Over the thousands of years Humankind has dealt with garbage and other wastes, they have had to deal with the biological duties of Flydom. Though flies are dirty and carriers of disease, the world would be buried in crap and carcasses if it weren't for their intervention. However, they carry disease and are really dirty, so control is an issue.
Some of the earlier controls were to take a certain poisonous mushroom and float it in milk, stinky baits with a similar funnel setup, sticky traps, and the Dog. These forms are not pragmatic for whatever reason, the dog gets full, it takes days to get the stink just right, the stink is stinky, and lack of mushrooms come to mind.
This trap is pleasant enough to keep in the house and works much better, is more efficient, than any of the other methods commonly used.
Step 1: Fly Behavior
The easiest way to do this is to find a big pile of dog crap in the yard and watch it closely. This is a great activity for the family and friends over a few beers during a cookout. We usually cut out little fly wings for the kids and play games like "catch the fly" where one of them takes off making buzzing sounds and have all the other kids chase after them with nets. The dogs join in and it's just fun all around. Anyway, if you watch long enough you will start to see things like me, and realize that when flies get done with whatever they do there, they do two things:
1) They fly straight up.
2) They go towards the light.
See, when flies handle their sacred (Sacred to Flies. What did you think I meant?) functions in the great scheme of life, they seek out stinky dead things all over. If it happens to be in a tight place, they crawl around following the smell until they get to the spot they need to be. Getting back out is a little harder, because in an enclosed space they can't smell anything but stinky, so follow the light. Now you know why they always seem pretty stupid about realizing they can't get out THROUGH the window glass.
The other problem flies have is nobody seems to think of them as pets. Either somebody is trying to eat them, or just plain doesn't like them for some reason. Understandably, they have a real persecution complex, so over the millions of years they've been in existence have developed these paranoid responses which, noting their habits, have worked out pretty good for them.
Beyond the fact that his egress is not likely to be down and under that pile of poop, the most vulnerable time for our leetle friend is when he's taking off. Considering the shortest distance between two points is a straight line, getting airborne is simply a matter of getting there fast. Now catch him.
Step 2: Technique
+ Tin/Steel Cans
+ Screen (Aluminum Wire is my favorite, fiberglass works too.)
+ Glass or Plastic jars
+ Hair Ties
+ Needle and Thread
+ 2 Liter Bottles
+ Reusable/Disposable food containers
+ Spray paint
+ Copper wire (Coat hangers rust unless you paint them.)
My problem originated with attempts on my part to cook a meal out in my yard. As soon as the fire was lit, flies would gather in conspiracy. You could almost see the branches and leaves moving with the masses of them rubbing their little fore feet in anticipation of the hamburger, pickles, and mayonnaise being set out so they could descend in clouds. Then for dessert go across the road to the horse stable.
I could set out the raw hamburger, turn around and lose it in a mass of gray, green, and blue bodies. Needless to say my sex life suffered. I surfed the web for weeks trying to understand my problem, coming across pages of instructions making fools of flies by using 2liter bottles, sticky traps, stinky baits, and learned a new word, "pong!"
Several stinky years of experimentation later, I found a site that gave me a clue as how to design this trap. The model I built, made from 2 liter bottles, caught dozens of flies in the first 15 minutes I set it out. Cheap and easy to build, the open end of the bottle doesn't confuse the flies as much and the light coming from underneath allowed the flies to make up their own minds where to go.
For my second model, I took screen from a cloth screen and stiched it into a funnel with a relatively small hole in the tip of the cone. About 6mm (1/4 Inch), it's big enough to let the fly in and small enough to keep him confused so he can't get out. You will have to decide between longer thinner and short squat funnels, the flies can find themselves out if too short, and can't find their way in if too long.
My last model was to take Aluminum wire screen and fashion the entire cage - funnel assembly out of it. I then placed a riser to hold the assembly off the bottom of a 5 gallon black bucket. My hypothesis being the buzzing sound the flies make as another attractant.
Step 3: Materials and Tools
To disambiguate, I have put together the steps I took in creating the trap in the photograph, which looks pretty good considering the state of my camera. Enjoy!
+ Big Glass Jar
+ Reusable/Disposable food container
+ Elastic Hair Tie
+ Tuna Fish can
+ Plastic Cement
+ Plastic Cement Thinner
+ Sharp Knife (Box Cutter, Exacto Knife)
+ Drawing Compass, or big circle of some kind like an overturned pot.
+ Needle and Thread
Step 4: Cutting and forming the funnel
Roll the screen around to shape the funnel and place it in the jar to see how large you would like it to be. The longer the funnel, the harder it is for the files to get out of, however it will be harder for them to get into as well. In contrast, a shorter funnel will channel the files in more quickly, however the decreased surface of the outside will allow them to more easily find their way back out.
Even the straight edges, trim to an overlay 1 cm (1/2 inch) of the screen, and taking the needle and thread lubricated with beeswax (Beeswax sticks the thread together and stiffens it, making it easier to work with.), stitch a knot at the edge to secure it. Then stitch it closed toward the tip of the funnel. When you get close to the tip of the cone, trim the tip to allow a 6 mm (1/4 inch) hole. Continue the stitching to the end, double the stitch back toward the edge of the cone about 2 cm (1 inch) and knot it there using a double half hitch.
Take the plastic cement and dissolve some with the thinner. It should be very thin, useless for gluing plastic models together. Paint your knots with this, allowing it to soak into the knot and set aside to cure. This will keep the knots from unraveling.
Step 5: The bait chamber
Construction is a no-brainer. Cut hole in lid smaller than the mouth of the jar. Cut slots in the side of the container with sharp knife. Spray paint the outside black and set aside to cure.
Step 6: Assembly
2) Fasten the funnel there by stretching a hair tie over the mouth of jar and funnel.
3) Place bait in used Tuna Fish can.
4) Place Bait Tray in Bait Chamber, attach lid to Bait Chamber.
5) invert Jar-funnel assembly over hole in top of Bait Chamber.
6) Catch Flies.
Step 7: Whuddya do wif em?
Step 8: What should be obvious
1) The bait doesn't have to be stinky. Forget having to find raw hamburger and letting it sit for several days. Leftovers are just fine. Think what flies like, beer, old spaghetti, bread.
2) I like to keep the slots in the bait tray about 1/4 inch. It keeps them from finding their way out of the bait tray back to the environment, and channel them toward the greater light to the cage. More slots allow the smell to circulate, flaps help to keep the light down.
3) The smell is the best attractant. If the smell doesn't get out then the flies won't come to it. While you can construct the trap with solid pieces of plastic cut from say a 2 liter bottle, it's better to just take apart an old screen.
4) You will need to cure the smells from the glue and paint. Flies avoid petroleum because they will get stuck and/or poisoned.
5) Having one big trap will work best in areas where you need to catch a lot of flies, like Cow Barns, Baseball Games, Horse Stables, and Church Socials. Having several small traps set around the yard will catch more flies in the general sense.
6) The longer the traps stay out, the more flies you take out of the local population. That translates into less flies able to breed. I just take the cage and put it in the freezer for an hour or two. The flies grow numb, stop moving, and then freeze to death.
7) If you have Fish, Turtles, or Chickens, you can make food out of them like this. If you want to save your flies, keep them in an airtight jar in the freezer. They get nasty and full of maggots (Yeah Really!) if you keep them next to the fishtank.
8) Save your Tuna Fish cans. Using them as bait holders in the bait chamber saves hours of cleanup time, especially after the flies have started a little family in the bait there. Throw out the old bait, rinse out the can, put in fresh bait! Breeding flies would be self-defeating...
9) Having other foods around like an uncovered trashcan will attract more flies. They will want to hover there rather than the smell of the trap.