Fleeceworms

GAINES W. EDDY AND R. C. BUSHLAND.

SEVERAL kinds of maggots may attack the fleece of sheep and goats, infest old wounds, or be primary invaders of fresh wounds of animals.

The black blowfly (Phormia regina), the secondary screwworm fly (Callitroga macellaria), and the green-bottle fly (Phoenicia sericata) are the main species. They usually breed in large numbers In carrion.

The black blowfly is blackish green and about the size of the screwworm fly. It lays 50 to 100 or more yellowish eggs in a heap, quite different from the neat, white mass deposited by the screwworm.

The egg masses of all three blowflies look much alike. In infestations on sheep and goats they usually are deposited on soiled fleece. The larvae are creamy - white. The larvae do not usually feed as a colony, but may do so, especially in wounds of dehorned cattle. The life cycle takes about 2 weeks.

The black blowfly occurs in many parts of the world and in almost every State in the United States. It likes the cool weather of spring and fall. In midwinter and hot summer it becomes scarce.

Most of the infestations in sheep occur during the early spring when the wool gets soiled by feces, urine, or rain.

Usually only one or two animals in a group become infested at the same time, but an entire flock may be attacked when conditions are right. The flies also lay eggs on old wounds or wounds that are infested with screw-worms. The wool below the wounds infested with the screwworms is usually soiled or covered with matter and is attractive to the black blowfly.

THE SECONDARY SCREWWORM FLY resembles the screwworm fly in general appearance and color but is slightly smaller.

The eggs of the secondary screwworm fly are yellowish and are deposited in loosely cemented masses that contain few to several hundred eggs. The larvae are grayish. The life cycle is completed in about 10 days.

The secondary screwworm fly has been found in most of the States. It seldom becomes abundant in the North, but breeds the year around in Texas, Florida, and Arizona, and probably in southern California. Usually the black blowfly has just about disappeared by the time the secondary screwworm fly becomes abundant.

Livestock losses attributed to the secondary screwworm fly probably equal those caused by the black blowfly, because the fly is usually present in greater numbers and during the period when the screwworm fly occurs. It is most important in the areas where the screwworm fly abounds. It not only acts as a secondary invader by getting into wounds infested with screwworms; it also has the bad habit of leaving the wounds and infesting the fleece of sheep and goats. In such cases the death of the animal is almost certain unless the larvae are killed. The secondary screwworm fly is also a primary invader of fresh wounds.

THE GREEN-BOTTLE FLY is metallic green. It is about as large as the secondary screwworm fly. The pale-yellow eggs ordinarily hatch in less than 24 hours. They are laid on or around wounds and on the soiled fleece of sheep and goats. The larvae are deep cream in color with a slight purplish or pinkish tinge. Eggs develop into adults usually in less than 2 weeks.

The green-bottle fly has been found in almost every State. It is more prevalent in the South than in the North.

In importance to the stockman, the green-bottle fly does not rank with the other blowflies. Although the fly normally lives on dead or decaying matter, it may turn parasitic and attack livestock, especially sheep. Many cases in Texas, New Mexico, and Arizona are caused by the green-bottle fly. In Arizona it is especially bad. It may attack newborn lambs even before they are dry. It is active throughout the year in many parts of the South.

THE CONTROL of fleeceworms is difficult under many conditions, but good ranch practices and the use of an approved insecticide can cut livestock losses sharply.

The stockman's aim is to reduce the number of cases. Sheep should be sheared, if possible, before the flies become numerous. If that cannot be done, the animals should be watched closely for signs of infestations. Tagging, or shearing the wool from the crotch area, is used as a preventative measure by many ranchers, especially in the Southwest.

Insecticide sprays applied to the crotch and the tail prevent attack by fleeceworms.

Toxaphene is highly effective. Benzene hexachloride and chlordane are very good as preventives. Other chlorinated insecticides, such as DDT and TDE, are less effective.

Toxaphene is best applied as a 2-percent spray to the tail and the crotch.

area. The animals should be treated early in the season or before the flies become too active. A single spraying should carry the animals through the critical period.

A green-bottle blowfly, a closely related species, has caused heavy damage to sheep in Australia. Best results have been obtained there with benzene hexachloride at 0.5-1.0 percent (gamma isomer) and DDT at 1.0 percent.

Infestations of fleeceworms can be effectively controlled with the screw-worm preparation, EQ-335. For use against fleeceworms, the material is diluted 1 part to 9 parts of water. The infested area and about 3 inches outside the infestation should be encircled with the material. If the infested area is not too large, a very light dressing of the material in the undiluted form works well. It should be used with care, because the lindane in it (3 percent) is highly toxic to animals. It is not necessary to remove the fleece when EQ-335 is used.

GAINES W. EDDY, a graduate of Oklahoma Agricultural and Mechanical College, heads the Department's laboratory in Corvallis, Oreg. He has done extensive research on the control of lice, mites, and other arthropods that affect the health of man.

R. C. BUSHLAND became head of the Kerrville, Tex., laboratory of the Entomology Research Branch in 1952. He is a graduate of South Dakota State College and Kansas State College.