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Mortality in stag beetles (Lucanus cervus)

By Deborah Harvey, 26 October 2001 and updated on 5 September 2003.

Results of a survey of 600 corpses sent in the summers of 2000-1 suggest that the main predator of the stag beetle is the magpie, with over 50% of both male and female beetles falling victim to these distinct black and white birds.

The magpie leaves its victim in a characteristic way: head, thorax, elytra and legs intact and, perhaps most horribly, able to move for anything up to several days.
Click here for a view of a magpie victim.

The magpie typically takes its victim, as it emerges: swooping down to take the beetle as it emerges from the soil. The result is often a sorry sight with tens of corpses being left in a small area.

Of course, the magpie is not the only culprit stag beetles fall prey to; other predators include foxes, badgers, bats, cats, hedgehogs, grey squirrels, frogs, toads and other species of birds.
Again each has its own trademark.
Cats tend to bite through the tough exoskeleton but not actually kill or dismember the beetle, although the delicate legs may be ripped from the body.
Foxes and badgers tend to ingest the whole beetle, with remains of mandibles etc being found in the droppings.
Hedgehogs rip away the abdomen, leaving the elytra jagged; they also damage the thorax and may bite off the head.
Grey squirrels leave just wing cases and the head, often scattered around a tree.
Frogs and toads apparently swallow a beetle whole.
Smaller birds also tend to nip off the head, leaving the beetle intact.

Humans had killed many beetles in this sample, accidentally or otherwise, with many either having been trodden on or killed on the road. From this sample, there does not seem to be a sexual bias. Others are found drowned in swimming pools, ponds, rivers and water butts, perhaps attracted by their own reflection.

Of course, not all beetles meet an untimely end, with some dying naturally at the end of the summer season.
An investigation of the females in this group revealed that over 50% had not laid their eggs, or some of their eggs at least, which poses more questions than it answers.

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