Black Oil Beetle
The Black oil beetle Meloe proscarabaeus is a beetle that I’ve looked for on Salisbury Plain before but not found until just recently. It gets its name from its habit of secreting droplets of ‘oil’ from its knee joints when roughly handled. This contains the odourless and colourless toxic chemical compound cantharidin which can cause blistering.
There used to be eight species in the UK but sadly three of them are now considered extinct. In fact two of our remaining five, the short-necked oil beetle Meloe brevicollis, last recorded in 1948, and the Mediterranean oil beetle Meloe mediterraneus, last recorded in 1906, were also thought to be extinct but were recently rediscovered by amateur entomologists in Devon.
Oil beetles rely on solitary mining bees to complete their life-cycle. The female beetle lays her eggs (up to a 1000) in burrows dug into soil near to where there are bees digging their own burrows. The eggs quickly hatch into leggy black larvae called triangulins which climb up the stalk of flowers (typically yellow flowers like lesser celandine and dandelion) and lay in wait hidden amongst the flower petals.
When an unsuspecting solitary bee visits the flower to collect nectar and pollen for its own nest the larvae climb aboard secured by their specially-adapted hooked feet. Once transported to the bee’s nest, the triungulin feed on the bee’s eggs and its store of pollen and nectar. The larva develops in the bee burrow until it emerges as an adult oil beetle ready to mate and start the whole cycle again.
Oil beetles have been identified as priorities for conservation action through the UK Biodiversity Action Plan (UKBAP) – meaning work needs to be done to conserve them and their habitats.