Farming practices across the UK led to the decline of the short-necked oil beetle. But the conservation charities RSPB Scotland and Buglife sent researchers to the island of Coll.
They were surprised to discover over 150 of the beetles on survey sites, a 400 per cent increase on the last count carried out in 2010. Until 2008, short-necked oil beetles were thought to be extinct in the UK.
However, recent surveys established there are two small populations - one in Devon and the other on Coll. The population in Devon is now stable, although numbers are significantly lower than on Coll.The beetle, which is named for the toxic oil secretions it produces when threatened, emerge in the early spring and immediately begin feeding on a wide variety of vegetation. After feeding on buttercups and other low growing plants, the beetles mate and the females begin the process of digging a burrow and laying over 1000 tiny orange eggs which hatch in a few weeks.
Once the eggs have hatched, the young larvae crawl on to vegetation, and wait to hitch a lift on a passing solitary bee in order to reach the bee's nest. The oil beetle larvae then eat the bee's egg as well as the protein-rich pollen the bee provides to its own larvae, emerging as a fully formed beetle the following spring.
James Silvey, Nature Recovery Officer at RSPB Scotland, said: "It is fantastic to discover so many on Coll and a good sign that the population is healthy and continuing to grow."