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European Crane Fly & Common Crane Fly 
By Sharon Collman, EPA

What is a crane fly?

Crane flies are generally beneficial two-winged flies that look a bit like large mosquitoes. Despite their somewhat scary appearance, they don't bite, suck blood, or carry diseases. In fact the adults are harmless and rather comical as they bounce around the landscape and off interior walls. They are also an important food source for birds and other critters. The aquatic larvae of many crane flies are indicators of good stream health, and become fish food. Other crane flies are decomposers and help break down decaying organic matter.

So why all the fuss about crane flies?

Two species of crane fly have adapted to feeding on grasses and the roots of some plants. There have been cases where, over a period of several years, they became so numerous that lawns were completely stripped of grass. Bare soil, where there was once lawn, made good media headlines and had a strong impact on the minds of turf-conscious gardeners. Gardeners assume crane fly is the cause of any unhealthy looking lawn. However, serious damage only occurs to some lawns in an area; it often builds up over several years. The exception is when it this crane fly is new to an area, or when it arrives with heavily infested sod. There is usually plenty of time to check lawns and intervene if the numbers begin to build. In fact, often even heavy infestations disappear because the eggs dry out or birds, parasitoids, and little organisms in the soil eat larvae.

Is there any good news about crane flies?

The adults and larvae are great bird food: in fact starlings and robins often completely control lawn populations. There are also a lot of other natural enemies of the larvae that attack them through winter (e.g. native nematodes, microorganisms, parasitoids, frogs, and small insectivorous mammals). Adults are eaten by birds, bats, cats and yellowjackets, etc. Turf researchers in Washington and Oregon, say, "only one in ten lawns will get crane fly, and only one in 100 will need to be treated". With a little effort, you can tell if you have them (see the "numbers game" below) before they get way out of control.

When do I look for crane fly larvae and adults?

Larger larvae can be found in the top three inches (3") of turf (and sometimes in flower beds especially near the lawn) in spring. With a shovel, turn over the sod and look. Adults emerge and are weakly attracted to lights in late summer and early fall and may get into the house by mistake. There they soon die.

Look for the crane fly larvae from February - to mid May. Search in areas shaded or wet areas, or where lawn health is poor, yellowing or missing. If there are no larvae, then search for the real cause of the poor lawn health.

In August, when the adults emerge, the leathery, shiny pupa cases (leatherjackets) are an indicator of where crane fly larvae were living and where the next eggs are most likely to hatch.

The adults mate almost immediately after they emerge. The females lay most of their eggs before they make their first flights and that's why they can build up rapidly in one area. Once they are airborne, there is no reason to try to control them.

What do I look for?

That's pretty easy. Just go out and look. The larvae are in the top three inches of sod, so just dig up a bit of sod and look through the roots and thatch for the blunt-ended, greyish-brown larvae.

How do I determine if I have a problem population of crane flies?

Even though that handful looks like a lot of crane fly larvae, it takes way more than this to do significant damage. The young larvae (above right) were picked up off the turf on a wet rainy day in February. They were just lounging around leisurely nibbling the grass. Dr. Gwen Stahnke at WSU Puyallup, says she's seen a healthy turf on good soil suffer NO significant damage from as many as 80 larvae per square foot. (Yes, she counted them all!). On the other hand, on poor soil with unhealthy grass, only 12 larvae have caused damage. Obviously, the key here is to start growing healthy grass that will not be severely damaged by a few crane flies. Please visit Crane Fly Management.

How many is too many?

The turf and entomology experts at Oregon State University and Washington State University have established the guidelines below through research and experience. Turf people have pretty high standards for commercial turf and golf courses, so if they are comfortable with these numbers, we can relax in the assurance that it will serve as accurate guidelines for home lawns.
Average number of crane flies per foot2 Your Decision
0 to 25 Do nothing; fertilize appropriately. May need to treat if turf is young, not well established or with poor root structure.
25 to 50 If your lawn is vigorous and healthy, do nothing. Decisions are based on the health of the turf, your personal tolerance, location and use of the turf
50 to 80 Treat crane fly problem. Look towards long-term solutions, such as replacing problem areas with a turf alternative species.
Make sure that the pesticides will not run downhill to streets where they can move to storm drains and on to streams. Birds, small mammals or pets may eat the dead contaminated larvae that come to the surface. So if the damage is not severe hold off.

What about that other crane fly?

THE COMMON CRANE FLY, Tipula oleraceae.

This is a new species similar to European crane fly. It is new to the area and it is not clear yet what implications will be for lawn management. So far, the turf specialists are not seeing damage in summer from this crane fly. For now growing healthy turf is the key for both crane flies. If you find crane fly life stages, at odd times of the year it may be this new species. If so, check the web page. By then we should have new information available.

Where do I get information on pesticides if I do have a problem?

WSU Hortsense has current pesticide information for crane fly management. To grow a better lawn or prepare for a new lawn, see the WSU Home Lawns Bulletin.

"Good turf culture and common sense may be the best weapons we have to control crane fly."
-Dr. Tom Cook, Oregon State University Turf Specialist
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