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Crane Fly Damage in Lawns
- Crane fly larvae damage turf at the roots -
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Summary: Crane flies resemble large mosquitoes. Adults are harmless but the larvae of some species damage the roots of lawn grasses. Control treatments should be applied in the fall.
Jack DeAngelis, PhD
OSU Ext. Entomologist (ret.)
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 This page will help you identify and get rid of turf-damaging crane flies. While most crane flies are harmless, European crane flies can damage and even kill patches of lawn. New lawns are especially susceptible because their root systems are not well-developed. Crane fly larvae feed in the root zone during winter months. This is why it is best to control crane fly larvae in the fall before significant root damage is done.
Crane fly identification
Crane flies are medium-large insects that resemble large mosquitoes (right) [picture of crane fly adult]. Adult crane flies are harmless. Like all fly larvae, crane fly larvae [picture of crane fly larva] lack a distinct head and legs. Larvae feed on plant roots.
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
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| Line drawing of crane fly adult and root-feeding larva. Larva is about 1" long. |
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Crane fly damage
Crane fly larvae feed on grass roots. A few larvae will not cause noticeable injury to healthy grass. However, high numbers cause so much root injury that the grass can no longer get the water and nutrients it needs and the turf dies as the weather gets warm and dry, usually in summer. You'll see large, irregular patches of dead grass when this occurs.
The commonly cited injury threshold is 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 the easiest to control.
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Crane fly control
Since most healthy turf and lawns can sustain considerable crane fly damage there are only two situations where routine insecticide applications may be needed. New lawns that lack a robust root system can be severely damaged if infested with crane flies. Fall applications of insecticides may be warranted during the first fall after planting. Secondly, commercial turf areas (golf courses, etc.) 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 European crane fly is listed.
Caution: treating lawns with insecticide can be very 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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Crane fly workshop
Download this free slide set for additional informaton.
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Mission: To provide accurate, up-to-date and unbiased information for solving common insect and mite problems around your home, business and landscape using least-toxic methods.
Jack DeAngelis, Ph.D.
Please see the Disclaimer statements as well (sorry, but these really are necessary).
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