What is Blowfly Strike?

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.

This fly 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 laid.

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.

Why is blowfly strike an issue?

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.


• 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 farmers¹ 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.


• 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. It is vital to regularly check reports and trackers such as the NADIS risk alert map and our own Blowfly Tracker , to gauge the risks to your own farm.

“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, 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.”

How do you compare to others in the industry? See how you compare with our downloadable PDF– also full of key information, industry discussion, and recommendations for protecting against blowfly.