We have two species of Stag Beetles in the UK, the Lesser Stag and the larger and rather more impressive Stag Beetle. Lesser Stags are reasonably common, but the Stag Beetle is  listed as ‘Nationally Scarce’ in Britain and is at risk all over Europe. If you come across a community of Stag Beetles, the likelihood is that they will be the smaller of the two species.

Stag beetles are the largest of all our beetles here in the UK with the male of the species reaching 7 cm long at maturity. This entire group of beetles gets their name from the impressive set of headgear that is sported only by the male Stag Beetle. He wears a set of antlers – actually enlarged and modified mandibles – that he uses, not to chew or bite with, but to grasp and toss his rivals when trying to win a mate. Modified as they are for this purpose, the poor old male Stag Beetle has to rely on sips of sap or the juices of rotting fruit for occasional nourishment in his adult life-stage as his jaws, magnificent as they look, are no longer suitable for chewing.

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Both male and female Lesser Stags are of similar size and they look like smaller versions of the female Stag Beetle. The female Stag Beetle is 5 cm long in comparison to the 2 to 3 cm of her smaller cousins. Stag Beetles have a semi-gloss exoskeleton with a dark chestnut coloured wing case while Lesser Stag Beetles are a dull black all over in their adult attire.

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Both species of Stag Beetles have a similar life-cycle. The females lay their eggs in rotting wood and once the eggs hatch the larva feed on the wood until they are large enough to pupate.  They then build themselves a cocoon within which they metamorphose and emerge as adults. This much they have in common. However the details and timings of their life-cycles are very different.

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When Greater Stag Beetle larvae emerge from their eggs, they spend  up to five years feeding on rotting wood to attain the size they have to reach before pupating. While a Lesser Stag larvae can reach a respectable 8cm long in two years, Stag Beetle larvae grow to a whopping 11 cm long. That is one very plump grub! The grubs of both species are creamy white with orange-brown heads and legs, and brown jaws.

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Adult Stags rarely live for more than one summer, though they can occasionally last through a winter. Lesser Stags have a longer adult life stage, and they spend most of their time with their offspring underground or near the surface of soil near rotting wood rather than above ground as Stags adults do. Lesser Stag adults can be spotted in and around the soil and rotting wood, in cracks and crevices on walls and trees or flying towards lights at night.

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Counting Stags with Ginger

Scientists have had great difficulty mapping the distribution and population of stag beetles around Britain because, by the very act of searching for these subterranean beetles, they would be at risk of further destroying their habitat.  They had to find a way to be able to locate stag beetles without disturbing and potentially damaging them.

It was already known that many invertebrates that nest in or feast on rotten wood are attracted to the scent of a chemical called   alpha copaene, so  ecologists set about finding a cheap and easy source of this chemical and they found it in avocado, mango and ginger.  Using powdered ginger – because it is the cheapest of the three – the scientists bated traps and found that Stag Beetles and their larvae were indeed tempted by the scent. This was great for monitoring the adult population, but they were still left with the problem of finding out if any larvae were present underground.

 

This they did with miniature microphones. It turns out, that along with crickets and grasshoppers and many other invertebrates, the larval stage of the stag beetle communicate with each other by rubbing their legs together, much as crickets do when they rub their wings together to ‘sing’. This stridulating is distinct to each species so by listening to the sounds being emitted from within rotting wood, ecologists found they could determine, not only the presence of a grub, but which species of grub it was. With these two curious methods of finding and monitoring Stag Beetles around the UK it is hoped that this rare and endangered species can be protected and saved from extinction.

 

• Neither Stag Beetles nor Lesser Stags eat sound wood and they will not harm buildings. On the contrary, they are a valuable part of the garden and countryside ecosystem, breaking down rotting wood and processing fungi.

• You are most likely to spot Stag and Lesser Stag males on warm, thundery summer evenings. They used to be known as Thunder beetles as they choose these humid nights to make their mating flights in search of a female.

• Lesser stag beetles play dead if they feel threatened but Stag Beetles don’t.