3D Printing Fly Traps

This is the third in what has turned into a three-part series on organic pest control (it’s just that time of year). The previous two posts were on organic wood lice control and white butterfly decoys.

Like most rural dwellers, we accept flies as part of life. Some years are worse than others but wet summers (like this one so far) seem to be very favourable to fly breeding.

We’ve had a few big fly traps over the years like the plastic lids you put on buckets and fill with bait. They work well, but can be a bit big and smelly to use too close to the house. I wanted to design a trap that was smaller, could be deployed nearer the house in larger numbers, and that used recycled materials if possible. It needed to be 3D printable and fit within the constraints of the build platform – 10x10x10cm.

After some messing about with various ideas, The bean can fly trap was born. In a nutshell, flies smell whatever bait and water you put in the can (a small piece of liver, or any offal works well), go in for a closer look, then find themselves trapped. They drown in the can and they in turn, become bait for more flies. The principle of fly behaviour the traps exploit is their drive to fly upwards to fresh air and light; they’ll just keep bumping up against the lid of the trap until they are exhausted and fall in the water.

The two parts of the trap are the lid that allows the flies to enter but not get out again, and a base that can be attached to the top of a fence post. Both parts friction-fit to the can. Most tin cans like this are the same dimensions the world over so it should work with almost any can.

Here are a few prototype traps in testing on top of one of our big traps. I played with various shapes and sizes of entry tunnels, and different vent slot sizes. Getting the flies into a trap was fairly easy if the bait was smelly enough. The harder part was keeping them in there. While we use wet bait to catch and kill the flies, I’ve heard from another user that they use dry bait to catch live flies to give to their pet frog. Either way, I’m happy with less flies in the world.

The plan now is to deploy these traps on fence posts all around the house to reduce the fly population through the Summer.



  1. Gleapsite Says :
    11 February, 2012 at 4:50 am

    Hey John,
    I would love to make some of these… Would you mind posting your 3d design files?


  2. Jackie Says :
    11 February, 2012 at 6:29 am

    Where do you get the plastic funnel tops for these cans. I love the idea of putting them on the fence posts.

  3. gleapsite Says :
    16 February, 2012 at 2:30 pm

    For those interested, the 3d files were uploaded here: http://www.thingiverse.com/thing:6543

    Thanks John, I’m gonna go make some of these!

  4. Adam Shand Says :
    14 March, 2012 at 3:34 pm

    So how did this work? Did it help with the flys? Which design worked best?

    I may have need of your experience soon. :-)

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