Following the implementation of a new waste management regime at a large intensive egg production unit, the local environmental health department received a series of complaints from households in the vicinity. Peter Smithers and Nigel Ramsey report on the ensuing investigation.

Over the summers of 1994, 1995 and 1996 residents of properties living near an egg production unit complained of nuisance from flies, which they believed to be breeding in the manure beneath poultry houses. Other complaints alleging nuisance from dust, feathers, odour and noise were also received, as were complaints about the activities of other farmers who removed manure from the poultry houses for use as a soil conditioner on their own land.

Local residents were convinced that the large numbers of flies in their dwellings were originating from manure situated beneath the poultry units. Interestingly, the prevailing wind places the complaining dwellings upwind of the poultry farm most of the time. The only nearby dwelling which is downwind of the farm has reported a fly problem on only one occasion since 1991.

The farm had been granted planning permission in 1991 to construct four additional poultry houses. There had been considerable opposition to the proposals by local residents. Prior to 1991, there had been only one complaint of flies alleged to have originated in the poultry houses and the grant of planning permission was very likely the trigger for the subsequent complaints.

The poultry are intensively reared in houses that are kept at a constant 20oC and with 12 hours of artificial daylight. A stacked cage system is used, where tiers of individual cages are arranged in rows over a mesh floor, which allows faecal material to fall into a pit below the house where it accumulates prior to periodic removal.

This accumulation of manure provides a rich source of nutrients for a number of invertebrates, including several species of fly. These can become a nuisance in nearby dwellings and are well known as potential vectors of bacterial pathogens. The economically important species are the house fly Musca domestica and its relatives. These are found in a wide range of decaying organic accumulations, including manure, but require a moisture content of around 70 per cent to breed successfully. The pits are managed to maintain the manure in as dry a state as possible in order to limit the population of breeding flies. Drier conditions also encourage the incidence of two species of predatory beetles, which prey on the larvae of these flies.

In 1995, a new house was constructed with a new design of manure pit, in that it was open to the elements and had only a one metre high retaining wall to keep the manure from spilling out from under the house. The rationale behind this was that increased air movements in the pit would quickly dry the manure and reduce the fly population.

Unfortunately, east Cornwall has a wet and windy climate which resulted in rain being blown into the pits on a regular basis. This triggered a massive population explosion of houseflies, which in turn generated many complaints from local residents. Environmental health officers visiting the site found large numbers of flies resting on the walls of buildings throughout the site. A statutory notice under section 79 (1) (a, e and f) of the Environmental Protection Act 1990 was served on the company in June of that year and a further notice was served in August.

Following this, complaints were still received from residents in the vicinity of the poultry farm and samples of flies collected from these properties were identified as the housefly. Large numbers of houseflies were also present on the site of the poultry farm.

A summons was issued in the spring of 1996, alleging failure to comply with the notice. This was successfully prosecuted and the company was fined £2,000 plus £9,000 costs. The pits below the poultry houses were bricked up and a ventilation system installed. Environmental health officers subsequently visiting the poultry farm found very low numbers of flies on the site. Despite this, residents continued to complain about flies in their homes to the environmental health department.

During the summer of 1997, complaints were still being received and samples of flies were initially examined by Nigel Ramsey. The fly samples were then taken to Peter Smithers at Plymouth University for more expert identification. The samples typically contained a range of species, many of which would not be found breeding in poultry dung. One sample contained 15 different species, only three of which would be capable of breeding in poultry manure. A wide variety of flies were identified from the samples collected, including hoverflies, cluster flies, yellow dung flies, stable flies, bees and flying ants, none of which had any association with poultry manure.

Despite assurances from environmental health officers the local residents continued to complain about the nuisance flies, which they were convinced originated from the poultry farm. At this time the authors developed the idea of carrying out a survey to identify flies by species and likely larval feeding site. At the end of 1997, the university was asked to conduct an investigation into the flies occurring in the poultry farm and the adjacent houses. This investigation was carried out through the spring, summer and autumn of 1998. A quick and easy sampling technique was required to collect flies from both domestic houses and poultry units. The authors decided upon yellow water traps as these had proved successful in the past, collecting large numbers of flies from rural situations and are simple to install and empty. These consisted of yellow bowls (six inches in diameter and two inches deep) half full of water with a drop of detergent added. Flies are attracted to the colour and attempt to land on the surface of the water where they drown. The catch can then be collected with a tea strainer and preserved in alcohol.

Five site categories were decided upon, six poultry houses, five residents houses, the local water treatment works, the local sewage works, a working dairy farm and two domestic houses many miles from the poultry farm which would be the experimental controls. The traps were placed at the sampling sites for one week in each month between May and October 1998. The insects collected were identified to the lowest taxonomic grouping that enabled the authors to determine the food required by its larvae. Individuals that were suspected of feeding on dung of any kind were taken down to species. A total of 3,445 insects from 86 different taxonomic groups were identified during the survey.

In order to determine the possible source of the flies they were divided into groups based on the food consumed by the larvae (maggots). Two groups were isolated as possible members of the poultry house fauna, those that feed on decaying organic matter and those that feed on dung (other than cow).

A comparison was then made between these flies collected from the poultry houses and those from other sites (see figure 1). This expresses the number of flies from each site as the percentage of flies caught over the year that are able to breed in poultry dung. It is clear that the poultry houses contain a large percentage of insects that breed in poultry dung, but that few other sites have a significant percentage of insects from this group.

The exception is resident three, of which 80 per cent of the insects collected at this site were able to breed in poultry manure. This property was extremely close to the unit being approximately 20m from the nearest poultry house. It also transpired that this household also kept its own chickens and while a small number of domestic fowl are unlikely to cause a fly problem, as this did not come to light until the investigation was concluded it can not be ruled out as a contributory factor.

The only other site to have a significant percentage of insects that could breed in poultry manure was a dairy farm. Samples from this site contained a high number of houseflies which indicate another possible source of nuisance flies in rural areas.

It was clear that most of the households around the poultry unit were complaining about the background incidence of a broad spectrum of fly species that occur naturally in rural environments. These households appear to have been sensitised to the presence of flies by the initial population explosion of flies linked to the new pit management regime and as a result were subsequently annoyed by the smaller numbers of flies normally present in rural developments.

Peter Smithers is an entomologist in the Dept Biological Sciences, University of Plymouth, Drake Circus, Plymouth PL4 8AA. Nigel Ramsey is a corporate member of the CIEH.