RUTGERS COOPERATIVE EXTENSION NEW JERSEY AGRICULTURAL EXPERIMENT STATION


Black Flies and their Biology

Black flies, commonly called buffalo or turkey gnats, are pests of man and animals in many areas of northwestern New Jersey. They are small dark flies that fly about the face, enter the eyes and ears and cause a burning sensation as they attempt to obtain a blood meal. Most species are 2 to 3 mm (1/8'') long; a few species reach lengths of 4 to 5 mm. Of more than 600 species of black flies, about 20 have been found in New Jersey.

Adult black flies are distinguished from other similar black flies by having 9, 10, or 11 segments to their antennas (most species have 11) and no simple eyes (ocelli). The second body region (thorax) is strongly convex, giving a humped appearance. An adult female black fly is shown in Fig.1. Only the female black fly bites. Male mouth- parts, adapted for plant feeding, cannot penetrate the skin of humans or animals.

All immature black fly stages (eggs, larvae, and pupae) require moving water for development since water movement provides their oxygen and food. Large populations can be found in most of the rivers and streams in the northern portion of the state. They are usually found in those parts of a stream with riffles, not quiet pools.

Seasonal Development

The time required for development from egg to adult depends on the species, water temperature, available food, and other factors. Females deposit from 150 to 500 eggs. Some species place them on submerged objects in the stream such as water plants, rocks, leaves, or twigs; others simply scatter the eggs over the water surface. Eggs will hatch in four or five days when the water temperature is 70 F. Eggs deposited in the fall will not hatch until the water warms in the following spring.

Larvae (Fig.2) attach themselves to submerged objects and molt six times, as they grow. They are easily distinguished from other aquatic immature insects in that they are elongate with the hind part of their bodies swollen. A head fan sweeps food material into the mouth. A single proleg on the thorax is used to hold onto a secreted silk thread. Spinning more thread allows the larva to migrate rapidly downstream. Rows of hooks at the hind part of the body enable attachment to submerged objects.

The larva spins a pupal case (Fig. 3) and changes to a pupal stage within it. In Fig. 3, the pupa is slightly removed from its case. The long branching tentacles are used for breathing.

Adults emerge from pupae in two to three days when water is warm and are capable of immediate flight and mating. Although their flight range is usually less than 10 miles, some may travel much farther from their place of origin. Some species of black flies do not feed as adults; others require a blood meal in order to produce eggs. Females live from a few days to more than three months. They prefer calm sunny days, and will not fly at night or on windy days.

Black flies are attracted to their animal or human blood meal host by the carbon dioxide and moisture present in exhaled breath, dark colors, convection currents, perspiration, perfumes a toiletries.

Economic Importance

Black Flies are annoying when numerous, even if they are not biting. They often fly into eyes, nose, ears and mouth. Bites cause pain and dermatitis at the site of the bite because black fly saliva is toxic. Intense itching may last several days; serious allergic reactions may occur.

Flies can discourage people from remaining in or visiting certain areas. Some recreational area in northwest New Jersey are not used to capacity because of black flies; tourists leave much earlier than they had originally planned.

Losses to livestock and poultry industries are difficult to evaluate, but there is usually a drop in milk, beef, and egg production where black flies are numerous. The flies are a source of irritation to livestock and cause accidental injury (in animals trying to avoid the flies), tougher beef, reduced reproductive capacity, and reduced resistance to disease.

Control

Repellents offer some relief against black flies, but the effect is usually only temporary. Success of any repellent depends on: individual human differences; the species of black fly present in the area; and the temperature, humidity or time of day. There are times flies will bite regardless of the repellent or concentration used.

Yard fogging for black flies is not recommended or effective control because it does not destroy the larval source of this pest; and black flies travel long distances and can reinvade previously treated areas.

Agencies controlling black flies have moved away from applying traditional insecticides to moving waters. They now recommend Bacillus thurgiensis israeliensis (B.t.i), an insecticide derived from naturally occurring soil bacteria that is safer for people and the environment. Treatment of streams with B.t.i. can provide control if intense environmental monitoring is used to time applications. States in our region have successfully used B.t.i. for many years.

Adapted from "Black Flies and their control", Stanley G. Green, Ph.D., Extension Urban Entomology, The Pennsylvania State University, Cooperative Extension Service. Edited by Wayne Crans, Ph.D., Department of Entomology, Rutgers, The State University of New Jersey.

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RUTGERS COOPERATIVE EXTENSION NJ AGRICULTURAL EXPERIMENT STATION RUTGERS, THE STATE UNIVERSITY OF NEW JERSEY NEW BRUNSWICK

Distributed in cooperation with U.S. Department of Agriculture in furtherance of the Acts of Congress of May 8 and June 30, 1914. Cooperative Extension work in agriculture, home economics, and 4- H. Zane Helsel, Director of Extension provides information and educational services to all people without regard to sex, race, color, national origin, disability or handicap or age. Rutgers Cooperative Extension is an Equal Opportunity Employer.

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