Make Your Own Fly Trap

What looks good to horse flies? Horses. And for some reason, so does this trap. It may not look attractive to you at first glance, but when you see the results you will love it. Also, it is environmentally-friendly (except to biting insects!), no chemicals are needed, and easy to sew and construct yourself.

The trap is about the size of a horse. Here is one made by Marjorie Smith of "Barefoot for Soundness," www.barefoothorse.com. She says the fabrics cost about $25; everything else was scrounged; and it took most of a day to make. Given that it stays out in the weather all summer, it will last one or two years.

The Nzi Trap

Through extensive research, it has been found that this unique trap, known as the Nzi (EN-zee) trap (‘nzi' is the Swahili word for ‘fly'), effectively catches biting flies. Originally designed to trap the dreaded tsetse fly in Africa, it is now being used worldwide, thanks to the generous sharing of information on the internet - at http://informatics.icipe.org/nzi/index.htm, hosted by the International Centre of Insect Physiology and Ecology - where you can find lots of interesting details about this trap and its variations, and flies.

It works via the attraction of flies to large blue and black objects. Once they get inside this clever configuration of cloth and netting, which they readily do, they can't find their way back out and they die in the collector.

The trap is made from simple shapes for economy, and for ease of assembly. The layout is triangular with all pieces cut to the width of the material (e.g. one meter, one yard). Compare the photographs to the diagrams to understand the layout and the geometry of the components (external poles are shown in the photos; internal poles in the schematic).

The trap walls are formed by a square piece of netting at the back and by two black cloth rectangles at the sides. The body is closed at the top front by a vertical blue shelf. Two blue rectangular "wings" extend out at an angle from the front. A trapezoidal piece of netting extends horizontally half-way into the body from the bottom of the blue shelf. The top is closed by a 3-sided "cone", made by cutting a wedge out of a square piece of netting and sewing up the sides.

Materials

  • Fabric (see specifics below)
  • 3 metal posts
  • 3 dowels or similar reasonably rigid poles
  • 1 flexible rod (fishing pole or old longe whip)
  • 1-liter clear plastic soda bottle (cut neck off at widest part - use neck as funnel, bottle body as collector)
  • wire
  • string
  • duct tape

About the Fabric

Flies are attracted more to heavy-weight, opaque, rough-textured/ twill weave, non-shiny fabrics, and in 100% cotton - although polyester-cotton blends will work.

Flies go under, around the baffle, up, through the funnel, into the collector bottle, and into the collector bag, never to escape.

Please note that the choice of the right kind of blue fabric is critical due to the color's peak wavelengths. [Although exact reflectance profiles and peak wavelengths vary, most blue fabrics used for tsetse have Commision Internationale de L'Eclairage (CIE) dominant wavelengths of 478 nm (including the polyester/ cotton blends). Phthalogen Blue Cotton Drill is the most effective colored fabric used in Africa, however Sunbrella (Pacific Blue, # 4601) seems to work effectively in North America.]

For more info on fabric choices, see http://informatics.icipe.org/nzi/Nzi_trap/Fabrics/Fabrics.htm

Measurements (you can substitute yards for meters if cloth comes in that width):

  • 2.5 meters of 1-meter-wide white non-shiny netting
  • 1 meter black cloth
  • 1.5 meters blue cloth

Construction in Ten "Easy" Steps

1. Cut out two rectangular pieces of blue (100 x 55 cm or 1 yd. x 20 inches) for the front wings. The extra 5 cm is for a sleeve to hold thin bamboo poles. These supports give the trap shape and distribute tension evenly across the fabric. Fold back 2.5 cm from the edge, and sew down to make a sleeve.

2. Cut out two black rectangular pieces (100 x 50 cm or 1 yd. x 18 inches) for the side walls. Attach each blue wing to each black side on the long edge, keeping the sleeve of the blue wing to the outside.

3. Cut out one blue rectangular piece (100 x 50 cm or 1 yd. x 18 inches) for the top front shelf. Fold back each blue-black piece at the seam; lay out with the blue facing up and the sleeves to the outside. Sew the short side of the blue shelf to the upper, inner half of one blue wing. Attach the other end to the other blue wing in the same fashion.

4. Cut out a rectangular piece of netting for the inner shelf (100 x 50 cm or 1 yd. x 18 inches). To make a trapezoid, mark 25 cm/ 9 inches in from one corner on a long side. Draw a line to the adjacent corner and trim the triangular piece off. Repeat for the other corner. You now have a trapezoid with one long side (100 cm or 1 yd.) and one short side (50 cm or half a yard) that is 50 cm/ half-yd. wide.

Within minutes after assembly, there are already three flies and dozens of gnats in the trap. Mosquitoes get trapped too.

5. Lay out the blue-black assembly flat on the table with the black-blue vertical pieces together back-to-back. Keep the black side towards you. Sew the long side of the trapezoidal piece of netting to the bottom of the blue shelf.

6. With a white marker (e.g., chalk or a thin wedge of soap), draw a line across the middle of the black sides. Match up with the sides of the trapezoidal netting and sew the netting to the black. The assembly is bulky at this point, so be careful not to inadvertently sew into multiple layers of cloth. At the junction of the blue, black and netting, sew into previous seams to close up any gaps.

7. Cut out a 105 x 100 cm (38 inch x 36 inch) piece of netting to form the back of the trap. Fold the netting in half along the slightly longer side, and sew a line 2.5 cm (1 inch) in from the middle. This will form a sleeve at the back corner of the trap.

8. Attach the netting to the back of the black sides to close the body. You should now have a symmetrical triangular body that will be slightly less than 1m x 1m x 1m (1 yd. x 1 yd. x 1 yd.), depending on your seam allowances. Confirm the dimensions so that you can adjust the size of the netting cone, if necessary.

Construction and design

9. Cut out a square 100 x 100 cm (1 yd. x 1 yd.) piece of netting to form the cone. Mark the exact center at the intersection of diagonal lines drawn between opposite corners. Cut out a triangular wedge from one side. Match the 1-m sides of the cone to the 1-m tops of the body and sew the cone to the body. The triangular wedge removed from the cone is about the right size for use as a netting sleeve/collector bag with a bottle-type trap collector. Cut wedge in half and sew the two triangles together to form a 50 x 50 cm (half a yd. x half a yd.) square. Fold this in half to make a 25 x 50 cm (9 inch x 18 inch) rectangle. Trim the width to fit the bottle circumference. Sew down the top and the open side and you will have a practical sleeve/collector bag.

10. The Completed Trap - To finish, match the opposite sides of the netting where the wedge was cut out, and close up the cone. Leave a small opening at the top for insertion of funnel/neck of bottle. Check all corners for any inadvertent gaps at the seams. Stretch the trap out between three poles to check on symmetry. Sew a tuck into the horizontal shelf if it sags in the middle. Cut a small hole in body of bottle exactly the size of the top of the bottle. Insert the top of the bottle up through the opening in the netting and screw it into the hole in the side of the bottle. Use wire and string to reinforce this connection. With wire loops, string, and the flexible rod, the bottle and netting are suspended. (See photos.) Duct tape can be used to hold netting collector bag onto bottle body so that it doesn't pull apart on windy days; the bag can be removed to be emptied when it becomes full.

Fabric pieces

Attractants have been tried, however the number of flies trapped with attractant was not much more than without attractant. The trap works amazingly well by itself.

Place in an area near but protected from horses, and out in the open where it is visible from all sides. It works best in North America when facing west or southwest.

For more information:

http://informatics.icipe.org/nzi/index.htm

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