Farm-Yard Flies
Household Fly Picture		Household Fly Diagram Details

A Case Study
Over a period of several years, a number of farmyards in an area near Miami, Manitoba, Canada had suffered a serious problem with nuisance flies entering homes in the late summer and early fall. A great deal of money had been spent on pesticides in efforts to control the problem, and on fly-proofing homes in the problem area. While proper management practices around the homes and barnyards were employed in attempts to prevent the problem, the situation did not seem to improve.
 
 
 

In late July 1998, the Deerwood Soil and Water Management Association contracted Prairie Pest Management (PPM) of Carman, Manitoba, Canada to conduct a fly surveillance program at the most seriously affected farmyard. Since the proper identification of the flies is necessary in order to determine a management strategy, fly surveys were conducted to determine the species of flies involved and the relative numbers.

Flies were collected, counted and identified on a more or less weekly basis from early August to late September. Flies were collected from, and/or counted on grain bins, a tool shed, an adjacent slough and on the exterior of the two farm homes in the yard. Of all the sites monitored in the yard, by far the largest number of flies had gathered on the two homes. There was an increase in fly activity in the yard as fields in the area were harvested. 
 

The species causing the fly problem in the yard was Cluster Flies - making up about 95% of the problem. Although other flies were present, such as hover flies, they were not considered a nuisance since they normally do not gather on, or enter homes.

The study also identified a sharp, short-term increase in numbers of cluster flies on the 20th of August, coinciding with liquid pig manure spreading on a field just west of the site the day before. (see graph) It was a hot and windy day, and the odor plume from the manure moved over the yard. Since cluster flies are not known to follow odor plumes, it is possible they may have simply been moving in from surrounding fields, seeking shelter of the trees around the yard, or moving toward ravines in the area for shelter. However, circumstantial evidence points to the connection of the two events.
 
 

	Aug 6	Aug 13	Aug 20	Aug 27	Sept 9	Sep 16
Grain bins	2	7	11	17	37	6
Home #1	11	15	165	8	58	52
Home # 2	n/a	n/a	127	50	45	37
Slough	1	7	1	6	4	1
Tool Shed	n/a	24	14	16	8	19
Total Cluster	0	5	292	54	91	78
Total Other	14	48	26	43	61	37

The study concluded that since the high populations of nuisance flies in the yard were cluster flies, the problem was not the result of poor manure or livestock waste management practices. Cluster flies lay their eggs in the soil, not in manure or garbage. They feed on nectar and sugar from fruits and flowers and on honeydew material deposited by aphids feeding on trees, not on manure, carcasses and the like.