The Cockchafer, or ‘May Bug’ is a large beetle that can look rather alarming, but is not usually a huge problem for gardeners.
The larvae of this beetle can do some damage to plant roots, however, and so is sometimes considered to be a minor garden pest. And it can do more damage if it appears in large numbers.
In this article, we will discuss this beetle in a little more depth, and take a look at what to do if these beetles – or more likely their larvae – are causing damage in your garden.
What is a Cockchafer Beetle?
The common cockchafer, Melolontha melolontha, also known as the ‘May Bug’ or ‘May Beetle’, is a European beetle that was once abundant throughout Europe.
It could be a major pest when in mass flight, but was almost entirely eradicated by pesticide use by the middle of the 20th Century.
While locally exterminated in some regions, its numbers have resurged in some places since pesticides began to be more tightly regulated in the 1980s.
This species is fairly common in the south of the British Isles but rarely found further north.
You are likely to see the adult beetles in May and June, when they emerge and live for around 5-7 weeks. It is fairly common to hear them crashing into windows when they are attracted to the light at night.
The female adult cockchafer lays her eggs around 10-20cm deep in fields or lawns or garden beds after a couple of weeks, and the larvae will hatch around 4-6 weeks later.
They feed on plant roots and will live and develop in the soil for 3-4 years, overwintering 20-100cm below the soil surface and working their way to the surface each spring.
They will grow to be up to 4-5cm long before they pupate in early autumn and develop into adult beetles over around 6 weeks.
Due to their long lifecycle, cockchafers will appear in a cycle every 3-4 years, and every 30 years or so they can appear in much higher numbers.
What Cockchafer Look Like
The adult cockchafer or May bug is around 2.5-3cm long, with a brown colouration on its wing cases and legs, and a black thorax.
The larvae are plump, creamish-white grubs with brown heads which can grow to up to 3-5cm in length.
Is the Cockchafer a Problem in UK Gardens?
It can occasionally become an agricultural pest, though is not one of the more troublesome pests in most gardens. Adults beetles do eat both flowers and leaves, but rarely do so to a degree which becomes a problem in UK gardens.
You may find that they damage a few leaves – typically on trees such as oak, maple, sweet chestnut, beech, plum and walnut. But this feeding is rarely enough to be a major problem in the UK.
In small numbers, cockchafer grubs can cause a little damage to roots in lawns, vegetable plots or garden borders. Lawns can also be damaged by predators looking to eat them.
However, they are generally considered less of a problem than other chafer grubs, such as the garden chafer (Phyllopertha horticola) and Welsh chafer (Hoplia philanthus) which can do a lot more damage – especially in lawns.
And the larvae only become a serious problem and become a troublesome agricultural pest where they are found in very large numbers.
Usually therefore, there will be no need to get rid of Cockchafer from your garden. Often, you can simply live and let live. And this is generally the best policy in an organic garden.
When Cockchafers Are a Problem
If you identify the large larvae of cockchafer beetles in your garden when digging or preparing new beds, and have experienced plant losses due to their root-eating ways, then there are a few things you can do to solve this problem.
Attract Cockchafer Predators
One important approach for any organic garden involves the control of pest species by making sure that the ecosystem is in balance.
Attracting plenty of predatory creatures to your garden will help to keep the larvae numbers down and keep your plants safe.
In the case of cockchafer beetle larvae, rooks are a major predator that you want to have around.
The larvae are sometimes known as ‘rookworms’ because these birds are said to really like to eat them.
Attracting plenty of birds to your garden can be a key strategy in organic pest control. Rooks and other corvids will be attracted to roost at the top of tall trees, like elms for example.
So where there is space, planting trees can be a wonderful idea.
Consider placing some wax worms or other ‘treats’ on a bird feeder to encourage corvids to your garden and plant to make sure there are nutrient-rich food sources for a range of birds in your garden through autumn and winter.
Remove Larvae By Hand
Digging up an area and removing larvae by hand is another option, though of course this can be time-consuming and difficult.
Removing the adults has not been shown to be particularly effective, but removing larvae could solve the problem in immediate terms.
However, disturbing the soil in your garden is not really a good idea. When you disturb the soil it will also impact a wide range of beneficial organisms and disrupt the soil web. And it could make your garden less healthy overall.
Where cockchafer larvae are a big problem, though this is rare in the UK, there are also biological controls to consider.
However, it should be remembered that eradicating a species from your garden entirely is hardly ever a good idea.
Like other species, the cockchafer has a role to play in the ecosystem. Unless they are found in large numbers, they are not usually a massive problem in UK gardens.
A permaculture garden designer, sustainability consultant and freelance writer, Elizabeth works as an advocate for positive change. She aims to inspire others to reconnect with nature and live in a more eco-friendly way. She also tries to practice what she preaches as she tends her own forest garden, polyculture beds and polytunnel. See her personal website here.