Oil Beetle

Meloe proscarabaeus

18-40mm

March to early June

Large flightless beetle, most likely to be encountered along coastal paths including cliff-tops. Named for the ability to exude a yellow or orange oily liquid from the leg joints. Oil Beetles occur only in areas with a good mix of wildflowers and solitary mining bees, but in these areas can be very frequent when the adults emerge in spring – sometimes up to ten beetles being seen in a two metre stretch of path, but always very localised. The females are much larger than males, with gravid abdomens. 

Large female - Coastal cliff path, Isle of Wight. April

The male antennae exhibit a very noticeable cupped section about halfway along their length, and the abdomen often tapers more than the blunt tail end of the female.

Adults are black with a blue sheen and pitted texture all over the head thorax and elytra.

 Three females and smaller male below

Each female can lay around 1000 eggs which she deposits in a burrow. The fast moving hatchling larvae are known as Tringulins and clamber to the tops of flowers in vast numbers to hitch a ride on various solitary bees. Once taken back to the nest burrow of the bee, the larvae develops into a more grub-like, typical beetle larvae, feeding on the eggs and pollen stores of the bee. 

 Very large female, just over 40mm long

When the mature larvae pupates it will remain hidden within the host’s burrow until the following spring. When the adults emerge they feed on the foliage of various low growing plants. A similar species is M.violaceus, which has a stronger blue sheen, more finely pitted texture and is found in a wider northern area than M.proscarabaeus. 

Spot the male and female!

This pair had been mating by the side of a coastal path, April 2014

Within a few feet, there were at least 9 others, and one crushed on the path