By Andrew Halstead reviewed by Andrew Salisbury edited by Steve Head
The most important beetle families with species that feed on live plant roots are the Scarabaeidae
, subfamily Elateridae
or click beetles and Melolonthinae
or chafers, and the Curculionidae or weevils (also discussed under leaf-eating beetles
). In all cases, it is the larval stage, rather than the adult beetles, that feed on roots. Some are important garden pests.
Species in Britain and Ireland
Seventy three species of Elateridae beetles have been recorded in Britain and Ireland. The adult beetles are commonly known as click beetles and the larvae as wireworms. Some click beetle larvae develop in rotten wood or in the soil in habitats other than gardens. Some are garden pests, particularly some Agriotes and Athous species. Apart from the pests, it seems little attention has been given to these species in gardens.
The larvae of chafer beetles, of which there are 16 species in Britain and Ireland, are known as chafer grubs. As with wireworms, some chafer grubs develop in rotten wood, but there are some garden pests. These include the garden chafer, Phyllopertha horticola, cockchafer or Maybug, Melolontha melolontha and the Welsh Chafer, Hoplia philanthus. The last mentioned occurs in England and Wales, particularly in sandy soil districts. Chafer grubs are sometimes found at the bottom of compost heaps. These are larvae of the rose chafer, Cetonia aurata, which is not a pest species as the larvae feed on rotting plant material.
There are over 430 weevils, with many developing as larvae in the soil, but only a few cause significant damage to cultivated plants. The principal culprit is the vine weevil, Otiorhynchus sulcatus.
Click beetle larvae, known as wireworms, are slender elongate grubs up to 25mm long. They are yellowish brown and have three pairs of short legs at the head end, with a fleshy protuberance on the underside at the rear end. Adult click beetles are slender in form with a marked "waist" between thorax and abdomen. They have a peg-like structure on the underside of their thorax that fits into a cavity on the abdomen. If an adult click beetle finds itself threatened or upside down, it flexes its body, storing energy, and releases the peg with an audible ‘click’ sound, and flexing the abdomen. This flips the beetle into the air, giving it the opportunity to land right way up - or to escape predators. The mechanism is described here
. Like the cuckoo, it is one of the few animals that can ‘speak’ its name.