“I ended up changing out the flimsy plastic to a combination of 1/4 plywood and screen fabric.-4-6-12 GN”
I will always trade one single large effort for several smaller ones, this is the inspiration for most of my projects. I want to create something that will work for years to come with little or no maintenance and comes with only initial cost. It is with these philosophies that I bring to you project fly trap.
First off, this trap will not replace my other efforts at fly control. I am still using fly predators to kill off flies while they are in the pupae stage plus I use some chemical sprayed on a back rubber that the cattle can use at their convenience. I also believe it will take more than one fly trap to really make a difference; anyway I needed project.
Think of this fly trap as a four-sided pyramid that rises to a platform which has a four inch hole in it. On top of the platform is an upside-down funnel that leads into a canning jar which is also upside down and mounted to the platform using the canning jar lid. The premise of this trap is that flies will always fly to the light and upwards, they also can find a small opening if it is at the end of an angled wall but cannot find that same opening when it sits in the middle of an open space.
I began the trap with four uprights made from treated 2×2 wood cut to 84 inches long with one 45 degree end. These four uprights are mounted with metal brackets to a nine inch square plywood platform. I brace the uprights with 2×2 wood cut to 57 inches with a 45 degree cut at each end. These horizontal braces should actually have a compound cut to fit perfectly on the uprights but one cut makes the fit pretty close and metal brackets will hold it firmly. The plywood platform will need a hole cut to match whatever canning lid and jar you decided to use. You will also have to make a compromise between the size of the lid and the size of the funnel which will sit upside-down on top of the canning lid and inside the jar. I found that the Rubbermaid square container and a small yellow funnel worked together perfectly, although I had to carefully cut a hole in the lid of container lid to match the funnel opening.
Frame complete, you will need to cover the frame from the braces (about 24 inches from the ground) all the way up to the plywood platform. The bottom 18 inches must be dark and the rest of the covering must be see-though or screen. Now here’s the secret of this project, a big black ball. You must hang a large , black ball in the middle of pyramid to attract flies and it must hang so about half of it hangs below the bottom of the dark fabric covering the bottom of the pyramid. I couldn’t find a black ball so I painted two milk jugs black and used them instead.
The is how the trap works. Flies believe the black ball is the belly of an animal, find it does not have any blood to harvest and then fly off with in the pyramid. They will always fly upward past the black fabric of the pyramid towards the clear plastic or screen place at a higher level on the pyramid. When they find they are still trapped they will crawl upwards through the hole in the plywood platform then continue upwards through the container lid/canning jar lid and follow the upside-down funnel through it’s small opening and into the light of a clear plastic container or canning jar. They will then be unable to find that opening to leave the jar and eventually perish.
I’m not sure the size of the trap is that important as I have seen commercial models ($300) much smaller than the one I made. Start with the dimension and instructions in my column but use your common sense and remember the basic premise of the trap as you design your own model. You can also search several agricultural extension websites for more information using the search term, “Manitoba fly trap.” I made my trap for about $40 but if your heads swims at the idea you can always purchase a commercial model. I always feel home made is best, however I’m sure the flies really don’t care.