Introduction
For many people, signs of spring are crocus plants peeking out from underneath a thin layer of snow, robins singing in budding trees, or big, bumbling flies buzzing and banging up against windows. At first glance they resemble houseflies; however, they are larger, darker and slower in their movements. These flies are commonly referred to as cluster flies and can be abundant in houses with large lawns or those backing onto open parks. The name "cluster fly" is derived from their habit of entering a house in the fall and gathering in clusters that may emit a sickly, sweetish odour if disturbed.
Cluster flies hibernate in secluded areas of houses, such as in wall voids, attics, closets and empty rooms. They are a particular nuisance as they leave stains on the walls and curtains. If the flies die in the wall voids they may attract larder beetles, which will feed on the dead flies and then migrate to other areas of the house. In the spring, the sluggish cluster flies will migrate from their hibernating areas to living spaces and gather on windows as they are attracted to light.
Description of Cluster Flies
Cluster flies (Pollenia rudis) belong to the same order as fruit
flies, houseflies and mosquitoes (Diptera). Adult cluster flies are
approximately eight to 10 millimetres long. They are dark grey with black and
silver (non-metallic) checkered abdomens, with many golden hairs on their thorax
(these may or may not be present on older flies). Their wings overlap when
they are at rest.
Lifecycle
Cluster flies are parasites on our friendly earthworms. The eggs are deposited
singly into cracks in the soil of lawns or open areas in late summer or early
fall. The eggs hatch in approximately three to seven days and the larvae then
enter the body cavities of earthworms to overwinter until spring when feeding
activity resumes. The larvae feed for up to 19 days; they then moult and begin
the final larval stage. The larvae finish feeding on what is left of the earthworm
hosts and then enter the soil where they pupate for approximately 10 weeks.
In mid-summer, adults emerge from the soil. These adults and the cluster flies
that hibernated in households will mate and lay eggs in late summer or fall,
repeating the cycle. Adult cluster flies can often be seen sunning themselves
on stumps of trees and sides of houses in autumn before they hibernate.
Prevention
Cluster flies can enter the home through the tiniest crevices around door
and window frames. To prevent infestation, ensure that all screens fit properly
and that there are no cracks or holes which would allow them to enter into
the house. Weatherstrip windows and doors, fill any cracks or crevices around
door and window frames with caulking, and screen air vents in soffits.
Physical Control of Cluster Flies
Non-pesticidal means of controlling cluster flies include using a fly swatter (be aware that an unpleasant odour will be released when a fly is killed), releasing flies outdoors or vacuuming them up and then disposing of the bag.
Chemical Control of Cluster Flies
If the infestation is severe enough to warrant the use of pesticides, products containing the following chemicals are registered for controlling cluster flies: piperonyl butoxide, pyrethrin, permethrin, d-trans allethrin, n-octyl bicycloheptene dicarboximide. These products can be purchased in hardware or grocery stores and garden centres. They can be sprayed around the exterior surfaces of window and door frames to prevent entry. There are also products that can be sprayed on interior window and door frames, baseboards, floors, floor coverings, underneath furniture, and in closets and crevices and other places where insects hide or are seen. It is important to read the label carefully and use the product according to label directions.
It is not advisable to control cluster flies by attempting to control the earthworm population because earthworms are the most natural means of producing fertile soil and the cheapest lawn aerators.
|
