Shore Fly

Shore fly (family Ephydridae) is a common problem in greenhouses and nurseries where there is algae, excess irrigation, and prolonged wet surfaces. The adult is a stout, dark gray fly about 1/12 inch (2 mm) long. Adults have short antennae and short legs and at rest they hold both wings overlapping the body. Adults' overall appearance at rest resembles the common fruit fly, except the body is darker and the large eyes are blackish. Each of the translucent gray wings has three pale spots, which appear to be five, pale blotches when the wings overlap at rest. Note that fungus gnats and moth flies can also be problems in overly wet conditions. Learn how to distinguish the adults and larvae of these from shore flies.

Females lay tiny, oblong eggs in algal scum where the larvae feed. Shore fly larvae have no distinct head capsule and the body is opaque yellow to whitish. The pale-colored larvae have a forked, breathing tube with fringed tips at the tail end that is held at the water surface. The elongate pupae also have a forked breathing tube and are initially pale but become dark brown as they age.

Shore flies can be especially abundant in frequently irrigated greenhouses and overly wet greenhouses. Numerous adults are a nuisance to workers and customers. Although neither adults or larvae feed on plants, the adults can be contaminated with spores of plant-pathogenic fungi and may spread these around growing areas. Dark specks of adult feces are deposited on plants, reducing aesthetic quality.

Shore flies become abundant due to overly wet environmental conditions and certain cultural practices. Properly manage algae, irrigation, and weeds to avoid problems with shore flies. Prevent growing-area surfaces from being wet for prolonged periods. Manage irrigation and drainage systems well to prevent drips and puddles. Treat to control algae. Pesticides alone are unlikely to solve a shore fly problem.

Biological control of shore flies has not been investigated.

Keep production areas free of algae and weeds. Especially prevent overwatering, standing water, and prolonged wet surfaces.

Cultural controls are organically acceptable management methods. Some formulations of the botanical pyrethrins without piperonyl butoxide (PyGanic) and spinosad (for adults: Naturalyte, Entrust SC) are organically acceptable.

Yellow sticky cards placed in greenhouses will capture adult shore flies especially when placed horizontally, although when abundant the activity of adult shore flies is obvious. See Monitoring with Sticky Traps and Sticky Trap Monitoring of Insect Pests for more information.

Because shore flies do not feed on plants, insecticide application may not be warranted unless other pests are also the target. Aerosols and foggers may be better at controlling adults than sprays, but for this pest proper cultural and environmental controls are the most effective practices.

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