Leatherjackets are the larvae of the European Crane Fly or Daddy Long Legs as they are commonly known. The larvae cause damage to lawns by feeding on the roots of grass plants.
Adult crane flies hatch from pupae in late July and August and lays their eggs in the ground within 24 hours of hatching. The larvae hatch about 2 weeks later and start to feed on grassroots, which continues through winter and into spring. They stop feeding in May/June when they will pupate in the soil. In general, they stay underground in the day and move up to the turf leaves at night. They are very sensitive to drying and do not survive if they are dried out by the sun. On very cloudy days when the turf is wet, you can see the larvae in the turf. They are about 25mm long and have grey/brown leathery skin.
Damage to lawns occurs from autumn to spring but is most severe in the spring when the leatherjackets are fully grown. Symptoms may appear as yellowing, weak areas of grass where the roots have been damaged. The grass can be easily pulled up with little or no root growth. Damage is usually more severe when the previous autumn has been mild and wet. Secondary damage can also be caused by birds and mammals digging up turf in their search for leather jackets.
The time to control the insects is when they are in the larval stage, not flies. They can be controlled by removing by hand or applying a biological nematode, which attacks the larvae, killing them within a few weeks. They are specific to the pest concerned therefore safe for the user, children, pets, wildlife and the environment. The main season for application is late August until the end of October. A spring application can be made in the case of severe infestations if the soil temperature is over 10 degrees Celsius.