September bug of the month: Leather Jackets

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This month, Dr. Ian Bedford tells us everything we need to know about the 'bug of the month' for September, Leather Jackets.

Is there a problem with my lawn?

One feature that’s shared by many of Britain’s 23 million gardens, is an area of grass that we call the lawn. And, whether that lawn forms a garden carpet, or just a meandering pathway between flower beds and borders it’ll undoubtedly require some degree of management if it’s to remain as a lawn is not evolve into a mini meadow. Besides regular mowing though, this will entail trimming the edges, occasional feeding & weeding and if necessary, some watering. But in addition, if a lawn is to remain in a healthy condition, it’ll be useful to recognise the early signs of a problem so it can hopefully be nipped in the bud and dealt with accordingly.

The most common sign that a lawn has developed a potential problem, is the appearance of yellow patches where the grass loses its chlorophyll and begins to die. Although this could be the result of something being spilt on the grass, or where a dog has urinated, it’s more likely to be where something in the ground is eating and damaging the grass roots. The most likely culprit for this destruction is the tubular, greyish-brown grubs that we call Leather Jackets, the soil-dwelling larvae of Crane flies.

What are Leather Jackets?

Leather Jackets are the soil-dwelling larvae of Crane flies, also known as daddy-longlegs, usually seen at the end of summer. After mating, the female Crane flies settle on the lawn and begin laying their eggs into the ground. As the eggs soon hatch, the Leather Jackets begin to feed on the grass roots before hibernating underground throughout winter.

When do Leather Jackets start causing problems?

Once the ground starts to warm during Spring, the young Leather Jackets resume their feeding, and as they grow, they cause increasingly more damage to the lawn before finally pupating underground during mid-summer.

How should Leather Jackets be controlled?

Where infestations are large, lawns will often sustain significant damage, and Leather Jackets will need to be controlled. However, this should really be done in a way that doesn’t involve using broad-spectrum chemicals, since these can harm many beneficial creatures and the essential microbes that exist within and sustain a healthy soil.

Instead, microscopic nematodes (worm-like creatures), that are a natural parasite of Leather Jackets, could be watered into the affected lawn to infect and kill the grubs during late spring or early summer.

Otherwise, there’s another simple alternative that could be tried, which involves knowing that during their development, Leather Jackets move within the soil in response to the weather. When it’s sunny and dry they tunnel deeper within the soil, but when it’s raining and wet, they move up to the surface. So, by regularly watering a lawn throughout the warmer months, Leather Jackets will remain up near the surface and within easy reach of the Starlings, Crows and Gulls, that love to eat them.

About Dr. Ian Bedford

Ian has been fascinated by the bug world for as long as he can remember. From studying butterflies on the South Downs as a youngster, he went on to pursue a career in Research Entomology and ran the Entomology Dept at the John Innes Centre in Norwich up until his recent retirement. Ian now works as an independent entomologist offering advice to companies developing environmentally safer plant protection products.

Ian has also appeared in a number of TV and radio shows including BBC Gardeners Question Time, BBC Gardeners' World,Inside Out, BBC Breakfast and The Great British Garden Revival.

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