Sheep farming

DIY early warning of fly population explosion

By the time you notice cattle or sheep being troubled by flies, a population explosion is already taking place. However, it's easy and cheap to make some fly traps (Figure 1), and then keep an eye on them every few days for an early warning that fly numbers are on the rise. You need to choose suitable bait for the flies you wish to trap, for example offal, such as raw liver is suitable bait for the fly species that bother livestock.

DIY fly trap

Figure 1 – creating a DIY fly trap

DIY fly trap

Figure 2 – DIY fly trap

Of course, an early start to controlling insects around livestock gives the best chance of minimising the annual population explosion of flies and midges that begins as soon as average daytime temperatures reach 10°C (Figure 3).

fly population

Figure 3 – increase in population of different flies

Delaying the start of control measures can mean playing catch-up and usually losing, and also assuming that winter frosts - a rare thing anyway so far this winter - will help reduce the coming summer’s insect populations.

Even if air temperatures are below zero for several days running, the larvae of some species relevant to livestock typically over-winter about 10 centimetres below the soil surface where frost may not penetrate, so this cannot be relied upon to kill insect larvae.

Moreover, larvae of some species over-winter in woodland litter, where frost penetration is quite rare no matter how cold the weather. Then as soon as they hatch from pasture or woodland, blood-sucking species can migrate several kilometres to find livestock on which to feed.

While farmers cannot eliminate insect breeding sites from pasture and woodland, a meaningful impact around farm buildings is possible by minimising open dung heaps (Figure 4), slurry puddles, and old hay and straw stacks.

dung heap

Figure 4 - open dung heaps

For maximum control, action must start before the insect breeding season; waiting until insects are bothering livestock allows breeding populations to become established and difficult to get on top of.

In conjunction with good farmstead hygiene, residual pour-on pyrethroid treatments such as deltamethrin (e.g. Fly & Lice Spot On™) or alphacypermethrin (e.g. Dysect™ Cattle Pour-On 15g/l and Dysect™ Sheep Pour-On 12.5g/l) are licensed to control insects for up to eight weeks depending on species and population. In cattle a long acting cypermethrin (Flectron Fly TagsTM) is available giving season-long fly control from a single tag. Cattle and sheep producers should discuss insect control options with their vet or qualified animal health adviser.

Aided by home-made traps placed around your livestock areas, an early start to control measures can mean fewer treatments in total may be required, and therefore costs minimised. Financially, another upside may be available because fly nuisance on cattle has been shown to reduce milk yields by up to 0.5 litres/cow/day or growth rates by 0.3kg/head/day.

Research into the use of insecticides against the Culicoides midge species, known to be implicated in the transmission of several viruses including Bluetongue and Schmallenburg, found a deltamethrin-based pour on treatment to be an effective control method.2


  1. Jonsson et al (1999). Med. Vet. Entomology 13, p372-376.
  2. Mehlhorn et al (2009). Journal of Parasitology Research. Vol 104: p809–813.

Fly & Lice Spot On™ contains deltamethrin, POM-VPS. All Dysect™ brands contain alphacypermethrin, POM-VPS. Flectron Fly TagsTM contains cypermethrin (cis 50:trans 50). POM-VPS For further information please see the product SPC, or contact your veterinary surgeon, SQP or Zoetis UK Ltd, Walton Oaks, Dorking Road, Walton on the Hill, Tadworth, Surrey, KT20 7NS. Customer Support 0845 3008034. Always seek the advice of your medicines provider. Use medicines responsibly (