Crane Flies: Harmless Bugs with a Bad Rap
A leatherjacket: larva of the cranefly
The crane fly, often called "daddy long legs", is one of the most misunderstood flying insects. Since it resembles the mosquito and is frequently found indoors, it has gotten a bad reputation as a harmful pest. Actually, these flying bugs are often a nuisance, but they do not bite nor do they spread disease. These "daddy long legs" are not to be confused with the common cellar spiders nor the arachnid opilones referred to as "harvestmen."
There are two types which inhabit our homes and gardens: the European crane fly, Tipula paludosa and the common crane fly, Tipula oleracea. The two are visually the same except to the practiced eye of an entomologist. One distinct difference is the number of life cycles per year. Typically, the crane fly emerges as an adult in the late summer/early fall when it mates and lays eggs in the soil of turf grasses.The adults of Tipula oleracea also emerge again in the spring when temperatures are warm enough.
Crane flies as flying insects are harmless; however, in the larval stage, they can do damage to turf grass when populations are heavy. The leatherjacket, as the larva is known, does feed on the thatch and roots beneath our lawns where it helps with the decomposing of organic matter. Healthy lawns and environments that attract birds and wildlife can withstand this insect, but sometimes, with dense leatherjacket populations, lawns will exhibit unsightly brown spots with poor growth. How can you tell if you have a problem?
It's important to understand that brown spots can be caused by a number of things including insects, poor irrigation practices, and fungal diseases. It is necessary to diagnose the source of the problem before trying to fix it. The application of soil and turf insect killers and fungicides should be done as a last resort since these things will indiscriminately kill all insects and fungi under your lawn, including beneficial ones. Follow thse simples steps to check for a crane fly larvae problem:
1) Choose 3-4 areas in your lawn for sampling. Observing the places where birds or wildlife are feeding can help you to pick likely spots.
2) Measure an area approx 6"X6" and use a knife to remove a plug 3" thick.
3) First, look in the hole for larva, then examine the mass you've removed. Larva will usually be visible in the root and thatch area. Pull the clump apart lightly. If it is easy to tear, it's a good sign that larvae have been chewing on the roots.
4) Count all of the larva and multiply X 4 to determine the number per square foot.
5) Repeat these steps in the other 2-3 locations.
There are apt to be other larvae in your sod such as cutworms, beetle grubs, and sod webworms. Leatherjackets are distinctly legless.
If your lawn is healthy, and you've found between 25 to 40 per sq. ft., you really needn't worry about treatment. Birds, small mammals, frogs, and subterranean beetles help keep the populations under control. If you've counted 50-100 per sq. ft., you may want to treat the lawn. There are granular insecticides and those applied through a hose-end sprayer. Most contain imidacloprid or cyfluthrin and target these pests plus a host of other soil and turf insects including grubs, fleas, chinch bugs, mole crickets, ticks, and ants. As an organic alternative, there are beneficial nematodes which are available for home delivery through www.tiptopbio.com. or other suppliers in your area.
Healthy lawn care practice:
Mow your lawn regularly during the growing season and leave the lawn clippings to enrich the soil. Cutting more than 1/3 of the grass blade per mow can have a negative effect on your lawn.
Water deeply but less often. If you see wilting areas in intense summer heat, a supplemental spot watering is more effective. Check for productive water penetration by taking a core sample after a typical watering. Moist lawn areas will actually attract more crane flies to a potential breeding site as well as encourage brown spot and other fungal maladies.
Aerate your lawn in the spring and again in fall. De-thatch every 2-3 years to insure good water penetration and to stimulate growth.
Try to avoid pesticides which kill our bees such as cyfluthrin and neonicotinoids like imidicloprid . Consider attracting birds and wildlife instead or opt for organic controls. It may be a nuisance to find that raccoons and skunks have been grub-hunting in your lawn, but they are actually helping. Placing garden netting with lawn staples in these areas at night will dissuade them. They don't like to get their feet tangled in it.
Remember to look at the larger picture. We share our environment with many other things, and the beauty around us is a product of a collaborative effort. Take the time to understand the presence of "pests" before attempting to eliminate them. They are usually minor inconveniences of short duration such as the crane fly which doesn't deserve its bad rap!
© 2011 Catherine Tally
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