Awareness and prevention of flystrike in sheep
The blowfly season is lengthening alongside an earlier emergence of flies, largely due to changing weather patterns. The changing climate means that is it important that farmers stay vigilant as blowfly season becomes increasingly challenging. Recent wet weather followed by warmer, humid conditions will significantly increase the risk of strike.
Blowflies are one of the most widespread ectoparasites affecting all ages of sheep. This high prevalence means that nearly all flocks are at risk of blowfly strike and it is estimated that blowfly strike costs the UK sheep industry millions of pounds each year.
Control of fly strike requires good management, in combination with preventative products as by the time that strike is visible, animal welfare and performance are already comprised.
Blowfly life cycle
The blowfly overwinters in the soil as a pupa, until soil temperatures reach 9-10°C when the pupa emerges as an adult fly, and then lay eggs on their host e.g. a lamb with a dirty backside. Adult females lay eggs in batches of up to ~200 eggs at a time. These eggs then hatch after 12 hours and live on the host for up to three days feeding as maggots rapidly damaging the skin and underlying tissue before crawling away and dropping off the sheep and pupating in the soil. When a sheep has multiple infestations e.g. numerous flies laying eggs, a wound is quickly created, and the odour is attractive to other flies.
Typical blowfly season is from spring to autumn; however, changing weather patterns and rising temperatures has resulted in some areas reporting blowfly strike beginning in March and lasting through to November.
The Impact of flystrike
Blowfly strike is detrimental to the welfare of ewes and lambs as well as being a major economic concern for farmers. Flystrike results in reduced productivity, lower fertility and weight gain. Lamb growth rates are reduced resulting in longer finishing times resulting in lambs being kept on farm for longer, increasing competition for grazing and grass for ewes. Ewe body condition is affected with weight loss following flystrike contributing in a delay to in ewes reaching target body condition for tupping. Loss of body condition also has the potential to impact fertility.
Managing and preventing flystrike
Prevention is key to enabling better control and flock protection therefore it is important to reduce the opportunity for flies to lay their eggs.
- Flock health - Implement a worming strategy to reduce dirty backends and soiled dirty fleeces which are attractive to flies. Also ensure that foot infections e.g. footrot and wounds from damaged horns are treated.
- Fleece management – Ensure timely clipping of ewes and any wounds from clipping have been treated.
- Deadstock management – Carcasses attract flies. Ensure that deadstock is removed promptly and covered before collection.
- Preventative Treatments – Use a preventative pour-on early in the season. Treating early to prevent flies from the first generation multiplying helps to reduce the risk as the season progresses.
- Monitor Blowfly Emergence – The SCOPS Blowfly Emergence Forecast can help to predict when blowfly emergence can be expected. Actual timing will vary across farms however the forecast can help identify risk periods. Currently the forecast now indicates full emergence across Scotland.
The potential for rapid escalation in fly numbers as numbers are about to reach their peak, alongside our changing climate means that extended blowfly management and protection is needed across flocks.
Five take home messages
- Blowfly strike affects sheep of all ages.
- Blowfly strike is common and changing weather patterns mean that is it important to remain vigilant to the risk throughout the year.
- Lamb growth rates and ewe condition and subsequent fertility are all negatively impacted by flystrike.
- Preventative treatment of ewes and lambs is required combined with good flock management to protect against flystrike.
- Protection is becoming increasingly challenging however the SCOPS Blowfly Emergence Forecast is great tool to help predict emergence.
Jamie Houstoun, Agricultural Consultant, Jamie.Houstoun@sac.co.uk
Posted by SAC Conulting on 21/07/2026
