WOOL MAGGOTS (FLEECE WORMS)

 Wool maggots, the larvae of blow flies, live in wet, matted, and soiled wool around the rear of the animal and in wool surrounding wounds. The eggs are deposited in dirty wool or on wounds. After hatching, the maggots spread over the animal and feed on dead tissue under the fleece. Maggot-infested sheep become restless, stamp their feet, try to bite the irritated areas, and may leave the flock to hide in secluded places. The main species are metallic flies such as Phormia regina, Phormis cuprina, and Cochliomyia macellaria. Fatal secondary infections often follow wool maggot attacks.

LICE

Several species of sucking and chewing lice infest sheep and goats. They are not normally as prevalent as sheep keds, though, and are seldom a problem in flocks that are treated for keds. The African sheep louse, sheep foot louse, and sheep body louse all suck blood from the animals, while the sheep biting louse feeds on skin scales and wool fibers. Symptoms of lice include severe itching by the animal and rubbing on fences and other surfaces to relieve the irritation from the bites. Animals may rub and scratch until they denude areas of skin, and the wool of infested flocks becomes ragged and inferior in quality. Heavy louse populations cause anemia and make animals more susceptible to respiratory and other diseases. Lice are generally more of a problem in winter. Distribution and abundance of these species are not well known. Eggs are attached to the hairs but can hatch even after being dislodged from the animals for several weeks. Immature and adult lice can survive for a week off the host. The eggs of the sucking lice hatch in 10 to 18 days; those of the biting louse, in 5 to 10 days. Females can begin laying eggs about 2 weeks after hatching.

SHEEP KEDS (TICKS)

 Sheep keds, Melophagus ovinus, are primarily a pest of sheep, but occasionally are found on goats (Figure 1). The adult is actually a wingless fly resembling a tick in appearance. The adults are grayish-brown, sixlegged, and 1/4 inch long with a broad, leathery, somewhat flattened, unsegmented, saclike abdomen covered with short spiny hairs. Unlike true ticks, keds spend their entire life cycle on the animal; however, they can crawl readily from ewes to lambs. Sheep keds can live up to 6 months, during which time the female produces about 15 young at the rate of approximately one each week. Reproduction is continuous, though slow during the winter, producing several generations a year. Unlike most insects, the female sheep ked gives birth to living maggots, which are nourished within her body until they are fully grown. The maggots are 1/4 inch long, whitish, oval, and without legs. The skin turns brown within a few hours after birth and forms a hard puparium (case) around the larva. These cases are often called eggs, nits, or keds. Adult keds emerge from the pupal cases in 2 to 5 weeks, depending on temperature. They crawl over the skin and feed by inserting their sharp mouthparts into capillaries and sucking blood, much like a mosquito. This results in considerable irritation, which causes the animal to rub, bite, and scratch at the wool, thus reducing the amount and quality of the fleece. The feeding punctures also cause a condition known as “cockle” in tanned skins. Hide buyers downgrade sheep skins with cockle because it weakens and                               Figure 1. Illustration of the adult sheep ked.

discolors them. In addition, keds in large numbers can cause anemia, which can weaken the animal and make it more susceptible to other diseases.

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