Scientific Name: Melolontha melolontha
Other names: Maybug, Rookworm
The fat white larval stage of the Cockchafer Beetle is quite destructive to cereal and other grass plant roots. They live in the soil for three or four years and are sometimes called Rookworms as Rooks are said to be particularly fond of adults and larvae. The adult beetles are up to 35mm long and can fly making them a little frightening as they buzz around, usually at dusk in May, but are harmless to humans. The adults are also destructive, feeding on flowers and foliage.
They are usually found in rough grazing or cereal crops and in new gardens. They will cause yellowing of the grass in a similar way as Leatherjackets. Also the turf can be damaged by birds such as Starlings, Magpies and Crows as they dig for the grubs; and badgers can be very destructive, leaving a trail of small craters.
It should also be noted that the larva of the much rarer Stag Beetle is quite similar to the Cockchafer grub, but it is found in decaying wood, especially oak.
Turning over the soil exposes them to the birds, as does watering and covering with polythene overnight to bring them to the surface. The biological control which uses a parasitic nematode called Heterorhabditis megidis is not effective against the Cockchafer grub, but will kill the grubs of the common Garden Chafer which is much smaller, but similar in shape with legs on the thorax.
The Garden Chafer, right, is much smaller.
For chemical control Provado Lawn Grub Killer which contains *Imidacloprid is a recent introduction for the treatment of Leatherjackets and Chafer Grubs.
Picture of an adult Maybug about 30mm long.
*Imidacloprid is a neonicotinoid compound and these have been suggested as as causative agents of colony collapse disorder (CCD) in Honeybees. The neonicotinoids have been shown to get into pollen and nectar, and the European Food Standards Authority has produced a report warning of the danger to bees. Some of the leading DIY chains in the UK have stopped selling Provado Lawn Grub Killer, and the neonicotinoids are already banned in some countries in continental Europe with a possible EU two year ban to be voted on in spring 2013.
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