The East European hermit beetle – the shining star of Ruissalo’s range of insects
The East European hermit beetle (Osmoderma barnabita) is a large, 3–4-cm-long, dark beetle. In Finland, the species is native only on Ruissalo, in addition to which it is sporadically found in some other locations within a few kilometres of Ruissalo. In other words, the species’ Finnish population lives in complete isolation from other European populations, and it is threatened, protected and classified as a protected species.
East European hermit beetles live in the hollows of old oaks and other aged deciduous trees, where their larvae eat decomposing leaf humus and other organic matter. The East European hermit beetle’s larval stage lasts 3–4 years. Adult beetles, by contrast, live for only a few weeks. Fully grown adults do not eat at all, focusing solely on reproduction. The males fight over females by pushing each other.
The East European hermit beetle population of Ruissalo has been studied by Matti Landvik, whose excellent doctoral dissertation Isolated in the last refugium ‒ The identity, ecology and conservation of the northernmost occurrence of the hermit beetle was published in 2018.
