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What do stag beetles eat?

Do stag beetles eat?
No, they can't eat any solids. Their enormous antlers are enlarged mandibles which are totally useless for eating, but can give you the odd pinch, of course.
They might have the odd drink though.
Indeed, in my experience, they are rather partial to sweet juicy fruits. As you can see below the beetle is very interested in the melon.

Male stag beetle enjoying a ripe juicy melon, MF 2003.

Then, how do they drink?
Just look at a close up view of a male stag beetle mouth parts.

Side view of a male stag beetle drinking from a piece of melon, MF 2003.

Can you see two yellow feathery bits just about touching the melon?
Well, the beetle sucks the juice with those tubes, just as we might use two drinking straws. The female mouth parts are just the same, except for the smaller antlers.

How is it that they can live without eating?
Stag beetles have enough fat reserves to keep them going; they have been accumulated by their larvae during their very long life underground.

In the wild stag beetles, as well as other insects, are attracted to sap runs, which are very sweet. See below stag beetles congregated on a oak tree with a sap run. There is only one female, she is the one feeding on the sap.

Female stag beetle at sap, plus 3 males, 26 June 2006. Photo by Gerrit Rekers.

Click on the picture to see a slide show of the interesting action around that sap run.
Photo taken on 26 June 2006, by Gerrit Rekers, Veluwe, The Netherlands.

Other stag beetle species also feed on sap, for one from South America click here.

Stag beetles may also drink from rotting fruit and are known to like cherries. Cherry-eaters is indeed an old English name for stag beetles. See below a photo of a male stag beetle enjoying the juices of an overripe cherry (Prunus avium).

Male stag beetle holding a cherry, 19 July 2005. Photo by John T. Smit.

Photo taken on 19 July 2005, by John T. Smit in a sunken lane
(holle weg in Dutch), near Etzenrade, Limburg, The Netherlands.

John writes: "There were four males feasting on the cherries lying on the ground. The male on the photo is not actually carrying it, but rather defending it against me. He was using his mandibles to turn it around so that he could reach the juices from one of the cracks in the skin".

Adult stag beetles do not grow any more, eat no solid food and will do no damage in your garden.

LINKS:
Stag beetle feeding on a plum - Video posted in YouTube.
Would you like to see some good drawings of insect mouth parts? Then click here.

REFERENCES:
Hawes, C. (2004) Stag Beetles at Sap. White Admiral, 57.
Hongo, Y. (2005) Diurnal activity of the Japanese stag beetle Prosopocoilus dissimilis okinawanus Nomura (Coleoptera, Lucanidae). Elytra, 33: 245-257. [PDF]
Krenn, H.W., Pernstich A., Messner T., Hannappel U., Paulus H.F. (2002) Kirschen als Nahrung des männlichen Hirschkäfers, Lucanus cervus (Linnaeus 1758)(Lucanidae: Coleoptera). Entomologische Zeitschrift 112/6: 165-170.
Nash, D. (2003) Red Admiral Butterflies at Sap. White Admiral, 56.
Ratcliffe, B.C. (1970) Collecting slime flux feeding Coleoptera in Japan. Entomological News 81: 255-256.

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