Insects are the most species-rich group of animals in the whole world, so too in Sweden and in the Royal National City Park. The type of setting that is most renowned for its special and rare insects in the park is an area with large old trees, especially the ancient oaks in Djurgården and Ulriksdal.
The abundance of ancient oaks in the Royal National City Park is responsible for the wealth of insect species there. The broad-banded oak-bark longhorn beetle, Plagionotus detritus, is an example of an extremely rare beetle which in Sweden only occurs in Djurgården and in Haga. The species lives in recently deceased oaks. The dead and dying oak wood is suitable as a habitat only for one or two years before the beetle must find a new colony tree. With luck, you might see this wasp-like beetle during warm June days around Stora Skuggan. Attempts are underway to re-establish this longhorn beetle in other old forests (especially in the Båtfors area of Uppsala County) by introducing – over a couple of years – individuals which come from existing groups in Djurgården.