Crane Flies

Adult crane flies emerge from the soil beneath turfgrass, pastures and other grassy areas in late summer and fall. The adults have very long legs and resemble large mosquitoes. Females mate and lay eggs in grass within 24 hours of emerging. Eggs hatch into small, brown, wormlike larvae that have very tough skin and are commonly referred to as "leatherjackets". The leatherjackets feed on the roots and crowns of clover and grass plants during the fall. They spend the winter as larvae in the soil; when the weather warms in spring, they resume feeding. During the day larvae mostly stay underground, but on damp, warm nights they come to the surface to feed on the aboveground parts of many plants. When mature, the larvae are about about 1 to 1½ inch long. Around mid-May they enter a nonfeeding pupal stage and remain just below the soil surface. In late summer, pupae wriggle to the surface and the adults emerge. There is one generation a year.

In California, crane flies have primarily been found at damaging levels in the Humboldt and Del Norte counties and do not appear to be a problem on turfgrass in warmer, inland areas. All cool-season turfgrass species appear to be susceptible.

The larvae are the damaging stage of this pest. They feed on the roots, crowns, and aboveground portions of grass plants. Healthy, vigorous turfgrass can withstand low to moderate populations. Damage often becomes noticeable in March and April and appears as dying patches of turfgrass. Weeds may invade areas of dying turfgrass. Although the adults resemble mosquitoes, they do not bite or sting; it is believed that they feed primarily on plant nectar. Populations of crane fly larvae have been reduced by as much as 50% during the winter months and between March and May as a result of predators such as birds and predaceous ground beetles and other natural causes.

A vigorously growing, well-maintained turfgrass can easily recover from the feeding of crane fly larvae, even when the populations are fairly high. Monitor for crane fly larvae if the turfgrass is exhibiting areas of poor growth. Adequate nitrogen fertilizer is essential.

Drenches with the nematode Steinernema feltiae may give up to 50% reduction if properly applied.

Proper fertilization and irrigation are important factors in determining how much feeding by crane fly larvae the turfgrass can tolerate. Well-maintained turfgrass has been observed to withstand populations of crane fly larvae that averaged 40 per square foot, whereas unthrifty turfgrass may exhibit damage with as few as 15 larvae per square foot. Application of nitrogen in the spring may reduce damage. Provide better drainage for chronically wet areas and reduce irrigation. Craneflies thrive in wet soils.

Growing turfgrass species that require full sun in shady areas can reduce plant vigor and promote survival of crane fly larvae. In areas of low sun, consider a turfgrass species that prefers shade or a groundcover.

Remove excess thatch; it provides an ideal habitat for crane fly larvae, which feed mostly just below the thatch. Aerify the soil to stimulate root development and improve the movement of water and nutrients into the soil. Reseed bare areas of turfgrass so that weeds do not invade.

Monitor crane fly larvae in spring when the weather has warmed, generally in March. Samples can either be taken with a 4-inch diameter cup cutter or by digging up a 6" by 6" area of turfgrass about 1 to 2 inches deep. Larvae will usually be found at the base of the vegetative layer (thatch) or in the soil just beneath the plants. Pull apart the samples and count the number of crane fly larvae. If a 4-inch diameter cup cutter is used, multiply the number of larvae in each core by 11.5 to get the number of larvae per square foot. If a 6" X 6" area is sampled, multiply the number of larvae by 4 to get the number of larvae per square foot. Sample three or four locations and determine the average number of larvae per square foot. If damaged areas of turfgrass are sampled, take the sample from the edge of damaged area and not from bare patches, where the larvae would no longer be present. Continue monitoring through April, if no damage is observed by then, no further action is needed.

Research has not been conducted in California on treatment thresholds, but in Washington, the treatment threshold is 25 to 50 larvae per square foot.