beetles have a very short adult life, so it is likely that they will die whatever you do. However, a small shallow container such as a milk bottle top with a mixture of honey and water may help.

Is it ok to keep a stag beetle as a pet?
Definitely not! The whole point of the stag beetles adult life is to mate, so by putting it in a box you are stopping this.

What do stag beetles eat?
Stag beetles may lap up honey and eat bits of fruit but they don’t tend to eat as their adult lifespan is very short. You could build a log pile to provide a perfect habitat for them.

The main predators to stag beetles are magpies, they leave the beetle in a characteristic way, just head, thorax and wing cases, with some or all of the legs. The beetles can survive like this for up to several days. Many people find beetles like this and are very distressed about it and curious to know why it has happened.

Other predators include, foxes, (they eat them whole and bits are found in the pellets) other birds, bats, hedgehogs and cats – which tend to puncture the beetle then lose interest rather than kill them. Then of course there’s man – not a predator but he kills many every year by destroying the habitat, running the beetles over, and perhaps the worst of all – deliberately stamping on them!