Blowfly strike in sheep

Blowfly strike is a serious disease affecting sheep of all ages, caused by the larvae (maggots) of the Lucilia sericata greenbottle fly – or blowfly – attacking the flesh of the sheep.

Preventative treatment of ewes and lambs is always the most cost-effective strategy against blowfly strike¹. It is vital to regularly check the Blowfly Risk Forecast to check the level of risk in your area, and the Blowfly Tracker to see how many strikes have been reported in your area - and report a strike if you see one.


: Blowfly strike is usually an issue from spring through to autumn, depending on the weather patterns.
The blowfly overwinters in the soil as a pupa, until soil temperatures reach 9°C when the pupa emerges as an adult fly. Each adult female produces over a thousand eggs, which are deposited onto sheep in multiple batches of around 200 at a time. The first stage larvae released from the eggs are small (about the size of a grain of rice) and cause no damage. However, the second and third stage larvae will rapidly damage the skin and underlying tissues, with severe damage occurring in as little as 24-36hrs after eggs are laid².
The first few flies that emerge in the spring can quickly give rise to many millions more, and as the whole lifecycle of the blowfly takes only 2-4 weeks, the risk to sheep increases rapidly through the summer as the fly numbers increase.
: Blowfly strike causes major issues to sheep farmers, and despite greater awareness, many still underestimate the risks of blowfly strike:

Welfare and productivity issues to sheep as the maggots literally eat the sheep alive.
Unpredictable blowfly seasons: One of the hardest challenges for blowfly control is predicting the start of the season each year as it can fluctuate considerably. This has been driven by changing weather patterns over the last decade, creating an increasingly unpredictable and lengthening season.
Financial consequences: the true cost of strike goes beyond treatment and is widely misunderstood. Despite the choice of products available for both treating and preventing blowfly strike, 94% of farmers3 say they have been caught out by a case of blowfly strike. Nationally, this inflicts a considerable cost on the industry every year, with the cost per flock estimated at over £1000 for a 250 ewe flock in an “average fly year”²
“The challenge for the industry is to understand the real specific impact of blowfly strike – that blowfly strike is not an inevitable part of farming and can be mostly avoided with the right management strategy” says Kate Heller, MRCVS, Technical Vet at Elanco. “There are no guarantees when it comes to blowfly strike – with significant levels identified into November, an essential part of any strategy, has to ensure an early treatment that extends right through the long season.”

Controlling blowfly strike in sheep

Being prepared means farmers can take control of this devastating disease by planning their time and resources to suit their farm, to the benefit of the health and welfare of the flock.

: Blowflies are attracted to lay their eggs on areas of soiling or damage (wounds) on the animal, or on carcasses. Therefore, the key to blowfly control is to minimise breeding opportunities by:
managing deadstock: remove deadstock as quickly as possible, and keep deadstock covered while waiting for collection
managing flock health: minimise faecal soiling through good worm control and fleece management, and through treating wounds, including foot infections
using a preventative treatment early in the season: prevent established blowfly strike in the flock to protect the sheep and to prevent those first waves of flies from breeding. Doing this will massively reduce blowfly numbers, and strike risk, later in the season.
treating struck animals: to kill adult blowflies and larvae.
Regularly check the Blowfly Risk Forecast, to check the level of risk in your area, and the Blowfly Tracker to see how many strikes have been reported in your area - and report a strike if you see one.
: Insect Growth Regulators (IGRs) are used to prevent blowfly strike becoming established. These products are not insecticidal, and instead work by preventing the harmless first stage blowfly larvae developing into the damaging second and third stage maggots that are responsible for flystrike.
The Elanco CLiK™ portfolio, made up of CLiK™ EXTRA, CLiK™ and CLiKZiN™ are IGRs that break the blowfly life cycle before the damage occurs:
: Select which CLiK™ product is best for your blowfly strike strategy:

These are the only products to benefit from FleeceBind™ technology that allows the product to spread and bind to give full fleece protection***, minimising the risk of flystrike.
Duration of cover depends on the correct application. Apply the CLiK portfolio of products to clean sheep, using the 4 stroke application method:
Best results will be achieved by holding the gun approximately 45cm from the sheep during application. Care must be taken to prevent animals from rubbing and removing the product, as this will almost certainly reduce the duration of protection.
Watch the video on how to apply the CLiK products:
: Correct application of CLiK™ products is essential for optimal protection and prevention of blowfly strike. The animation here shows how to apply CLiK products using the four stroke technique:
: Organophosphates (OPs) and Synthetic Pyrethroids (SPs) are insecticidal - they kill adult and larval stages of the blowfly on contact. Crovect™ offers treatment and control options for blowfly as well as for ticks, biting lice and headflies.
: To treat blowfly strike with Crovect™, it is important to apply directly using the T bar nozzle only to the areas affected by strike. Ensure that all affected parts are treated.
Sheep may be treated off-shears or at any time of the year.
Crovect contains a blue dye to aid in identifying treated animals. The colour is temporary and will fade from the fleece within 48 hours of application.

How do you compare?

See how you compare with our downloadable PDF – also full of key information, industry discussion, and recommendations for protecting against blowfly.