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How To Assess Fly Density on Poultry Farms

Rowan Burgess |

Effective fly management isn’t just about using chemical products, but understanding which species are present, the best methods to control them, and when.

No poultry farm on the planet is fly-free, and up to a point, flies are an occupational hazard. However, you can have too many, so the crucial question is, not do you have flies on your farm, but what is their density?

Monitoring fly density is part of suitable management protocols, and an essential element of any poultry farm fly control program to help keep insect density at acceptable levels. 

1. Identifying Common Fly Species on Poultry Farms

Many fly species are common to all farms, but there can be some variation depending on the type of livestock and the location. Identifying the species on your poultry farm is crucial to effective management protocols.


Bluebottles are among the easiest fly species to identify with their distinctive metallic blue/green sheen. 

Around 5-8mm long, bluebottles are a bit larger than the common housefly. Bluebottles have large red eyes and transparent wings with sharp, noisy flight.

Bluebottles live outside during the summer and shelter indoors during the winter for warmth and food. Animal faeces and general farm waste attract these flies and are also partial to animal remains!

Cluster Fly

Cluster flies are easiest to identify by their long wings, which overlap at rest which is not a feature of any other species.

Cluster flies are a dark grey colour with an olive/grey coloured thorax covered with minute golden-brown hairs. They also have patches of gold hair on their wings and back.

Cluster flies hibernate in animal housing during the winter and then live outdoors in spring and summer, where they lay their eggs. You can sometimes spot them high up in a barn or shed when it’s cold, attracted by a window or light.

Fruit Fly

Fruit flies are attracted to food and not just fruit – they love animal fodder, so feed storage and disposal on the farm must be very well managed.

Fruit flies are the smallest species around the farm, only 3mm in length. They have a grey-black abdomen underneath, and their core hangs down low when they fly, so they’re easy to spot.

These flies have transparent wings, large red eyes, and their thorax is tan or pale yellow.

Filter Fly

Filter flies are easy to identify because they have a feeble flight; they often look like they’re jumping or hopping rather than flying. Otherwise, they’re hard to see at only 2mm in size.

Filter flies love manure, animal dung, and organic matter, so they are hugely attracted to poultry farms. They’re a controllable species with good management practices and respond well to regular insecticide treatment and physical traps.


Houseflies don’t have teeth, so they only feed on liquids, but they can pulverise more solid foods into a liquid they can consume using their spongy mouthparts.

These flies are around 4mm-6mm long, grey, and have four distinct black stripes on their thorax. Their eyes are red, prominent, and large, as vision is integral to their ability to search for food.

There are lots of potential food sources on the farm to attract them, including manure and animal feed.

2. Determining the Fly Density Threshold for Your Farm

What Is Fly Density?

Fly density is the level of flies present on the poultry farm at a specific point in time. 

Density inspections should be a regular part of routine monitoring to assess the effectiveness of control systems and spot any new problems. One-off inspections are less helpful in establishing number trends.

The density threshold is when the fly population is within acceptable levels and control measures are effective. 

Fly management is an essential part of complying with an environmental permit. Intensive poultry farms of a specific size and capacity require an Environmental Permit.

Factors To Consider When Determining Fly Density Threshold

  • Regular inspections are essential to building up an informed picture of insect populations
  • Each species will have a different recommended density threshold
  • Depending on the species, the density threshold may be appropriate for the adult insect or the larval stage, larval, or both. Monitoring flies throughout their entire lifecycle allows normal levels to be established
  • Monitoring density on different parts of the farm will identify areas where breeding is taking place
  • You’ll never eliminate every fly, but keeping them under the recommended threshold will satisfy environmental permit requirements and should ensure the health of the flock

3. Conducting Fly Density Assessments

Carrying Out the Assessments

Fly density assessments must be done twice weekly during the primary insect season, April to October, and once weekly at other times of the year.

Each species may be assessed in a different location depending on its lifecycle and feeding habits. Use several monitoring locations and ensure they are always the same for consistent evaluation.

Recording and Analysing the Data

Data should be meticulously recorded with the date and time of day. It can also be helpful to note the weather type at the recording time, which might account for unusual fluctuations.

Any changes within the vicinity of the recording location which may impact fly density must also be captured, such as the re-siting or removal of a manure pile.

Precise data demonstrates whether management programs are working and keeping the fly population within the acceptable threshold. It can also highlight unusual trends which require further investigation.

Accurate data helps rebut complaints from neighbours. It demonstrates both adequate control measures and control fly populations, which may not correlate with the neighbour’s complaint, i.e., the source of the problem is elsewhere.

There is no set guidance or objective levels in the Clean Neighbourhoods and Environment Act 2005, so it’s usually a question of arguing the point with the complainant. Demonstrating good fly management programs is critical.

4. Implementing Fly Management Strategies

There are different types of fly management protocols, including the direct and obvious such as fly traps, smoke bombs, and insecticides. There are indirect methods like building design, manure management, and environmental adjustments. 

  • Fly Traps – good old-fashioned sticky paper, outdoor trap bags, and electric fly killers all do the job and are affordable and environmentally friendly.
  • Smoke Bombs – not so much a bomb as a smoulder; just light the wick, and the smoke fumes will infiltrate every nook and cranny in the building, ideal for empty poultry sheds.
  • Insecticides and Larvicides – for topical spraying of empty housing and breeding sites around the farm, most of these products have a long residual action which means they keep working for a defined period after spraying
  • Fly Sprays – handheld for small areas or buy a large concentrate that can be used around the farm to target specific problems

5. Evaluating Fly Management Strategies

Importance of Monitoring the Effectiveness of Fly Management Strategies

Accessible and well-recorded data demonstrates whether fly management strategies are working or not. Consistent monitoring helps apply products where they’re needed most, making the best use of time and money

Thorough tracking is essential to a fly control program and promotes farm and flock health, minimising disease and maximising productivity.

Making Adjustments to Your Fly Management Strategies

It’s essential to respond to changes in the data and adjust management strategies as circumstances dictate. Regular monitoring flags up problem areas before they become serious.

Final Thoughts

Effective fly control requires various measures, including strategic programs assessing insect density and targeting fly populations with appropriate control methods.

For a comprehensive range of fly control products to suit all types of poultry farms, consult Dalton's website.