Best Way to Manage Crane Flies Is to Ignore Them

Todd Murray is the Whatcom County Integrated Pest Management Program Manager with WSU Cooperative Extension. He has a master’s degree in entomology from WSU.

Wondering what to do about the flock of long-legged, gangly crane flies hovering around your porch light? Washington State University (WSU) scientists’ advice: Don’t do anything.

Earlier this year, a WSU Cooperative Extension study of 50 lawns in the Lake Whatcom watershed found that only five percent had enough crane fly larvae to potentially cause turf damage. Todd Murray, manager of the Integrated Pest Management Project at WSU Cooperative Extension—Whatcom County, said that most pesticide applications for crane fly in the watershed, and in the county as a whole, are probably unnecessary. “Judging by our study, crane fly doesn’t seem to be a problem for most lawns,” he said.

Todd’s secret weapon: “Adults are harmless; use a fly swatter if you want to get rid of them. It’s the larvae, or leatherjackets, that might damage your lawn, and the best time to look for and manage leatherjackets is in the spring.”

Chlorpyrifos (also known as dursban) and diazinon, two chemicals commonly used to control crane flies, have been detected in streams, rivers and lakes throughout Washington. The U.S. Environmental Protection Agency has determined that diazinon and chlorpyrifos in drinking water is primarily due to their use by homeowners. Preventing insecticides from entering Lake Whatcom is a priority for local government agencies.

WSU Cooperative Extension—Whatcom County hosts a web site dedicated to crane fly management and research, http://whatcom.wsu.

edu/cranefly. The site has tips and strategies for homeowners, in addition to serving as a forum for researchers throughout the Pacific Northwest to share information.

Adult crane flies don’t do damage to lawns; it’s the larvae, or leatherjackets, that nibble at grass rootcrowns, which sometimes causes sparse patches in turf. Adult crane flies emerge from late August through September, mating and laying eggs in grass within 24 hours after emerging.

The eggs hatch into small, grayish-brown, worm-like larvae called leatherjackets. Leatherjackets feed on grass and clover in the fall, go dormant during winter, and start up again in the spring. Leatherjackets stop feeding (and doing lawn damage) about mid-May.

Spring 2001, WSU Master Gardeners sampled lawns throughout the Lake Whatcom watershed for crane fly larvae, with the following results:

•Lawns are considered to have a crane fly problem if over 25 larvae are detected. However, two WSU researchers, entomologist Art Antonelli and turf scientist Gwen Stahnke, have seen well-maintained turf show no signs of crane fly damage even when larvae exceeded 40 per square foot.

•Western Washington homeowners spent an estimated $13 million on store-bought insecticides just for crane fly management. (1999 Entomology Project Report-WSDA PUB 034 (N/1/00))

•In 2000, the Environmental Protection Agency deemed the two insecticides most commonly recommended for crane fly control, diazinon and chlorpyrifos (also known as dursban and other trade names), to pose too much risk to human health for residential use. Their residential uses are being phased out over the next few years.

•In 1988, the EPA concluded that the use of diazinon in open areas poses a “widespread and continuous hazard” to birds. Bird kills associated with diazinon use have been reported in every area of the country and at all times of the year. (U.S. Public Health Service, 1995)

•In a 1999 Department of Ecology study, diazinon was detected in two stormwater drains in the Lake Whatcom watershed; chlorpyrifos was detected in one.

•In a 1995 study of small Puget Sound streams, the U.S. Geological Survey had the following findings:

•“In general, more pesticides were detected in urban streams than in agricultural streams.”

•”Urban use of pesticides (about 1.1 million pounds/year) was more than three times greater than agricultural use.”