With warmer weather of late, coupled with recent rainfall, incidences of blowfly strike are being reported more frequently.

Blowflies are an external parasite that commonly appear over the summer months, however it is not uncommon to hear cases as early as April and as late as November.

In late-spring coming into the summer months, the population of flies increases rapidly. Couple this with the onset of warm, humid weather and rainfall, and you get the main contributing factors for the onset of flystrike.

Sheep that have a soiled fleece are most at risk of being struck down with flystrike. Thus, dagging/crutching dirty sheep will go a long way in reducing the risk of blowfly strike in the short term.

The most common area that sheep are affected is around the tail or rump region. However, they can also become infected on the shoulder, along the back or where a cut has occurred on the skin.

Blowfly strike occurs when flies become attracted by a foul-smelling, soiled fleece, and deposit many hundreds of eggs onto affected sheep. These eggs will then hatch into larvae and begin to feed on the sheep’s skin – causing wounds.

Within a matter of days, if action is not taken, it will spread; more and more sheep will become infected.


Obvious symptoms in sheep that have been affected with flystrike include: Foot-stamping; vigorous shaking; gnawing or rubbing of the tail; restlessness; wool loss; and loss of body condition.

Early treatment before the population of flies increases substantially will give farmers the best chance of controlling an outbreak.

The good news is that farmers have options when it comes to controlling and preventing an outbreak of flystrike.

Shearing ewes at this time will protect them over the coming months or some may opt for plunge-dipping either; pour-on products would be the preferred choice of product by farmers when treating lambs for the parasite.

Choosing a pour-on solution

It’s important to note that there are significant differences with pour-ons, with some only providing protection against certain parasites.

Furthermore, some products will treat and prevent against a parasite, while others will only prevent.

Both of these factors need to be taken into account when purchasing a product.

Pour-ons will provide protection against flystrike for up to about 10 weeks, however there are some products that provide protection for up to 19 weeks.

It is important to be mindful of the withdrawal periods associated with pour-on products; these can vary from seven to 40 days.

For farmers with ewes or lambs coming close to slaughter, it is essential that the withdrawal periods are adhered to.

Finally, care should be taken when using products to treat against flystrike. Protective clothing, gloves and a respiratory mask should be worn.

When treating for flystrike, it is important that farmers keep the following in mind:

  • Apply in dry weather;
  • Apply to clean, dry wool – crutch excessively dirty sheep;
  • Treat lambs early, before flystrike is anticipated;
  • Consider withdrawal periods when selecting a treatment;
  • When using a pour-on product, make sure to apply it from the neck down to the rump area.