Crane Fly Infestation

Written By: Stephanie Larson, PhD
Published: April 1, 2020

Crane flies, Tipula oleracea, have once again appeared on Sonoma and Marin County’s range, pasture and cultivated lands this season. I have seen their presence only 3 times during my career, but when in large numbers, the done significant damage. The seasonably warm, average 68 degrees, November, followed by a December that lack proper chilling days, resulting in the survival of excessive Crane fly larvae. Weather conditions have led to current infestations on range, pasture and cultivated lands. Larvae are usually killed when a hard frost occurs during the winter season. During this season, we did not experience an adequate frost to kill the larvae; resulting in a large larvae survival.

Crane flies, sometimes referred to mosquito hawks, lay their eggs pastures or cultivated lands (silage); these eggs hatch into small, brown, wormlike larvae that have very tough skin, sometimes referred to as” leatherjackets”.  The crane fly goes through a metamorphosis or changes body types during its lifecycle that lasts approximately one year. From the time the female lays her eggs until they reach adulthood, the fly changes from a larva to a pupa, then to an adult. Each cycle serves a specific purpose for growth and development of the crane fly. As larvae continue to feed on roots, crowns, and aboveground portions of plants, damage becomes more noticeable in March and April. The damage appears as large dying patches of grass (Figure 1).  

Larvae are consuming forage at an alarming rate. During the day larvae mostly stay underground but on damp, warm nights they come to the surface to feed above ground parts of many plants. The larvae vary in size, but at maturity are 1 to 1 ½ inches long. Producers are reporting many areas, completely denuded of forage. In areas affected, there 100% loss.  Around mid-May, larvae wriggle to the surface and the adults emerge; there is one generation a year. The larvae are the damaging stage of this pest (Figure2).


To determine if these patches are from larvae infestations, dig at the edge of bare ground and grass, 1-2 inches below the surface, larvae will usually be found at the base of the vegetative layer (thatch) or in the soil just beneath the plants. They will be anywhere from ½ to 1 inch in length.


Control options are limited, especially if the land is under organic production. Beneficial nematodes can be spread on the land to reduce the larvae infestations. Unfortunately, this method results in only 50% control. Organic sprays can also be used, but their efficacy has not be researched in California. Discing bare ground might expose larvae to predators such as birds and predaceous ground beetles and other natural causes. The use of chickens might also be effective if they are able to scratch the ground to get the larvae.

Bare patches of ground can be seeded if done early. Given it is so late in the growing season, reseeding with annual species, to prevent weed infestations or soil erosion, will be the best option. You can graze the silage crop in order to recoup forage losses.

Producers experiencing this damage may be eligible for assistance.

If you are under organic certification, contact your local certifier. They need to know that you are experiencing a forage loss emergency. All affected producers should contact the Farm Service Agency (FSA), 707-644-8593. FSA is taking applications for forage lost, through their Emergency Livestock Assistance Program (ELAP). To fill out an application, their office is located at 1301 Redwood Way, Petaluma.  Learn more at 

If you need additional assistance, field visit or support letter of loss from UCCE, please contact me, at or Randi Black,

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