Crane Fly Damage in Lawns

- Crane fly larvae damage turf at the roots -

Summary: Crane flies resemble very large mosquitoes. Adults are harmless but the larvae of some species can damage the roots of your lawn. Control treatments should be applied in the fall to kill young larvae.

Jack DeAngelis, PhD
OSU Ext. Entomologist (ret.)

This page will help you identify and get rid of turf-damaging crane flies in your lawn. While most crane flies are harmless, the European crane fly can damage and even kill patches of lawn. New lawns are especially susceptible because their root system is not yet well-developed. Crane fly larvae feed in the root zone during winter months and this is why it is best to control crane fly larvae in the fall before significant root damage occurs.

Crane fly identification

Both adults and larvae are fairly easy to identify. Adult crane flies are medium-large insects that resemble large mosquitoes (right) [picture of crane fly adult] but are harmless. Like all fly larvae, crane fly larvae [picture of crane fly larva] lack a distinct head and legs. Since they feed on plant roots they are found in soil, just below the surface, in the root zone.

Most crane flies prefer damp soil and are common around stream and lake edges. A few species, however, have adapted to relatively dry soil and can therefore attack turf and lawn areas.

common names: mosquito hawks, "helicopters", leatherjackets, daddylong legs

crane fly adult and larva

Line drawing of crane fly adult and root-feeding larva. Larva is about 1" long.

Crane fly damage

Crane fly larvae feed on grass roots but a few larvae will not cause noticeable injury to healthy grass. High numbers, however, can cause so much root injury that the grass no longer can get the water and nutrients it needs and the turf dies as the weather warms in summer. You'll see large, irregular patches of dead grass when this occurs.

The injury threshold is usually considered to be 25 larvae per square foot; however, this will vary depending on overall turf health. To determine larval density dig a square foot (12"x12") area of turf and look for larvae in the root zone just below the soil surface.

Most turf damage occurs between late fall and the following spring. Adults emerge during summer and lay eggs that hatch into root-feeding larvae. Young larvae that occur during the fall are also the easiest to control.

Crane fly control

Since healthy lawns can sustain considerable crane fly damage there are only two situations where routine insecticide applications may be needed. First, new lawns that lack a robust root system can be severely damaged if infested with crane flies so fall applications of insecticides may be needed during the first fall after planting. Secondly, commercial turf areas (golf courses, athletic fields, and so forth) where scouting has revealed a larval density greater than 25 per square foot. Lawn insecticides that are labeled for white grub control are often approved for crane fly control as well. However, read product labels carefully to ensure that crane fly is listed (see White Grub Control in Lawns).

Caution: treating lawns with insecticide can be risky. You should take precautions to avoid contaminating nearby water but also apply enough overhead irrigation to wash insecticides into the root zone, Also, crane fly larvae that have ingested insecticide can be poisonous to birds that feed on these larvae. Many bird kills have resulted from excessive insecticide applications targeted at crane flies.

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