About stag beetles
Stag beetles are one of the most spectacular looking insects in Britain, named because the male’s large jaws look just like the antlers of a stag. As well as being one of the largest (it can grow larger than a matchbox in size), they are sadly one of our rarer beetles. Stag beetles and their larvae are quite harmless and a joy to watch.
A stag beetle’s head and thorax (middle section) are shiny black in colour and its wing cases are chestnut brown.
Male adults appear to have huge antlers, almost half the size again of their body. These appendages are actually over-sized mandibles, used in courtship displays and to wrestle other male beetles. They are not harmful to humans. Adult males can vary in size from 35mm – 75mm long and tend to be seen flying at dusk in the summer looking for a mate.
The female adult beetles are smaller at between 30-50mm long, with normal sized mandibles. They are often seen on the ground looking for somewhere to lay their eggs.
A fully-grown stag beetle larva (grub like) can be up to 110mm long. They are fairly smooth skinned, have orange head and legs and brown jaws. They are nearly always found below ground up to half a meter down.
The beetle that is most often mistaken for a female stag beetle is the lesser stag beetle. A large lesser stag beetle can be similar in size and shape to a small female stag beetle. However, the lesser stag is uniformly black all over with matt wing cases, while the female stag beetle has shiny brown or maroon wing cases. Lesser stag beetles tend to have a much squarer overall look. Cockchafers can be of a similar size to lesser stags and are active on warm nights in May and June, but can be distinguished from stags by their ribbed wing cases and covering of hair.
The stag beetle has a very long life cycle lasting at least four years and possibly up to seven.
Once they have mated, the females lay small, round eggs below ground in rotting wood, particularly log piles, rotting tree stumps and old fence posts.
These larvae feed on the decaying wood around them for at least three years after which they will begin to pupate into adults.
They build an ovoid-shaped cocoon in the soil, up to 50cm below ground, that can be as large as an orange and take up to three weeks to build.
Within it the larva will pupate and metamorphose into an adult, emerging from their cocoon in the autumn and spend the winter and spring in the soil.
Around the middle of May the adults begin to emerge above ground, males a little earlier than the females. By the end of August, as summer fades, most of them will die. Very few survive the rigours of winter.
During their short adult lives the male stag beetles will spend their days sunning themselves in an attempt to gather strength for the evening’s activities of flying in search of a mate. This is when you are most likely to spot them.
Larvae feed on decaying wood. Adults have not been seen feeding but do take moisture from ripe fruits.
Woodland edges, hedgerows, traditional orchards, parks and gardens.
Predators such as cats, foxes, crows, kestrels and others may also have an adverse impact at the most vulnerable stage in the beetle’s life cycle, when adults are seeking to mate and lay eggs. Though this is largely natural predation, it has been suggested that the rise in the numbers of magpies and carrion crows in the last decade may be having a significant impact on stag beetle populations.
The most obvious problem for stag beetles is a significant loss of habitat. Many woodlands were sold for development in the inter-War years; just think of all the suburbs built since the 1920’s. the introduction of the Green Belt in 1947 did restrict suburban expansion but since then many of London’s surviving open spaces have sadly been developed, including many woodlands. development will continue to reduce stag beetle habitats, but increased awareness of their existence can help defend the beetles against developers.
In addition the ‘tidying up’ of woodlands, parks and gardens has led to the removal of dead or decaying wood habitats which is the stag beetle larvae’s food source. tree surgery operations such as stump-grinding of felled trees removes a vital habitat for the beetle. Although ‘tidying up’ still continues in gardens, woodlands and park managers are now much more aware of the need to retain dead and decaying wood as part of the woodland ecosystem. the Royal Parks’ management plans for Richmond Park, and other Royal Parks, include the retention of suitable dead wood to help encourage stag beetles to settle.
Humans are, unfortunately, a direct threat to the stag beetle. Adult beetles are attracted to the warm surfaces of tarmac and pavements, making them particularly vulnerable to being crushed by traffic or feet. Stag beetles have a fearsome appearance and sometimes people kill them because they look ‘dangerous’. We need more volunteers to help with research so that we can further understand these intriguing insects.
Changes in weather patterns are also likely to have an impact on our Lucanidae friends. exceptionally dry or wet weather is likely to substantially affect the larvae. Wet and windy weather can inhibit adult beetles’ flying ability.
Status and conservation
The stag beetle is a ‘protected species’, which is listed on Schedule 5 of the Wildlife and Countryside Act 1981. If stag beetles and/or stag beetle larvae are known or thought to be present at a site where an application for planning has been submitted,and are likely to be disturbed or destroyed whilst work is carried out at the site, it is recommended that someone with an understanding of the insects’ requirements be present to see that any larvae and/or adults are carefully translocated to a suitable natural or purpose-built habitat close by. Download our stag beetle fact sheet for more information about planning and development.
Stag beetles have been recorded throughout much of Western Europe, including Britain (but not Ireland), though in many countries they are now thought to be very rare or even extinct. However they are still relatively widespread in southern England, especially the Thames Valley, north Essex, south east Suffolk, south Hampshire and West Sussex. They are also found in the Severn valley and coastal areas of the southwest. Elsewhere in Britain they are extremely rare or even extinct.
Dead wood is not the only prerequisite for stag beetles. They prefer light soils as females have to dig down to bury their eggs and newly emerging adults have to find their way to the surface. Therefore, areas like the North and South Downs, which are chalky, have very few stag beetles. In these areas, they occur only in ribbons along river banks which are often lined with old trees such as oak.
Stag beetles prefer the areas of Britain which have the highest average air temperatures throughout the year and the lowest rainfall. It is not surprising, therefore, that they are mostly restricted to the south-east with small populations in a few areas in Devon and Worcestershire.
We are particularly keen for people to record stags in the counties on the border of their known range including Cambridgeshire, Devon, Gloucestershire, Lincolnshire, Norfolk, Warwickshire, Worcestershire and Yorkshire. Please keep a special eye open if you are visiting the following places: Richmond Park, Wimbledon Common, the New Forest and Epping Forest.
Useful stag beetle links
Website dedicated to stag beetles from our partners at Royal Holloway, University of London
Stag beetle video
Short film of stag beetles in action from the Natural History Museum.
Database of insects and their food plants
This database is primarily a collation of published interactions between Great Britain ‘s invertebrate herbivores (insects and mites) and their host plants. DBIF aims to help researchers access the accumulated knowledge of British plant-herbivore interactions, which is otherwise scattered throughout a vast published literature.
Stag beetle mites
Article from the Suffolk Naturalists Society newsletter, by Colin Hawes.
Development of non-invasive monitoring methods for stag beetles
Article from Insect Conservation and Diversity, by Harvey et al.
A collaborative conservation study across Europe
Article from Insect Conservation and Diversity, by Harvey and Gange.
Bionomics and distribution of the stag beetle across Europe
Article from Insect Conservation and Diversity, by Harvey et al.