A viewer on my HGTV program asked: "Does the type of siding make a difference in attracting Cluster flies?"
I always wanted to learn more about those flies that cluster on the side of houses (usually in the country) and mass in the windows in the early spring and late summer. They are larger and slower than house flies, and smell a bit bad when you swat them. So this question let me put the staff into research mode. Here is what we found.
Where do they come from?
These flies are called "cluster flies", and their life cycle is quite interesting, because it explains why we find them where and when we find them. They start out as parasites on grass that move into earth worms. They spend the first winter inside the earthworm. In the spring they kill the earth worm host but this start of their life explains why we usually find them in houses that have large well fertilized, well drained grass areas adjoining the house, as is typical in the country. This grass has lots of worms. At the end of the summer they mate with last year's gang and lay more eggs. They often sun on house siding in the early fall before moving into the house attic and walls where it is warm enough to allow them to hibernate for the winter. In the spring, while the next generation is hatching, this generation wake up and try to get outdoors in order to feed on pollen -- clustering on the inside of your windows -- thousands of them.
So the answer to your question is "no". The type of siding doesn't really make much of a difference -- it is the quality of the well drained grassy area that causes the presence of the flies, or more precisely the population of earthworms that causes the presence of the flies.
It is possible to get insect repellant paint additive to add to any paint, or special and very effective insect repellent paint-like transparent coatings to apply around any entrance paths. If you spray these around all openings to the house, you can reduce the number of cluster flies that enter your house -- they are not born inside, they migrate there. One of the transparent coatings is "Insecta" water based latex pest control coating, usually sold for roach control. If you have aluminum, vinyl, or wood siding, it is probably not worth trying this cure, because there are just too many holes for them to enter -- unless you want to paint the whole house. With brick or stucco siding you can concentrate on the cracks and holes. You will have to repeat the process every two years; that's why adding it to house paint is not such a good option.
Eco Frendly Traps
To get rid of existing cluster flies, many people simply vacuum them up and empty the vacuum outdoors. There is a newly patented Canadian invention (new meaning 2001) called the Cluster Buster, that has the remarkable ability to attract and immobilize up to 1000 Cluster Flies when placed on the inside of a window pane. The very finely ground eggshell power inside the trap acts like "quicksand", preventing the flies from escaping, and once the traps are full of flies, they can be disposed of in the normal household garbage.
The Cluster Buster traps will work for other insects as well, particularly ones that gather on the windows trying to get outside. They have specific traps for Ladybugs and for Boxelder Beetles with additives that attract those insects.
You can get the Cluster Buster at Co-op outlets in Ontario, some Home Hardware stores and some garden centres. I found Powder Trap Quyicksand for Bugs on the web as well which uses the Cluster Buster trade mark and sells all three types of traps.