This fact sheet was developed by students enrolled in Purdue's ANSC 442 Sheep Management course in Spring 1998, as a semester project. These fact sheets provide useful information on various topics related to sheep. View the list of fact sheets.

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External and Internal Parasites of Sheep

Samantha Starr
Erin Mengel
Troy Mason
Amy Compton

These are classified as external parasites. These are relatively easy to manage if you take care of the problem right away. Minor injuries are usually seen if taken care of properly. This will discuss some of the things that you can do if your sheep get lice or ticks. When in doubt, consult your veterinarian for more information.


Classified as arachnid parasites.

There are two types:

All are blood sucking.


Life Cycle

Egg 1-4wks

Adult Larva

1 Year Total

Nymph 1week

Female adult process: Engorge in blood, detach, and lay eggs.





Two types:

  1. Anoplura-Bloodsucking


                    Narrow head
                    Attacks mammals only
                    Flattened body

  1. Mallophaga-Biting


                    Larger head
                    Attacks birds and mammals
                    Flattened body

Transmitted by direct contact and purchased sheep that are infected.

Life Cycle

Female Hair egg

(molt) (hatch)

14-21days total Immature Adult



Build-up factors



Sheep Nose Bot Fly

Lay eggs around nose, larvae crawl inside nasal passages where they stay for a period of 2-3 months before they are all sneezed out or crawl out.  Cause animals to breathe in dust and make sheep more succeptible to bacterial infections of the respiratory tract. Cases of up to 4% weight loss have been documented. Can cause death in older sheep and sheep with severe infestation.


Blow Flies

Some types of blow flies, will lay eggs in the dirty wool of the sheep.  Usually these are laid in the groin area of in wounds. When the eggs hatch, the maggots feed on the surface of the skin all over the body. Maggot infested sheep stamp their feet, try to bite areas infected with maggots and become restless. Cause decreased performance. Same types of problems associated with houseflies, stableflies and face flies. Especially a problem with sheared sheep in the summer.



Biting gnats feed off of the blood of the sheep. Specific importance of C. variipennis transmits the virus which causes blue tongue.  Infected sheep have inflammations, swelling and hemorrhaging of the mucous membranes, mouth and intestines. Mortality rate for bluetongue is about 50%. Side effects are abortion and deformed lambs.