Stag beetles are a group of about 1,200 species of beetles in the family Lucanidae, presently classified in four subfamilies.

A well-known species in much of Europe is Lucanus cervus, referred to in some European countries (including United Kingdom) as "the" stag beetle (it is the largest terrestrial insect in Europe). Pliny the Elder noted that Nigidius called the stag beetle lucanus after the Italian region of Lucania where they were used as amulets. The scientific name of Lucanus cervus is this word, plus cervus, deer. Male stag beetles use their jaws to wrestle each other for favoured mating sites in a manner that parallels the way stags fight over females. Fights may also be over food, such as tree sap and decaying fruits. Despite their often fearsome appearance they are not normally aggressive to humans. Female stag beetles are usually smaller than the males, with smaller mandibles. As larvae, females can be distinguished from males by the presence of cream-coloured, fat ovaries visible through the skin around 2/3 down the larva's back. The larvae feed for several years on rotting deciduous wood, growing through three larval stages until eventually pupating inside a pupal cell constructed from surrounding wood pieces and soil particles. In the final larval stage, "L3", the grubs of larger species, such as Prosopocoilus giraffa, may be the size of a human finger.

The mouthparts of stage beetles are made for sucking liquid food. Saps and rotten fruits are their favorites, such as Flame goldrain tree and Orange tree. They are often seen on these kinds of trees.

The adults seldom leave away from trees, no matter eating, matching or copulating and the larvae eat fiber structure of deadwoods for food. So you can easily see them in places with trees or forests.