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Leatherjackets are the larvae of crane flies, or daddy-longlegs. The female fly lays up to 300 eggs in the lawn in late-summer. These hatch after a couple of weeks into grey-black, legless larvae that have a tough, leathery skin, hence the name 'leatherjacket'. From autumn through to summer, the larvae feed on the roots of plants, eventually growing to 5cm in length before pupating and emerging as adult flies in late-summer.
Solution
Organic
After heavy rain or having thoroughly watered any yellow patches in the lawn, cover them with black plastic sacks and leave overnight. The leatherjackets will come to the surface and can be collected in the morning. Encourage natural predators, such as spiders and garden birds, especially starlings. Use the biological control Steinernema feltiae, which should be applied while the ground is still moist and warm in late-autumn.
Chemical
Treat the lawn with an insecticide containing imidacloprid from May to October.
