The European crane fly, Tipula paludosa, is a pest which has become established in the Pacific Northwest especially in areas with a maritime climate. There are reports of it establishing in parts of Northern California, New York state and the Northeast as well. Although largely a turf and pasture pest, it has been found feeding on such hosts as annual and perennial flowers and several types of vegetables and small fruits.
The adult crane fly has very long legs and looks like a large mosquito with a body about an inch long, not including the legs. Homeowners are alarmed when thousands of these large flies gather on the sides of homes. The crane fly does not bite or sting; it does no damage to houses; but its numbers do excite homeowners.
The wing span may be 2" across. Adults are clumsy and weak fliers. They are often found resting on an outside wall of a house, under a porch or in a garage. They may gain entry to a house when a door or window is opened. However, crane flies are harmless. Adults are short lived and may feed on floral nectar or not at all. There are many species in North America, but only 2 pose potential problems for landscapers and turf care managers. Those are the European crane fly and its close relative sometimes referred to as the marsh or giant common crane fly.
The large mosquito like insects are harmless. It is their larva that causes the serious damage.
Crane Fly eggs are laid on the surface of the grass and hatch within 2 — 3 weeks. The eggs are black and oval in shape about 0.1 cm long. The larvae of the European crane fly are known as leatherjackets because of their thick skin. They are light gray or greenish brown with irregular black specks. Leatherjackets are cylindrical but taper slightly at both ends and are typically 3-4 cm at maturity. The pupa is formed inside the last instar cuticle and is called a puparium. The pupae are brown and spiny and are 3.3 cm in length.
In the fall the larvae feed on the roots and cause stress to the grass below and above ground. By winter, the larvae burrow themselves deep into the ground and do not feed. If the turf doesn't suffer damage in the fall, it could be harmed in the spring when the leatherjackets do the most feeding. By mid June the larvae are at their largest. They wiggle to the surface. It is then that they can easily be detected because of the empty "jackets" left behind. This jacket protrudes from the lawn and be easily spotted on low-mown turf.
The leatherjackets feed primarily on turf on home lawns, golf courses and sometimes pasture grasses. They feed during the day at or below the surface of the turf on root hairs, roots and crowns. On damp warm nights, they migrate to the surface of the turf and eat stems and grass blades. Damage to turf occurs in the spring. Damage can occur on golf greens from birds pecking out the leatherjackets from the greens.
Leatherjackets look different from native species in that it has a narrow dark-colored band along the leading edge of the wing next to the light colored band. Unlike some native species, there is no pigmented areas or patterns on the veins, cross-veins or the rest of the wing.
Damaged turf from the European Crane Fly looks like yellowing spots are bare patches similar to white grub damage. Mid-May is the time when leatherjackets are feeding the most. Birds are major predators to the leatherjackets and that in itself can be damaging to high maintenance turf areas.
The suggested thresholds is from 15 — 50 larvae per square foot. They thrive in moist soil conditions and don't like overly wet or overly dry conditions. This is a key to controlling and reducing populations. Manual removal is possible by raking the lawn at night when the larvae emerge. Preventative insecticides are best applied in late fall while larvae are still small and active near the the surface. Testing on new chemical and biological pesticides are being conducted to find a better solution to control this new threat.
In the past there were 2 pesticides for use to control European crane fly larvae. Dursban and diazinon are no longer registered for home lawn care. These insecticides are toxic to birds and documented bird kills from these products have been reported. They are also known to be toxic to fish.
Alternatives to Dursban and diazinon are limited. Alternatives include restricted use pesticides, which can only be applied by a certified applicator. There are some general use insecticides known to kill bees and other beneficial and non-target organisms, such as fish. Always be sure the crane fly larvae population exceeds 45 per square foot of turf before considering pesticide use, and do not use pesticides in late summer.