The Other Beetle
The Other Beetle, Less well known than ground beetles, rove beetles have long, slender bodies and tiny wing cases. Val looks at how they help gardeners.
MOST gardeners recognise ground beetles by their hard wing cases and oval bodies. Many beetles are big and black, although we do love the violet ground beetle (Carabus violaceus), which is almost an iridescent purple in sunlight. Most of the time ground beetles are sheltering in the vegetation, and this is why my garden is packed with plants that cover the ground. I want to encourage these excellent predators because the ground beetle is the best predator of the grey field slug (Deroceras reticulatum).
Both the adults and larvae of the beetle eat the slug and its eggs. This slimy, pinkish, plump slug is a real problem because it can overwinter and survive (and feed in) low temperatures. It’s the one you find above ground, in or on your lettuces, and the one that ravages oilseed-rape crops. However, there’s another type of beetle called the rove beetle (or Staphylinidae) and there are 950 British species. Many of them are predators. But they look entirely different from ground beetles because they have long, narrow bodies and tiny wing cases. The most well known of these beetles is the Devil’s coach horse (Ocypus olens), which looks terrifying. Several used to inhabit an outhouse in the winter months when I lived in Northamptonshire in the 1980s. If you got too close they raised their tails rather like a scorpion. I never actually saw them squirt any foulsmelling liquid from their abdomens, although they can. The Latin species name olens means smell. These nocturnal beetles feed on fly larvae, insects, spiders and slugs.
Smaller rove beetles tend to feed on the larvae of the cabbage root fly, and in the glorious days of the National Vegetable Research Station at Wellesbourne in Warwickshire, where I worked in the 1970s, nine species were found feeding on the immature larvae. Entomologists there found that rove beetles were twice as common as ground beetles close to brassica crops, although this census was carried out in May 1961 when there was an abundance of insect life. I can remember walking to school in the late 1950s one late September day and a section of privet hedge was festooned in hundreds of garden spider webs, and each one dripped with dew. That day has stuck in my mind for 60 years, but now I find only the odd one. Other rove beetles eat aphids, and Oligota flavicornis (sorry, there’s no common name) eats fruit-tree red spider mite. Going back in time this tiny beetle, measuring 1/25in in old money, was found to be numerous in Essex orchards in 1945. If those orchards are still there, sprays will probably have killed off both predator and prey alike.
sources:
Amateur Gardening, June 2018
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