How to identify a cockchafer May bug

18 May 2011

It doesn't only fly in May and it isn't actually a bug, but the cockchafer can be seen at the moment and is pretty easy to spot, being the UK's largest chafer beetle.  

The May bug, or cockchafer, is a common beetle in the UK and has made an early show in April 2011

The May bug, or cockchafer, is a common beetle in the UK and has made an early appearance in April 2011.

When seen for the first time, an adult cockchafer can cause a bit of a stir and lots of people find them a little worrying, according to Stuart Hine of the Natural History Museum’s Identification and Advisory Service (IAS)

Cockchafers, Melolontha melolontha, are relatively large beetles - in Old English 'cockchafer' means 'big beetle' - belonging to the Scarab Family. They are not true bugs. Adults are around 25-30mm long, and they are common in the south and Midlands of the UK.

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

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

Cockchafer abdomen segment called the pygidium is long and pointed but not for stinging. It is used by females to lay eggs in the ground.

Stuart explains why people are worried about them. 'This is probably because they have a segment called the pygidium at the end of their abdomen, which is long and pointed.' 

‘This is a tool for females to lay eggs into the ground,’ says Stuart. ‘They most certainly don’t sting.’

Noisy adults attracted to light 

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

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

Not bugs
A cockchafer with its distinctive orange fan-like antennae

A cockchafer with its distinctive orange fan-like antennae © NaturePlus/ Anton69

Although they are known as May bugs, cockchafers are not true bugs. True bugs are another group of insects that includes shield bugs, water bugs, aphids, scale insects and others. 

The true bugs that can fly have wings that usually overlap when they are folded, instead of meeting in a mid line as cockchafer wings do.

Appearing earlier in April

Although one of their common names is the May bug, this year adult cockchafer beetles have been flying mostly in April rather than May, according to enquiries to the IAS.

‘This year, adult cockchafers have emerged a little bit early, so we started to see them from the end of the first week of April onwards,' says Stuart. 'Traditionally you don’t start to see them until the end of April and beginning of May.’ 

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

The larva, or grub, of the cockchafer lives underground for around 3 or 4 year and can grow to up to 40mm. © Rasbak, Creative Commons

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

'The early emergence this year is almost certainly due to the warm weather at the end of March early April. 

'Many other insects have been forced into an early emergence also, which is not altogether a bad thing because many of the flowers and plants that they are associated with have also grown and flowered early.'

Most of life underground

Cockchafers spend most of their lives (3 or 4 years) underground as larvae, or grubs. The grubs are white and C-shaped with 6 legs and reddish-brown heads. 

They can be larger than the adults, growing to up to 40mm and are a food source for owls and bats.

Grubs eat the roots of a wide 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,' adds Stuart. '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.'

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