Leatherjackets

What it is

Leatherjackets are the larvae of crane flies, the long-legged insects that blunder into houses in late summer. Several species are involved, but the common European crane fly does most damage. The grubs live just below the soil surface and feed on roots and stem bases, especially in lawns on damp, heavy soils after wet autumns.

Symptoms

Lawns develop yellow, then brown patches in spring and early summer that do not green up with rain. Starlings, rooks, crows and badgers peck or dig at the turf to reach the grubs, which is often the first sign. The grubs themselves are greyish brown, legless, tough-skinned and up to about 3 cm long. In vegetable beds, young plants are cut off at soil level. Chafer grubs cause similar lawn damage but are white and C-shaped with legs.

Cause

Adult crane flies emerge mainly in late summer and early autumn and lay eggs in grass. The larvae hatch within a couple of weeks, feed through autumn and mild spells in winter, then feed hard in spring before pupating in early summer. Wet weather in late summer and autumn favours egg survival.

Control

To check, soak a patch of lawn, cover it overnight with black plastic or damp sacking, and lift it in the morning to count the grubs that surface; dispose of them or leave them for birds. A drench of the nematode Steinernema feltiae is the main non-chemical treatment, applied in early autumn while soil is warm and moist. Rake out dead grass and reseed bare patches once grubs are dealt with. There are no sensible chemical options for home lawns.

Prevention

Improve drainage on wet lawns by spiking and top dressing. Encourage birds and ground beetles. Before turning old grass into a new vegetable bed, dig it over in autumn and early spring so birds can pick out the grubs.

Plants often affected

• Lettuce
• Strawberries

Could it be something else?

These problems share some of the same symptoms. Compare them, or run the symptom checker with these signs ticked.

• Allium leaf miner
• Carrot fly
• Onion fly
• Slugs and snails

Months to keep an eye out: January, February, March, April, May, June, September, October, November and December.

Sources

Identification and life-cycle details were checked against the references below. Text and advice are our own. See our editorial policy.

• Wikipedia — Tipula paludosa
• Wikipedia — Crane fly