Efforts in the wild

Sadly, the great capricorn beetle is today one of Sweden’s most endangered species. Only a small population remains at Halltorp nature reserve on the island of Öland. For this reason, Kalmar county administrative board was asked by the Swedish Environmental Protection Agency to come up with a national action plan for the great capricorn beetle.

Great capricorn beetle larvae develop over about five years under the bark and sapwood of very large oaks whose southern and western flanks are exposed to the sun. The adult beetles crawl out of the old oaks from mid-June to early July, depending on when the warm weather arrives in June. The adult beetles often fall prey to birds such as jackdaws and great spotted woodpeckers. This is why most great capricorn beetles don’t live long in the open. A few adult individuals have nevertheless been spotted well into August.

Since 2004 the county administrative board has commissioned an annual count of exit holes made by great capricorn beetles at Halltorp. The hatching holes are counted up to a height of four metres. The number of holes per year varies from about 20 to 40. Some holes might be missed, but the county administrative board has concluded that the population is worryingly small. You can see the results of these inventories in Table 1.

To get an idea of the genetic variation within the Halltorp population, samples will be collected from 25 individuals and DNA obtained from them analysed. The genetic variation will then be compared with populations in Poland and possibly Germany.

The large old oaks still alive at Halltorp represent only a small remainder of the oak woodlands that existed in the area until about a century ago. A tree inventory a few years back found 245 stumps of giant oaks (diameter > one metre breast-height). Today there are just ten living giant oaks at Halltorp nature reserve.

One of the action plan’s long-term objectives is to re-establish the great capricorn beetle on the mainland in Kalmar and Blekinge counties, where the species died out during the 1960s. In preparation for this, tree inventories have been carried out in the two counties. The inventories will be completed in the next few years and the results analysed. Areas will be proposed where the beetle can be reintroduced, and there will then be a dialogue between affected landowners, the county administrative board and the Swedish Forest Agency.

Jonas Hedin
Ecologist
Kalmar county administrative board