Bionomics and distribution of the stag beetle, Lucanus cervus (L.) across Europe.

1. The European stag beetle, Lucanus cervus, is thought to be widely distributed across its range, but a detailed description of its occurrence is lacking. 2. Researchers in 41 countries were contacted and information sought on various life history characteristics of the insect. Data on adult body size were collected from seven countries. 3. Habitat associations differ between the United Kingdom and mainland Europe. Larvae are most commonly associated with oak, but the duration of the larval stage and the number of instars varies by up to 100% across Europe. 4. Adult size also varies; beetles from Spain, Germany, and the Netherlands are larger than those from Belgium or the UK. In the former countries, populations are composed mainly of large individuals, while in the UK, the majority of individuals are relatively small. Allometric relations between mandible size and total body length differ in Germany compared with the rest of Europe. 5. Distribution maps of the insect, split into records pre- and post-1970, from 24 countries are presented. While these inevitably suffer from recorder bias, they indicate that in only two countries, Croatia and Slovakia, does the insect seem to be increasing in range. 6. Our data suggest that the insect may be in decline across Europe, most likely due to habitat loss, and that conservation