FREE Delivery On All Orders Over £250 - Conditions Apply

Supplying the poultry industry for three decades

How To Monitor Adult Flies on Pig Farms

John Seo |

Flies on pig farms are an inevitability. The challenge for the pig farmer is keeping their numbers within acceptable levels.

Flies affect herd health, causing skin problems and irritation for pigs - while also being vectors for many serious diseases.

Fly control programmes are part of good farm management; an essential element is monitoring the adult fly population year-round.

Why Is Monitoring Adult Fly Activity on Pig Farms Necessary?

Flies affect the yield on pig farms and also carry and spread nasty diseases like Salmonella, E-coli and Porcine Reproductive and Respiratory Syndrome (PRRS).

Monitoring adult fly populations is necessary to assess the effectiveness of fly control methods. Surveillance also acts as a red flag for unexpected increases in numbers, which can indicate a specific problem.

Fly control is essential for stock health and welfare, so it must be proven to work. Routine assessments of adult fly numbers are part of proactive insect management and a necessary element of a rigorous control programme.

What Are the Benefits?

Accurate monitoring of the adult fly population around the pig farm supported by sound data recording will identify problem areas or unexpected rises, intensifying insect control.

One of the main benefits of recording the numbers of adult flies is that it establishes a baseline population, making it easier to identify changes. Operators can anticipate trends and hikes, allowing their fly control to be pre-emptive rather than reactive.

Comparing data over different months and years supports fly control measures' efficacy (or otherwise). It can highlight problems like chemical resistance or suggest a change in farm layout or design.

Matching records to specific times on the calendar helps rebuff complaints about infestations from properties near the pig farm. This data also demonstrates to Environmental Health Officers that the unit has a proper fly control programme. 

Monitoring Adult Flies on Pig Farms

There are several different methods of monitoring adult flies around the pig farm. Monitoring should be consistent regarding location and frequency to yield the best data. Here are some of the most suitable procedures for monitoring.

Indoor Resting Counts

The common and lesser house fly typically rests in groups on surfaces, so monitoring population numbers for this species is relatively easy.

For the most accurate data, outline an area of one metre by one-metre squares on the surface of internal walls at different points. The ideal height for precise monitoring and ease of recording is head height.

Squares should be away from areas of footfall or where vehicles are moving around. Resting flies are recorded within each square twice a week during the man fly season, through April to October, and once a week for the cooler months. Year-round monitoring is important for farm health!

Take care not to spray insecticide over these areas as chemical treatments have a long-lasting residual which affects data.

Adhesive Paper Traps

Adhesive paper traps are used in indoor pig units and are particularly effective at monitoring lesser housefly levels. Rolls hang at head height in areas where fly numbers proliferate.

Every week, detach a set amount of paper from the roll to count and record the number of flies - it's as simple as that! A fresh length of the same size is then pulled down and exposed, ready for the following week.

Open-air Scudders

A Scudder grid is a wooden slatted device put on the manure heap for a few seconds and then removed to yield a fly count. For accuracy, it's best to complete this test in warm conditions and when it's not windy.

Open-air Adhesive Paper Catchers

Post sticky paper traps around the farm for outdoor pig units and remove them after one week. Fly species can then be identified and recorded.

Because of environmental variables like wind and rain, this method is not generally accurate plus, birds can remove stuck flies affecting data.

Monitoring Fly Larvae on Pig Farms

Scrape-and-Count (Common Houseflies)

Pig farmers can monitor fly larvae by simply scraping the top two or three centimetres from the surface of the manure pile. It's essential to test between five and ten sites in that location. Remember that larvae congregate in undisturbed areas and favour especially moist locations. Larval monitoring won't be helpful if there is high footfall or turnover.

As with adult fly monitoring, larval counts should be carried out twice a week between April and October.

Sample-and-Count (Lesser Houseflies)

Lesser houseflies can be sampled from the top of the manure pit using a long-handled tool.

We recommend scraping off around five centimetres from the surface. Put this in a white bowl or tray to make identification easier. It requires skill to separate larvae from pupae! 

Interpreting Fly Monitoring Data 

Data is only helpful if it's correctly interpreted. Identifying different fly species within a trap count and understanding and recording environmental conditions on the survey day are essential to control. These can impact the results.

How Many Flies Are Considered a Problem on a Pig Farm?

There is no official scientific data with concrete numbers; much depends upon stocking density, time of year, location, and fly management programmes. 

However, as a rule of thumb, for resting fly counts, five flies or less is considered normal, but twenty or more highlight a problem. With larval monitoring, more than five larvae indicate that action is needed.

Using the sticky roll test, fly counts of twenty or more of the same species in a week indicate a problem is brewing.

The Clean Neighbourhood and Environment Act 2005 amended the Environmental Protection Act 1990, so insects came under the umbrella of statutory nuisance. The legislation only relates to flies from business premises.

This statute allows local authorities to investigate pig farms if properties in the area make complaints. Complaints can be made about nuisance or fly numbers prejudicial to health.

There is no definition of how many flies constitute a nuisance. Complaint threshold levels will vary from one household to another.

The fact that there's no definitive number of flies to create a nuisance can work in a pig farmer's favour if there are complaints. There's no defined correlation between the number of flies at the source and the risk of nuisance in properties nearby.

Defra offers guidance of a suggested figure of 25 houseflies caught indoors in a domestic building within a 48-hour window, indicating a property with a significant problem.

For the farmer, an essential part of rebuffing local complaints is demonstrating a robust fly management control programme in which regularly monitoring adult flies is an integral element.

It's helpful if data from fly monitoring sometimes accord with complaints from neighbours. This establishes an acceptable threshold for properties in the local area, alerting the farmer when preventative action is required.

Adjusting Your Fly Management Strategy

Fly management strategies should always be under review, and there are many reasons why a fly management strategy might need adjustment. 

Populations spikes arise because of resistance to insecticides, a change in stocking density, particular weather conditions for outdoor units, or a failure to adequately manage the fly population year-round, meaning numbers are out of control.

Regular adult fly monitoring helps identify the cause of a population increase, which makes it easier to implement appropriate adjustments.

Final Thoughts

Flies are undoubtedly a nuisance but don't underestimate their effect on herd health, with reduced feed intake impacting yields and productivity. They also carry serious diseases like Salmonella that threaten animals and humans.

Successful fly control programmes involve various measures designed to minimise numbers and should include the ability to monitor adult fly numbers and record accurate data.

For proven and effective fly control products for all pig farms, shop Dalton Engineering.