Black oil beetle © Guy Edwardes/2020VISION
Black oil beetle
This impressive beetle digs burrows, lays thousands of eggs and has bee-riding larvae.
Scientific name
Meloe proscarabaeusWhen to see
February - JuneSpecies information
About
The black oil beetle is mainly found on coastal grasslands with lots of wildflowers, as well as lowland grasslands further inland and occasionally heathlands or woodland sites. Adults appear early in the year, in February or March. They feed on grasses and the leaves and petals of flowers, fattening up as they prepare to breed.Oil beetles have an unusual lifecycle. Females dig burrows and lay huge numbers of eggs inside them. When the eggs hatch, the larvae (called triungulins) leave the burrow and climb onto a nearby flower. They wait for a bee to arrive (usually a solitary bee) and grab onto it, hitching a ride back to the bee's nesting burrow. Once inside a bee's burrow, a triungulin will eat the bee's own eggs or larvae, as well as the pollen stored up for them. The young beetle will stay in the burrow, pupate and emerge as an adult the following spring.
How to identify
The black oil beetle is a large, plump beetle that is usually found walking ponderously across the ground. It is black, often with a violet-blue sheen. The wing cases on its back overlap each other and are shorter than the abdomen, making it look like it's wearing a jacket that's too small for its body.It is very similar to the violet oil beetle. The most reliable way to tell them apart is to look at the rear edge of the thorax (the section of the body directly behind the head). In the black oil beetle, the rear edge is almost straight. In the violet oil beetle, there is an indentation. If in doubt, get a good photo of this part of the body and a beetle expert can help to identify it.