Parasite Watch, Sheep farming


Flies are not only an annoyance to your flock; they also spread diseases and cost you money. Often most types of fly arrive at the same time every year, which means you could outsmart them. Find out which flies are prevalent when and how to best keep these pests under control.


Flies are common around sheep; they irritate the skin, some feed on a sheep’s blood and often spread diseases. If your flock is under attack from flies take action immediately utilising an effective fly killing product.

Which flies affect sheep and when?

This is when each of the most common types of fly reaches its peak:

Face Fly: June – targets the nose and eyes

Horn Fly: July – is a blood feeder

Horse Fly: August – is also a blood feeder feeds on their blood

Head Fly: August - feeds on sweat and secretions from the nose, eyes or udders

Stable Fly: End of September – a blood feeder, targeting the abdomen, legs and udders

Fly Timeline

What diseases do flies spread?

Horn and horse flies give particularly painful bites and stable flies can lead to blood loss. Yet as well as being a nuisance some flies commonly spread specific diseases. For example, head flies cause Black Cap in horned sheep and face flies transmit Pink Eye.

How do flies cost you money?

Sheep can become incredibly irritated by flies. In fact, they can become such an annoyance that growth is restricted and milk supply in females is reduced. This is less profitable for the farm, but you’ll also spend money on medical treatments to try and eradicate them.


Blowflies are especially problematic and a bad infestation can be fatal. Maggots are part of their lifecycle, so to check for blowfly maggots, part the wool over the tail to look for these. 

Adult blowflies lay eggs in sheep wool, which develop into maggots. Six days’ later pupae are in the soil and young adult blowflies emerge. In less than a week, the population of blowflies is already increased exponentially and an attempt to dampen the population growth is a significant challenge.

If blowflies lay eggs in sheep wool when there is already a wound (common from foot rot, other parasites, shearing cuts or heavily soiled fleeces etc.) the maggots invade this when they hatch. The larvae then excrete ammonia, which can lead to toxaemia, along with bacterial septicemia, creating a life threatening condition for the sheep.


Blowfly-Strike Prevention

Blowfly strike treatment

  • For the control of established blowfly strike use:

Fly & Lice Spot On

Dysect Sheep Pour-On


Plan of Attack

If you wait until fly populations are already established and then try to tackle them you’re unlikely to win the battle. It’s important to maintain a high level of farmstead hygiene all year round and form a plan of action in advance. Use fly traps, which can be made quickly and easily at home for free, plus medical treatments to keep flies at bay. Watch out for Parasite Watch notifications of fly populations from a farm near you.

Hone your strategy to fight flies and sheep will be far more content and productive without the disturbance.

DYSECT SHEEP POUR-ON 12.5 G/L POUR-ON SOLUTION contains alphacypermethrin. POM-VPS .FLY & LICE SPOT ON contains deltamethrin. POM-VPS. For further information, please see the product’s SPC or contact Zoetis UK Limited, Walton Oaks, Dorking Road, Tadworth, Surrey KT20 7NS. Customer Support: 0845 300 8034. Use medicines responsibly ( Date of preparation: August 2016