The Adult European Crane Fly, also known as a “skeeter-eater” or a “mosquito hawk”, looks a lot like a giant mosquito. But they don’t bite people and don’t even prey on anything once they reach the adult stage of life. It is the larvae form of crane flies that creates all the trouble. The larvae, also known as “leatherjackets”, are major lawn and garden pests that feed just below the surface, destroying plant roots and stems.
Across the globe, there are over 15,000 species of crane fly. The adult female deposits eggs in clusters or groups (200 to 500 eggs per adult female) and adults can be found in areas that include marine, brackish and fresh water, which highlights the versatility of the crane fly. The crane fly larvae, also known as leatherjackets, hatches in about 2 weeks after deposited on the soil, look sort of like a fat brown silkworm (or a microscopic version of the creature from the movie Tremors), and mostly stay underground. These grubs destroy grass and turf. Eggs are long, rounded and a dark brown to black in color.
During mid to late summer, within a day of emerging from pupating, the adult female deposits her eggs, which are already fertilized, in the grass found in lawns, pastures, golf courses and other field locations. The larvae dine on grass and clover, as well as plant and grass roots – this destructive consumption of roots can lead to plant and crop death.
When winter comes, the larvae will overwinter and then continue feeding in the spring, causing visible damage to lawns and turf. The larvae will feed until the middle of May and then do not feed as they enter the soil to pupate, usually during summer (July to August). At the end of summer, the crane fly larvae will navigate to the top of the soil and emerge as adult European crane flies. The leatherjackets may survive for over a year before becoming adults, all the while wreaking havoc on lawns and gardens.
Signs of Damage
For leatherjackets, your lawn is at risk and may look “eaten” in parts. With this kind of infestation, you are likely to find uneven sections of grass that have been completely devoured, leaving only brown soil. Once a leatherjacket infestation gets extensive enough, holes may appear in your lawn overnight. These excavations are caused by skunks and other grub-loving predators as they search for crane fly larvae and other grubs. In addition, affected grasses may appear yellowed and unhealthy since they’re only receiving limited nutrients.
Check for crane fly infestation in spring by digging up a patch of lawn about 12 inches square and 2 inches deep. Count the number of leatherjackets. If there are more than 25, you’ll need to do something. With less than 25, the grass can usually outgrow the them.
Healthy lawns are less susceptible to crane fly infestations. Thatch if needed, aerate once a year, and add Calpril lime in spring and fall. Fertilize two to three times during the growing season. Irrigate deeply but infrequently, 1 inch to 1 1/2 inches a week, during dry months. Cut off water in September so the eggs will dry up.
A method of controlling adult crane flies is the application of insecticidal soap and pyrethrins. This method of adult crane fly control can be used safely if directions on the product are carefully followed. Sprays with pyrethrins will paralyze the crane flies and result in their death.
For leatherjackets, use a grub killer for lawn and turf to stop the crane fly infestation at the source: the soil, which is where leatherjackets live and feed. They will also target vegetables and flowers, killing the plants from the ground up.
Insecticidal soap & pyrethrin should be applied as soon as crane flies are discovered. Spray it as a contact killer. Use in accordance with directions on the product label.
Grub killer for lawns can be applied directly to your lawn and should be used at the first sign of grub damage. Use according to directions on the product label. Wilco recommends Spectracide Triazicide Granule that kills and repels a variety of destructive insects above and below ground and once the treated area has been watered and is dry, children and pets can return to lawn.
When to Use Control Methods
Early Fall (about 2 weeks after eggs have been laid), and early spring (once the ground warms up) are the most effective times to use control methods as these are the most active times for crane fly larvae. In the Fall, watch for the appearance of adult crane flies on your lawn and other areas around your property. When you start to see adults, eggs will begin hatching and feeding in about 2 weeks. If you are seeing active adult crane flies, then it’s time to apply control methods. Repeat those methods in early spring (March-April).