Crane Fly & Common Crane Fly
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
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
How do I determine if I have a problem population of
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
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.
number of crane flies per foot2
||Do nothing; fertilize appropriately.
May need to treat if turf is young, not well established
or with poor root structure.
||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
||Treat crane fly problem. Look towards
long-term solutions, such as replacing problem areas
with a turf
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
Where do I get information on pesticides if I do have
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