Springtime means oil beetles

posted in: Cornwall Wildlife Groups | 1
Violet oil beetle
A violet oil beetle

Back in May, members of one of Cornwall Wildlife Trust’s Local Groups headed out in search of beetles, particularly a remarkable, distinctive but threatened creature that comes out in springtime as regularly as primroses, bluebells and celandines. They discovered specimens – both alive and, unfortunately, squashed.

If you go down to the woods in April/May, be very careful where you put your feet – especially on ground that’s been trodden flat or tightly grazed. Look out especially on paths near clusters of those shiny yellow, star-like celandines that brighten up bare earth in spring. April/May is the season of oil beetles, and they may be on a track near you.

The first violet oil beetle found on Cornwall Wildlife Trust’s Launceston Area Parish Wildlife Group’s (LAPWG) beetle hunt had already been trodden on. It was a male, and the female it had been courting was still alive, close by. Whether the two had already met, we shall never know.

Oil beetles can be as long and rounded as your little finger and they move very slowly, so they are much easier to spot than many of the myriad other beetles that cross your path. You may find the adults near nests of mining bees, which like sunny, often sandy ground or banks, with plenty of flowers nearby. They could be grazing on celandines, burrowing in the earth, where they shelter and lay their eggs, or bumbling around seeking a mate.

If you are sharp-eyed, you may see the tiny, stick-insect-like larvae crawling up celandine stems and waiting on the flowers for particular solitary bees to pass, so that they can hitch a lift (see photo). Flying through the air clinging to a bee is just one part of the extraordinary life story of the oil beetle. If the larvae have chosen the right species of mining bee, they eat its egg and pollen and transform to a grub-like stage, sheltering in the bee nest until the following year.

There are five different varieties of oil beetle in the UK, three of which you might see in spring. Another three have already gone extinct. In the valleys of the Tamar, the Lynher and their tributaries in East Cornwall, the most frequently spotted is probably the violet oil beetle (Meloe violaceus) which, although black as night, can have an exotic violet sheen. Other species, such as the black oil beetle (Meloe proscaeabeus) might be an inkier black, as if made from tar. Cornwall is a national stronghold for the black oil beetle, which is something to be aware of and to celebrate.

On really close inspection, oil beetle armour seems to be made of beaten metal, to varying degrees. Another odd feature is the drops of oil that exude from the beetle’s body. You may see tiny flies feasting on the oil (see photo).

Oil beetles seem to be quite oblivious to both humans and their dogs, which is why it’s so important to watch where you tread at this time of year in particular. They are locked into their oil beetle world, and have no intention of being distracted. Due to the long body, they seem quite ungainly, particularly the larger, fatter females.

If you do see oil beetles when you are out and about in the countryside, please take a photograph and report your sightings to the charity Buglife’s national oil beetle survey and to ORKS (Online Recording Kernow & Scilly, https:/orks.org.uk), run by the Environmental Records Centre for Cornwall and the Isles of Scilly and based at Cornwall Wildlife Trust. ORKS have a downloadable phone app for notification of all your wildlife encounters. Make sure the thorax (‘chest’ section’) is clear in your photograph, as this will help towards identification. Records are of vital importance for conservation work. Oil beetles are under serious threat due to changes in land use, and conservation organisations need to be aware of where they still exist in order to protect them. The oil they exude may cause irritation and the beetles themselves are easily dented and damaged, so do not touch the beetles when photographing them.

The LAPWG group had invited two beetle experts along, who helped identify the many beetles that were found along the way, in particular the large and distinctive Dor beetle but also many others including a large cardinal beetle larva (the adult is scarlet) and other beetles in shades of metallic copper and blue-green as well as black. Many local events, including minibeast hunts for families, are on the Trust website cornwallwildlifetrust.org.uk/whats-on, and further details are available from info@launcestonparishwildlife.org.uk

Local group contacts can be found on the Cornwall Wildlife Trust website cornwallwildlifetrust.org.uk, and many events are printed in the Trust’s Wild Cornwall magazine for members and supporters. You can create suitable habitat for mining bees and even oil beetles, simply by creating and maintaining flowery grasslands and lawns.

Violet oil beetle larva waiting on a celandine flower for a passing bee © Rowena Millar
Tiny flies on a violet oil beetle seen near Downgate, east Cornwall © Rowena Millar

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