Sheep Bot Flies
Oestrus ovis Linnaeus, Oestridae, DIPTERA


Adult -- The sheep nose bot is a hairy, yellowish, bee-like fly about the size of a common horse fly. Adults are 12-14 mm in length but are rarely seen.

Egg -- Within female fly.

Larva -- When fully grown, larvae are 20 to 30 mm long.

Pupa -- Pupae are found in the soil.


Distribution -- Sheep bot flies are found throughout the continental United States.

Hosts -- Sheep bot flies use sheep and goats as hosts.

Damage -- In parasitized animals, there is a purulent discharge from the nostrils, shaking of the head, gritting of the teeth, and possible loss of appetite.

Life History -- The adult female fly is active during summer and early fall. Eggs are retained in the body until they hatch. Flies deposit as many as 500 larvae in the nostrils of sheep. The larvae then move up the nasal passages to the nasal and frontal sinuses. The larvae remain in the sinuses for 8 to 10 months and then are sneezed out of the nostrils. The larvae pupate in the soil with the pupal period lasting 3 or more weeks, depending on temperature. Adults then emerge from the pupae and may live as long as 28 days.


Unfortunately, no practical means of control are available for the sheep bot fly.