Volunteers from the SVA and Sid Valley Biodiversity Group had the real pleasure of helping the 1st Sid Vale Cubs explore the nature on Peasland Knapp Nature Reserve and to build a ‘Bug Hotel’ last Monday. The highlight on the sunlit evening was that now is the time to see one of our most intriguing insects and we weren’t disappointed.
The Guardian newspaper is running a series to promote awareness of the unsung invertebrate heroes of nature. One of the contenders for Invertebrate of the Year lives in Sidmouth, can be seen at this time of year, and has a remarkable life story, the Black Oil Beetle.
The Black Oil Beetle is a large insect and looks like it is wearing a black waistcoat that is too tight because its wings do not develop fully and the large abdomen protrudes. Most beetles in the UK can fly to disperse, having underdeveloped wings doesn’t hamper the Oil Beetle because its babies fly by hitching a ride on bees to spread out.
The beetles are most often found in meadows and other grassland with a good variety of wild flowers where they spend most of their year long lives underground as larvae known as triungulins because they have three tiny claws on each foot, and that is vital to their story.
The triungulins pupate over winter and the adult beetles emerge on sunny days in spring feeding on plants such as Lesser Celandine and Dandelion and searching for a mate. The females then dig a small burrow and lay their eggs underground, nothing unusual there, but the next stage is extraordinary.
When they hatch in May, the triungulins emerge and seek out a flower, again Celandine and Dandelions are among the favourites. They climb the flower and wait. If a bee visits the flower, the triungulin hooks into the bee’s fur and is carried back to the bee’s nest. The bee needs to be one of the solitary mining bees, ones that dig a nest tunnel in bare patches of muddy ground.
The triungulin is taken inside the nest by the unwitting bee but it is not a polite house guest. It feeds on the bee pollen store. When that is exhausted, the voracious predator eats the eggs and bee pupae as well. It will then pupate and undergo metamorphosis, ready to emerge next spring and start the process again.
Nature is harsh, obviously the bees suffer but there are usually enough of them about to keep the population going. This is vital for the beetles, if there are no mining bees, the beetles will die out as well.
The combination of SVA conservation work and the week of bright sunshine has made Peasland Knapp an ideal home for Black Oil Beetles. A large patch of bramble was cleared recently using a heavy duty mechanical mower. This has allowed other flowers including Celandine to flourish. Several large ant mounds have been scalped by the mower to leave bare patches of soil. This is ideal for the mining bees and there was a male Grey-patched Mining Bee sat on a mound close beside the adult Oil Beetles. On Monday the Cubs reaped the benefit, they gained a memory that will stay with many of them for a long time. Hopefully it will trigger some to become life long naturalists.
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