Reducing the Risk of Blowfly
Changing weather patterns mean that the typical flystrike season is starting earlier in the year and lasting longer. The warm weather and recent rain have provided ideal conditions for blowfly strike. Blowfly strike is a major issue in the UK sheep population; it has been estimated that 80% of flocks will have at least one case annually. The condition is painful and distressing and can be fatal. The scale of the problem varies from year to year with numbers building more rapidly in warm and humid conditions.
The green bottle fly (lucilia sericata) is the main cause of blowfly strike in the UK. The female fly is attracted to animals by odour when searching for a suitable site to lay eggs. Animals which have dirty back ends, dirty or open fleeces, footrot or open wounds are more attractive to the fly. The female lays over 200 eggs at a time. The eggs laid in the wool, hatch after 12 hours, providing there is the humidity to do so, with the larvae feeding on the living tissue of the host animal for three days, before dropping the sheep. The smell produced by the feeding larvae attracts more flies to lay and increases the severity of the lesions.
Signs of Infestation
At first there may be a small area of discoloured fleece, and the sheep may be restless and agitated with the tail twitching if the hind quarters are affected.
In more advanced cases there will be larger areas of stained and damp wool. The animal will appear sick, have suffered weight loss from lack of grazing and may be separate from the rest of the flock. Affected animals can die quickly due to the toxins released by the larvae and septicaemia from secondary bacterial infection.
Prevention
Prioritising fly control now will help reduce the risk as warm, wet weather can accelerate fly emergence, and as the season progresses the fly population increases. Be alert to the risk of blowfly strike in your area. NADIS produce an alert throughout the season. It is vital to control blowfly in the early part of the season to reduce the build-up of blowfly population. If using preventative products, they should be applied just before problems are expected. Always remember to follow the datasheet instructions regarding where and how to apply the product. The correct application is vital to protect the animals.
As green bottle flies are attracted to dirty animals, worm control is a critical part of blowfly control. It is also essential to shear dags away before applying preventative products to get the best results. In the longer-term selecting animals with less wool cover over the tail and rump can reduce the risk of blowfly strike. To avoid flies being attracted to your animals, ensure that dead stock is lifted promptly and consider where possible to avoid grazing livestock near fly breeding sites such as overhanging trees.
The table below provides a summary of the active ingredients for prevention and treatment. For a full list of available products visit scops.org.uk.
Control of fly strike requires good management, in combination with preventative products.
Treatment
When dealing with an affected animal it is important to clip out the entire affected area to see the extent of the damage. Apply a product which is effective for treatment and not just prevention of blowfly strike. By careful to apply according to datasheet instructions and not overdose the animal. In many cases an injectable antibiotic should be considered to cover secondary bacterial infections, and non-steroidal anti-inflammatory injections can be used to reduce pain. If the case is severe then euthanasia should be considered on welfare grounds.
Environmental Contamination
All products listed can kill non-target insects and impact on ecosystems. It is important to avoid use on days where rain is forecast, as this can cause washing out of products and reduce the effectiveness of the treatment. Animals should be held away from watercourses until products have dried into the fleece. A minimum of one hour is required for products to dry.
On some farms it may be possible to use fly traps to reduce the fly population. Fly traps can also provide an indicator of the best time to apply products.
5 Top Tips
- Flies have a negative impact on animal welfare and finances from loss of productivity – ensure you are prepared for this year’s fly season.
- Minimise potential egg laying sites:
- Dagg and crutch dirty backends
- Implement worming strategies
- Treat wounds quickly e.g. horn falling off
- Treat footrot lesions promptly.
- Shear sheep prior to the high-risk period.
- Refer to the NADIS blowfly forecast designed to show predicted emergence. This will help to predict risk and time treatment.
- Contact your vet if you would like to discuss fly control for your herd/flock.
Marion Mcmillan, SRUC Veterinary Investigation Officer, Marion.Mcmillan@sac.co.uk
Unearthed is the exclusive SAC Consulting members' monthly newsletter. Unearthed offers insights and tips from our experts on what we think is in store for farming and crofting in the coming months in order to protect and enhance your business.
Posted by Unearthed News on 17/06/2025
