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 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 1" 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.
Their dramatic 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 of cranefly.
Adult cranefly emerge from lawns in mid-August to late September, mate, lay eggs in the soil, and die in a few days.These eggs hatch in the fall to produce gray-brown worm-like larvae which develop a tough skin (hence the common name “leatherjackets”) and live in the upper 1" - 1.5" of the soil.
Cranefly eggs are laid in the upper 0.75" - 1.5" of the soil and are black and oval in shape about 0.03" long. The pupa is formed inside the last instar cuticle and is called a puparium.
Larvae feed on grass roots and root crowns, and are heavily preyed upon by birds, such as robins and starlings, in both fall and spring. The larvae go dormant in the soil through the winter (though in mild winters they may stay active through January). The greyish brown, inch-long larvae begin to feed heavily again in late February or March through April During the day they feed on roots within 1.5" of the surface, while on moist nights or wet, cloudy days they feed closer to the surface or emerge to feed on root crowns. They stop feeding in May and are inactive in the soil until they emerge as adults in August. Crane fly damage usually becomes noticeable in May or June (after feeding has stopped) as a sparse or brown patchy lawn.
Vigorous lawns are rarely heavily damaged by crane fly larvae, and recover more quickly. Crane fly eggs, laid in August and September, will die immediately if the soil around them dries. Water infrequently in late summer and make sure that the upper 2" of soil dries out completely between waterings; or stop irrigation altogether, especially if crane fly adults are seen on the lawn. Crane fly damage seems to be worst on lawns where the soil stays saturated through the winter, perhaps because the wet soil protects them from cold desiccation (drying out).