How to identify a cockchafer May bug

19 May 2014

It isn't actually a bug and doesn't only fly in May, but the UK's  largest chafer beetle is easy to spot.

Seen for the first time, an adult cockchafer, or May bug, can cause a bit of a stir and people can be worried by them. 

But Stuart Hine from the Museum’s Identification and Advisory Service (IAS), who is often asked by the public to identify them, confirms that they most certainly don't sting. 

'They have a segment called the pygidium at the end of their abdomen, which is long and pointed,' Hine said. 'It looks vicious but is actually a tool for females to lay eggs into the ground.'

segment called the pygidium at the end of their abdomen, which is long and pointed.

Cockchafer abdomen segment, pygidium, is long and pointed but not for stinging.

Adult cockchafers are one of the top enquiries to the IAS during May. 'We would usually expect to get 100 or more calls from people wanting to know what this peculiar creature is,' said Hine.

Cockchafers, Melolontha melolontha, are relatively large beetles belonging to the scarab family. Adults are 2.5-3cm long, and are common in the south of England and the Midlands. The name cockchafer means 'big beetle' in Old English. 

Although one of their common names is the May bug, if climate conditions are right, adult cockchafer beetles are often seen flying in April. 

Museum Coleoptera Curator Beulah Garner said a warm spell, such as we've had this spring, will bring them out early. 'They've certainly been seen in April this year around the country.'

A cockchafer with its distinctive orange fan-like antennae

Distinctive orange fan-like antennae © NaturePlus/Anton69

Cockchafers have whitish triangles on their sides, hairy bodies, reddish-brown wing cases that meet in the middle and orange fan-like antennae.

Noisy neighbours

Adult cockchafers only live for about 5 or 6 weeks. During that time, they look for a mate and fly into the tree tops to feed on leaves. They fly at dusk on warm evenings, making a noisy hum, and are attracted to light.

‘They sometimes mistake chimney stacks for tree tops and occasionally fall down chimneys into open fireplaces,’ Hine said. 'Then after dark, they are attracted to light and can get caught in lamp shades.'

Not bugs

Although they are known as bugs, cockchafers are not true bugs, which belong to another group of insects that includes shield bugs, water bugs, aphids and scale insects. 

True bugs that can fly have wings that usually overlap when folded, instead of meeting in a mid-line as cockchafer wings do.

The larva, or grub, of the cockchafer can grow to up to 40mm.

Larvae live underground for 3 or 4 years and grow up to 4cm. © Rasbak, Creative Commons

Life underground

Cockchafers spend most of their lives (three to four years) underground as larvae, or grubs. The grubs are white and C-shaped with six legs and reddish-brown heads. 

They can be larger than the adults, growing to up to 4cm and are a food source for owls and bats.

Grubs eat the roots of a variety of plants and in large numbers can become pests damaging pastures and crops.

Summer chafer

Another common species to look out for is the summer chafer, Amphimallon solstitialis. This is a smaller species that usually emerges at the beginning of June and is common around the date of the summer solstice, 21 June. 

'It does pretty much the same thing,' Hine said. 'It flies around tree tops, nibbles leaves as adults and eats roots below ground as a larva. It is also prone to falling down chimneys.'

  • This story has been updated from the 2011 version.
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