Hermit beetle (Osmoderma eremita)

Also known as:	Russian leather beetle

Kingdom	Animalia
Phylum	Arthropoda
Class	Insecta
Order	Coleoptera
Family	Scarabaeidae
Genus	Osmoderma (1)
Size	Length: 2.3 – 3.9 cm (2) Larva length: 7.5 cm (2)

The hermit beetle is classified as Near Threatened (NT) on the IUCN Red List (1), and is listed on Appendices II (priority species) and IV of the European Habitats and Species Directive (3). It is also listed on Appendix II of the Bern Convention (3).

The hermit beetle (Osmoderma eremita) has a classic beetle shape and is large with glossy, dark brown elytra. The males have a pronounced groove through the centre of the pronotum, but it is much less conspicuous in females. Males release a pheromone to attract females which smells similar to leather, earning the beetles the common name of Russian leather beetle (2).

The hermit beetle is found throughout Europe, but not in the British Isles (1).

This species inhabits tree hollows that contain large amounts of loose, dead wood. The hermit beetle occurs in any tree species with suitable hollows, with oaks being the most important tree species, followed by lime trees, willows, beech and fruit trees (4).

Known as the hermit beetle since the entire life cycle can take place within the hollow of just one tree, this elusive species spends three to four years as a larva, feeding on the rotten wood in the centre of the hollow (2). It pupates in autumn, constructing a cocoon out of its excrement and wood mould, and then emerges as a beetle the following summer (4). Dispersal is limited, as although the beetles can fly, very few do, and even then, rarely further than 100 metres. For this reason the beetles require a stable environment with suitable habitat very nearby (2). Usually, adult hermit beetles are found from July to September (4). In field studies, the lifespan of adults has been up to one month, while in the lab, hermit beetles, especially females, may survive much longer (4).

The most important predator of hermit beetle larvae is probably the larvae of the click beetle (Elater ferrugineus), and they can also be infested with mites and nematodes. Occasional predation by vertebrates on hermit beetles has also been reported (4).

The loss of trees with suitable hollows is the greatest threat to this beetle. In managed forests, trees are cut down before any hollows are formed. Therefore, most sites where hermit beetles live today are situated in agricultural and even urban landscapes. Even in these habitats, hollow trees are cut down because they are no longer used (for example, pollarded trees and in plantations of fruit trees or chestnut trees), or to protect humans from accidents (2) (4). In addition, many hollow trees found on pasture woodlands, where gazing has now ceased, suffer from increased competition from younger trees. In many areas, the formation of new suitable trees occurs at a much slower rate than the deterioration of suitable trees, and there is often a great distance between the new trees and dispersal sources, resulting in fragmented hermit beetle populations that are more vulnerable to local extinctions (4).

Whilst the hermit beetle is a priority species of the Habitats Directive, protection is poorly enforced. Removal permission is generally granted without a hermit beetle search, and only trees that are known to have hermit beetles living in them are protected. Since hermit beetles are rarely obvious on the outside of the tree, populations are often not found until the tree has been felled (2).

Conservation measures need to include the preservation of remaining natural forest, to preserve and restore habitats connected with historic agricultural landscapes, and to preserve any remaining suitable habitat in urban areas (4). The hermit beetle serves as an ‘umbrella’ species for other hollow-dwelling species since it is better known, and protecting it will result in overall protection for this important habitat type (2).

For further information on the hermit beetle: 

• The Hermit Beetle:
  www.eremit.net
• Ranius, T. et al. (2005) Osmoderma eremita (Coleoptera, Scarabaeidae, Cetoniinae) in Europe. Animal Biodiversity and Conservation, 28(1):1–44. Available at:
  www.bcn.es/museuciencies_fitxers/imatges/FitxerContingut6653.pdf
• For further information on deadwood see WWF:
  www.panda.org/downloads/forests/deadwoodwithnotes.pdf

Authenticated (14/04/08) by Dr. Thomas Ranius, Associate professor, Swedish University of Agricultural Sciences, Uppsala.
http://www.ekol.slu.se/ShowPage.cfm?OrgenhetSida_ID=9090

• Elytra: in beetles and earwigs, the hard fore wings. They are held aloft when the insect flies, and are often coloured or patterned.
• Larva: stage in an animal’s lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
• Pheromone: a chemical produced by an animal, which stimulates a behavioural or physiological response by another member of the same species.
• Pollarded: a pollard is a tree with branches which have been cut back to the trunk so that is may produce a dense growth of new shoots.
• Pronotum: in insects, the hardened cuticle on the upper surface of the first thoracic segment (the part of the body nearest the head).
• Pupates: the process of forming a pupa, the stage in an insect’s development when huge changes occur that reorganise the larval form into the adult form.
• Vertebrates: animals with a backbone.

1. IUCN Red List (February, 2011)
   http://www.iucnredlist.org
2. The Hermit Beetle (November, 2004)
   http://www.eremit.net
3. National Biodiversity Network (November, 2004)
   http://nbn.nhm.ac.uk/nhm
4. Ranius, T et al. (2005) Osmoderma eremita (Coleoptera, Scarabaeidae, Cetoniinae) in Europe. Animal Biodiversity and Conservation, 28(1): 1 - 44. Available at:
   http://www.bcn.es/museuciencies_fitxers/imatges/FitxerContingut6653.pdf