Violet Oil Beetles, Brook Wood

Field Paintings

A sure sign of spring over the last week has been the emergence of oil beetles in a favoured shelted sun-trap by the River Mardle. These bizarre insects can be seen wandering along the ground in their characteristic gangling manner.

They stop occasionally to devour the leaves and flowers of cuckoo pint, lesser celandine and cleavers. As the sun drops in the late afternoon they sunbathe on dead leaves for a while before hiding amongst the leaf litter for the night.

These beetles have a strange life cycle. The female lays thousands of eggs in pits dug in bare ground. These emerge after a few weeks as tiny very active larvae called triungulins. These climb onto flowers such as dandelions and climb onto any insect which visits the flower. The only ones which survive are those which hitch a lift on certain female solitary bees and are carried back to the bees’ nest. Once there the triungulin disembarks as the bee lays an egg onto a honey-filled cell.

The oil beetle larva then consumes the bee egg before changing its skin and becoming more maggot-like in form so it can feed amongst the liquid honey. It may devour several cells in the nest and when full grown it pupates in the burrow and emerges the following year as an adult oil beetle.

Buglife are conducting a survey of these beetles this year and are keen to hear from anyone who has seen one – more information go to

John Walters

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