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 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.
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.