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Insect Control at Redwood Hill Farm

Includes Mother Nature's Fly Trap

Scott Bice & Steve Considine

The fly trap used by Redwood farm.
The fly trap used by Redwood farm.

We are totally committed to protecting our environment and the health/safety of our employees and goats. Therefore, we have a policy of zero tolerance for synthetic chemical pesticides. Cleanliness and sanitation are the first line of defense against such pests as common flies. Their larvae need a moist, nitrogen rich area in which to incubate and hatch. In so far as possible, such habitats are minimized in our management.

However, certain areas are always problematic on a working farm, such as around and underneath platforms supporting water tanks. Insect predators are routinely distributed to such areas to feed on the fly larvae. We allow swallows to nest under the eaves in the outside peaks of our barns. Seasonally these swallows are constantly busy swooping through the air to catch flying insects to transport back to their mud dabbed nests to fill the ever-hungry mouths of each fledgling hatch. Literally thousands of insects are needed each day to feed these babies. This is a self-perpetuating cycle, as these young birds will return to these same nests each year after their southern migration for the winter. One can almost time their return towards the end of April, and a flurry of activity will again occur under the eaves as nests are repaired, prior to the laying of eggs in preparation for the newest hatch. Inside the barns and milking area, large reels of sticky tape with a naturally occurring fly attractant, but no pesticide, are strung at the ceiling. Flies land and cannot take off. Each day these reels are wound so that the fly covered tape is replaced by new tape. This patented product is available from agricultural supply companies.

Still, the battle against flies demands other more drastic measures. About 25 years ago, we had a very inventive employee who garnered the nickname of Mother Nature. She was constantly trying to improve on various products available commercially. Her creativity was boundless, as was her enthusiasm. She set out to improve on the original “Big Stinky.” As a cottage business, she began designing and assembling large flytraps to sell to the farm. As she refined her design, such traps became more and more effective. She no longer works for the farm, but her legacy endures in Mother Nature’s Fly Trap. The original traps are slowly disintegrating and often need to have extensive repairs and/or rebuilding. This is now an annual spring maintenance project. Currently, there are about 20 of these large fly traps in use at Redwood Hill Farm. Visitors often ask about how these traps work and instructions to assemble and maintain them.

First of all, a bit about fly dining habits. There is a bait tray at the bottom of each trap with a fermented mixture of two food grade ingredients in water. As it ages, it smells like something dead and flies will enter the bottom of the trap to get at such a delicacy. The interior of the trap immediately above the bait tray is an inverted mesh screen cone which narrows to about three inches at the top. Once a fly has eaten its fill, it usually likes to fly straight upward towards light, which in this case is at the top of the cone. For whatever reason, no fly has yet mutated to the extent that it can figure out how to escape by going back down that same cone. The more flies that are angrily buzzing around in the top of the trap, the more flies will enter the base of the trap to participate in the feeding frenzy. The captured flies eventually dehydrate and drop dead. As these accumulate and build up around the cone in the trap interior, less and less light will be visible at the top of the cone to lure flies to their fate. Routine cleaning to remove dead flies is necessary; chickens regard desiccated fly as a special delicacy! During the cleaning, the screen mesh should be carefully sprayed with water to remove accumulated dust and cobwebs. Flies prefer a clean, well-lit trap. An extra bonus during yellow jacket season is that they will enter the traps not for the bait, but rather to feast on still living flies. They appear to be no smarter than their prey, cannot figure out to go back down the cone, and dehydrate and die as well.

The bait recipe

In a small pail containing 1/2-gallon of warm (not hot) water, use an egg whisk to blend in 1 1/4 cups active dry baking yeast, and then 1 heaping tablespoon of ammonium carbonate (a powdered leavening agent used in certain types of baking; available on line at spectrum.com) Pour into a one gallon plastic bottle. Plug the top with a vapor lock such as is used in home brewing; this simple device allows gases to escape during the fermentation process. Place in a warm place out of the sun and let it age for at least two days prior to use. Place a 9″ disposable foil circular cake pan at the bottom of the trap, fill half way up with bait, carefully position in the center under the cone. As the bait dries out, refresh with additional bait. Eventually this foil container will be full of dried bait. Discard in a sealed garbage bag (otherwise the flies will attack your garbage containers!). Fill and insert a fresh bait tray. Because of the smell when handling, the use of disposable plastic gloves is recommended.

How to assemble a trap

You will need a piece of galvanized 2″ x 1″ welded wire, 24″ wide and 36″ long, with no points protruding on any side. Form this into a cylinder with the 24” sides meeting and attach together with cage clips, available at most hardware stores. On one end which will be the top do not clip the last two inches together. At the other end which will be the base and opposite to the junction, use diagonal pliers to cut off 2″ x 10″ of the wire (this will be where the bait tray can be inserted). Set aside. Now the hardest part! Use a concrete forming tube about 11 1/2″ in diameter. Mark around the tube at 22″ from one end. Cut a piece of aluminum mesh window screen 30″ in width and 42″ in length. Roll the screen around the tube at the line, with 10″ of screen extending beyond the end of the tube. A set of helping hands would be very useful at this point. Temporarily remove the screen from the tube, marking where that 10″ line is. Flatten the screen and mark at 9″, 18″, and 27″. Use a straight edge to fold over and crease at the 10″ mark again. Flatten. Firmly crease triangular sections of the screen folding upwards from the bottom at the midpoint of the three marks towards each mark. These folded over triangular sections will form the top of the cone. Then flatten again and reposition on the tube, with the 10″ protruding with the creased sections. Hold the 3″ overlap of the screen from each side firmly together and fold around a yard stick at least twice, tightly creasing each fold. Using a large common paper stapler, staple the folded screen together as your helper slowly pulls out the yard stick towards the 10″ end. Do not yet staple the 10″ which will form the cone. Gently invert those 10″ into the tube and slip the mesh off the tube. Reach inside to overlap the triangular sections one at a time and staple together; overlap the unstapled end section and staple firmly. The hardest part is now done.

The tedious part begins

Carefully insert the screen into the wire cylinder with the cone at the same end as the opening made for the bait tray. There should be 2″ of welded wire below the bottom of the mesh cone. At the top of the welded wire cylinder and beginning where the two ends are clipped, carefully align the stapled seam of the mesh screen. Use very fine gauge vinyl coated electrical wire and weave through the mesh at every 1″ spacing from inside out and then over and repeat 36 times. (Do not weave through the stapled seam to allow flexibility.) Weave snugly but very delicately so as not to distort the mesh. Wrap the ends around the welded wire on either side of where it is clipped together to allow for some adjustment when fitting the lid. Using cable staples carefully tack the base of the trap in three of four places to a pre-painted 12″ square of 3/8″ to 5/8″ exterior plywood. Use a standard five gallon white bucket lid (preferably white) to make the top. Drill a 2″ circular hole in the center. Cut a 3″ square of acrylic plastic, position over the hole in the lid and attach at two opposite corners with 3/4″ No. 8 self-tapping hex head screws. Very carefully push this top onto the trap, being sure not to crunch the mesh downward. The groove intended for the bucket should snugly hold the upper part of the trap. Some flexibility is possible because the top of the cylinder was not clipped together. To form a handle, either use a heavy gauge insulated electrical wire or heavy gauge wire with a piece of flexible drip irrigation tubing slipped over it. This should be about 30″ in length and attached by twisting to itself on opposing sides of the trap to the welded wire about 4″ from the top and well away from the join in the welded wire.

Mother Nature’s Fly Trap works best when clean, freshly baited and placed in the full sun. If a trap fails to attract flies, it may be that spiders have spun a web in the cone. Carefully remove the acrylic square in the lid and use a long stick to carefully swish around the interior of the cone to remove cobwebs. Keep the acrylic clean. Always refresh the bait after rains.


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