How to make the fly traps

Materials

To construct the traps detailed on our flytrap project page you will need:

  1. two same-sized, empty, drinking-water bottles. Those shown are 10 litre capacity, but 5 litres or even 1.5 litre bottles work perfectly well
  2. two black polythene bags (found absolutely everywhere in Kenya & Tanzania)
  3. some sisal string or cloth strips
  4. six large acacia thorns found almost everywhere
  5. a sharp pointy knife or blade

Construction

To make the top section of the trap, slice the bottom off of one of the bottles. If the bottle is ribbed, best to cut at the lower edge of one of the raised ribs, rather than in the grooves. This helps with fixing firmly on the bottom section of the trap later.


Cut the excess neck from the second bottle. The plastic here is quite thick and it takes a fair bit of effort to do this. Heating an old knife in a fire might help, though burning the plastic with a knife that was too hot may cause a burnt plastic chemical smell which might deter flies from passing through.


Place the first cut bottle over the second whole bottle. It should sit very snugly, especially if care was taken over the cutting. Ideally there will be 5-10mm where the plastic sides of the top bottle are flush with the curving top of the bottom bottle and this is where holes will be drilled through the plastic of both bottles to insert the thorns for fixing. If the top bottle was not ribbed, then slits can be cut vertically in the top bottle and this will allow it to push snugly over the bottom bottle.


Lay the two bottles on their sides, and with the tip of a sharp pointy knife "drill" about six very small holes through both walls of the bottles, evenly spaced around the edge. This should be done where the top bottle sits flush and snugly on the bottom bottle. Don't press too hard, and twist the knife rigorously, so it will "drill" a hole rather than cut a slit. Only make very small holes as pushing the acacia thorns through later will enlarge them as necessary to hold tightly.


Using a single large acacia thorn, with a little of the base bark still attached, push through the pre-drilled holes


Cut two or three entry slit "windows" around the base of the bottom bottle. They should be cut about 30 mm up from the bottom with an overhanging "flap". The openings should be about 10-12 mm deep and 50 - 60mm across. They should be cut on three sides, and folded out along the top edge - see detail below. 


Detail of the entry-slit opening. Fold the "flap" out along its top edge. When the flap (but not the hole) is covered by the black polythene bags it deters flies from exiting through the entry slit. It will also prevent rainwater from running into the trap and causing the bait to overflow. 


Cover the bottom section of the trap bottles with double thickness black polythene bags, including the base. In this case the bags fit fairly snugly over the bottom bottle. Fold the bags back on themselves if necessary so that the whole of the bottom bottle is darkened, leaving the top bottle clear and light. They can be tied in place with string or cloth strips if necessary.


Locate the pre-cut entry slits in the bottom bottle and cut away the black polythene bag where it covers the holes. If the bags are loose fitting, you may need to remove a small amount of black polythene to allow clear access room for flies to enter the slit, but don't remove so much polythene that there is not enough to cover the overhanging flap.  This helps keeps the bottom dark and deters flies from leaving through the entry slits.


Not the best pic I'm afraid but it does show the entry slit and the flap still covered by black polythene.


Sisal string (or cloth strips) can be used to hold the polythene bags in place. Again this is a bit messy  and could be neater with a little more time spent on construction.


With the tip of a knife drill a few air ventilation holes in the top bottle. Obviously don't make these large enough so the flies could escape. This prevents condensation in the top bottle (which may prolong the life of the flies if they drink the water), and even cause them to rot rather than simply dehydrate. It also keeps the air in the top bottle relatively "fresh" to ensure flies are not put off from entering by high concentrations of unfavourable gasses or maybe low concentrations of oxygen.


Another length of string can be tied around the neck of the bottle for hanging.  Now carefully pour in milk, meat scraps, food scraps, sugary water (it doesn't matter if some spills or gets spread around the entry slits - just adds to the attractiveness) and VOILA!

Hang somewhere off the ground so it isn't knocked over by children, animals or wind. Empty, clean and check bait after every 3 or 4 days.


Thousands of flies caught in a 10 litre bottle trap after two days in a Maasai boma. Maybe enough chicken food there to convert into 1 egg! Now that's recycling sustainable fly harvesting .... mmm tasty......

Site updated on 15th May 2022

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