Stag beetles

by Richard Jones

It was getting dark, the cat was skulking after something in the shadows around the hutch and the guinea pig was squealing its head off...

Stag beetle and lesser stag beetleIt was getting dark, the cat was skulking after something in the shadows around the hutch and the guinea pig was squealing its head off. Something sinister on the patio? No, just another stag beetle.

I often say how privileged I feel to have these wonderful creatures in my back garden. South London is now about the only place in the UK where you can regularly see these awesome monsters. My supposition is that when the housing boom spread across the area 100 to 150 years ago, it was one of the most wooded parts of what was then Surrey. And although much of the land was under cultivation, this was a time of small fields bounded by tree-lined hedgerows. The houses went up in an era before bulldozers so each street was built piecemeal. Any large trees that didn't have to be removed were left in place; although few remain, their stumps and fallen logs are still present in the gardens and the rotting subterranean timber is still feeding the stag beetle larvae.

The target of the cat's interest and the pig's alarm was a female. These lack the huge antler jaws of the male but still are impressive beasts. And the small jaws are just as likely to give a nip if she's picked up less than cautiously. I've heard an anecdotal report that female stag beetles are more likely to be found crushed on pavements, the reason put forward being that people might know the male, but mistake a female for a cockroach or other nasty and deliberately trample it.

Lesser stag beetle, Dorcus parallelipipedus.I was particularly pleased to find this beetle, because I can now show it beside its smaller relative: the lesser stag beetle, Dorcus parallelipipedus. Like the 'true' stag beetle, Lucanus cervus, it has grubs that feed in fallen logs, but it reaches adulthood in only one or two years, rather than three to seven. Neither sex has large jaws, but females have two small bumps on the forehead, where the males' foreheads are flat.

Because dead wood is so poor in nutrients, it not only takes years for the maggots to accumulate enough body mass to turn into beetles, but their eventual body sizes vary greatly too. The stag beetle can be 25 - 75mm long, the lesser stag 20 - 30mm. There is an overlap, where very small female stags can actually be the same size as very large lessers. In these extreme cases, the ID guides tell us, look at the back legs. Stag beetles have three thorn-like spines on the rear tibia, lesser stags have only one or two.

Dorcus is much more widespread in Britain than Lucanus, and will feed on much smaller logs, so is much more likely to turn up in gardens away from south London.

The Great Stag Hunt

Stag Beetle Helpline

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Gardeners' World Web User 27/06/2008 at 00:41

Thank you Richard. At last, a picture of a female stag beetle. It's usually the male that gets all the publicity so people don't know what the female looks like. Even in last year's excellent article in GW magazine, there were pictures of males and larvae but no females. No wonder people squash them.

Gardeners' World Web User 30/06/2008 at 09:35

Reply to Barbara: It often says in rather dry turgid monographs that an insect might feed on "decaying organic matter", because when things really rot down there is not much difference between dead wood, compost, manure, carrion and dung. Any many insects can be found in any or all of these substrates. Stag beetles, like other insects breeding in rotten wood, are there because they can survive on the low nutrients in the decaying timber where other species can't. But maybe they have found an alternative niche in your friend's compost bin. I've often wondered whether the touted stag beetle bins (bottomless wooden crates half embedded in the soil and filled with wood chippings) actually work. But if they like the compost in Bournemouth...who knows. Thanks for the information.

Gardeners' World Web User 22/09/2008 at 13:58

The info about stag beetles is really interesting. I have loads of beetles in my garden, at the moment I can't identify them, but I wondered if anyone had a picture of a ground beetle and a picture of a vine weevil so I can compare and contrast, and only stomp on the vine weevil. At the moment I am leaving everything alone as I am not sure what is what.

Gardeners' World Web User 28/11/2011 at 18:36

I have a friend living in Moordown, near Bournemouth and she has Stag beetles in her compost bin. They are there all the time.