On sunny spring days look out for black sausage-shaped beetles crawling slowly over the short grass.

These large insects are oil-beetles, named because they can exude oily droplets when alarmed.

Their wing-cases look far too short for their fat bodies, so they resemble portly gentlemen who’ve outgrown their dinner-jackets.

Some of the species are very rare or local; the one you’re most likely to see in spring is the black oil-beetle (Meloe proscarabeus).

It’s an impressive insect, with females reaching lengths of 33mm.

Keep an eye for them between late March and May on short turf on downs and commons or along paths and cliff-tops, when sadly, many are trodden on.

The females lay their eggs in burrows in the turf and when they hatch, a bizarre life-cycle begins.

Thousands of tiny larvae emerge from the eggs; they are long and thin and very un-beetle-like, with legs that end in a small cluster of claws.

Hitching a ride

They scramble to the top of flower stalks and sit in the open blossoms, waiting for a solitary bee to arrive.

When it lands, they swarm on to it grabbing with their tiny claws, but they don’t harm the bee.

What they’re after is a free ride back to the bee’s nest burrow.

The lucky larvae that reach a nest feed on the bee’s egg and its store of pollen, pupate in the burrow, and emerge the following spring.

Oil beetles are declining in many places, possibly because the solitary bees are also in decline.

The invertebrate conservation charity Buglife is keen to know about any you find.

Take part in the Big Spring Watch – we need your help to record how fast spring is spreading and how our wildlife is coping.

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Thank you to Springwatch Flickr group contributors for the use of their images.

Illustration by Rose Sanderson