Sensational Stag Beetles
The Stag Beetle Lucanus cervus is possibly the UK’s most iconic insect species, and it’s easy to see why. As well as being our largest land beetle (up to 8cm long!), the males grab attention with their namesake antler-like jaws. Find out more about these remarkable creatures from our resident expert Rory Dimond.
Male Stag Beetle © Clame Reporter (Wikimedia commons)
The male Stag Beetle’s red spiny jaws make him unmistakable. Although these may appear alarming, they actually have a weak bite and are harmless to humans. The females have a much smaller head and jaws but can nip if roughly handled. Both sexes have burgundy wing cases, clubbed antennae and long, black, spiny legs.
The similar and more common Lesser Stag Beetle Dorcus parallelipipedus is smaller and completely black, with the male bearing shorter jaws.
Female Stag Beetle © Simon A. Eugster
Male lesser stag beetle
Stag Beetles start life as a small, spherical egg, laid underground in decaying wood. Females will seek out a variety of deciduous woods, from Oak to Buddleia but it must be rotting, damp and host decay fungus to make it hospitable and digestible for the growing larvae. The pale, C-shaped grub has powerful jaws for munching away at the decaying wood, growing to 8cm long. However, it grows slowly and it can take 3 to 7 years to complete tits larval life. Once it is ready to pupate, the larva leaves the wood and burrows down to 50cm underground. Here it forms a protective cocoon of soil and waste matter the size of an orange around itself before pupating for several months.
Stag beetle grub preparing to pupate
The adult Stag Beetles start to emerge from May. Despite their long life so far, they now must race to breed. Their time feeding as a larva built up the beetle’s energy stores. Now, the adult male’s oversized jaws make him unable to eat solid food, so he is only able to sup from sap runs on damaged trees or fallen fruit juices as an energy boost. Mango, avocado and ginger can be used to attract hungry males lured by the chemical scents they give off.
On still, humid evenings, the beetles fly from their birthplace to find new breeding places and mates. As might be expected from such a large insect, the flight is clumsy and loud.
Males detect females by pheromones and fight over them. Facing off with heads raised and jaws agape, they judge the size of their opponents. When they appear well-matched, a wrestling match commences. The battling males attempt to grip and flip their opponent off the log and are so strong that one can lift the other up into the air. The winner gets to mate while the loser has to try his luck elsewhere, if he is not injured in the struggle. The mated female seeks cover and a place to lay her eggs, burrowing into soft soil.
The adult beetles will die off by August and many are taken by predators, including Foxes, Badgers, Crows, Magpies and Owls. The adult’s brief flight and struggles are all for ensuring the next generation. The important thing for their life cycle is that their deadwood habitat is left undisturbed for 10 years or more to allow the wood to decay and their larvae to grow.
Stag Beetles are at the Northern edge of their range in the UK, so are found mainly in the Southern and Eastern counties. Perhaps surprisingly, London is a national stronghold for Stag Beetles. This is likely due to the many old trees in the city’s parks and open spaces providing plentiful decaying wood. They are often found on the Heath at this time of year, so keep your eyes peeled when out and about! You don’t even need to visit open spaces to see one, as three quarters of records submitted to the ‘Great Stag Hunt’ survey were from gardens.
Unfortunately, Stag Beetles have undergone historic decline and are scarcer than they used to be. This is partly due to the tidying of parks and gardens leaving less breeding habitat, as well as loss of woodlands to development. They are now a Conservation Priority Species under the Wildlife and Countryside Act and legally protected from sale (as pets or specimens).
If you would like to help Stag Beetles on the Heath, you can adopt a Stag Beetle Loggery through our adopt a wildlife home scheme. You can also find out more about the Heath’s wildlife habitats here. And, new to our shop, you can now buy a Stag Beetle tote bag to support our largest insects!
Volunteers building a stag beetle loggery on Hampstead Heath
