A better mousetrap

Many years ago I made a humane mousetrap ago because my family don't like the idea of the spring "snap" trap. I don't really either, partly because when I was a kid my father used one and I saw plenty of mice that had not been killed cleanly . Besides, I just like making things.

This trap is pretty old now and no longer works reliably, but it's given good service and in the 15 years or so it's been used, it's caught probably over a hundred mice. However, the old design was over complex and a bit tricky to set. It had a drop-down door held open by a thin bolt that was withdrawn by the mouse walking over a see-saw. Setting it was always a balancing act between having it trigger by itself or not having it trigger at all. I thought I could do better.

The old trap showing signs of wear, and being eaten

The new design has a pivoted door, is simpler, smaller and seems to work well, so I'm describing here how to make one.

The new one is much smaller!

Here's the schematic:

The trap is a simple box - two sides, base and back - with a hinged door and hinged wire mesh on top. The top could be another piece of ply, but the mesh lets you see into the trap when the door is closed. The top needs to be able to open so the see-saw can be removed for cleaning - it's essential that mouse droppings are removed from under the see-saw or it will not "rock" properly.

The materials were chosen from scraps I had lying around (I hate throwing away offcuts). The carcass of the box is made from 9mm plywood, and the see-saw and door from 5mm ply. Neither of these thickness are critical although the mesh is hinged with small staples in the top of the back, so this cannot be much less than 9mm. If you do change the thickness of any pieces, check that this hasn't changed any of the other dimensions.

The box carcass (sides, back, base) should be simply glued together with wood glue.

Cut the see-saw so that it fits inside the box with about 1mm clearance from the back and sides. Fit the wire door support next. It's a square hoop that the door rests on when open. I made this and all the other wire pieces from some 1.6mm galvanised wire I already had, just pushed into holes drilled with a 1.5mm drill bit. This was a bit lucky - the combination of bit size and wire size meant that the wire is held firmly in the hole without anything else being needed. You may need to search around to find something suitable. Thin coat hanger wire may work.

With the door support in place, find the balance point of the see-saw by placing something suitable under it. Then mark the position for the screws as 2-3mm back from this balance point, so that the see-saw will naturally rest forward but will tip back with the weight of a mouse. Place the see-saw in the box as shown in the diagram, and check it balances easily on the screws and doesn't touch the sides, then press firmly down on it so the screw make indentations in the base. Don't press too hard - you are just trying to make indents so that the see-saw will easily locate itself when you put it back after cleaning.

Drill holes in the sides for the door pivots - make sure that the pivot line is at right angles to the sides or the door will catch against the sides. Hold the door in the right position and then push wire through the holes on each side so that they mark the door where holes should be drilled. The holes in the door should be wider than the wire so the door swings freely. You can see from one of the picture that my door is sloping slightly backwards because it's fractionally longer than the opening. This actually works well - you don't want the door to be able to be completely vertical as it could be pushed open.

Once the door is in place, bend the door support as needed so that the door just rests on the wire when the see-saw is at rest (forward), and closes when the see-saw is tipped. You will need to fiddle around with this to get it just holding the door open so that the slightest movement of the see-saw will release it.

Cut some wire mesh to cover the top and loosely staple to the top of the back so that it can hinge back to give access to the inside. Drill holes in the top of the sides to take wire turn catches to hold the mesh in place.

Finally you should seal the inside with water-based varnish. Mice will make it wet and messy when they're inside.

For bait you don't need anything special - contrary to popular opinion, mice don't have any special preference for cheese. I just use a few crumbs of digestive biscuit.

I release the mice a little way away from the house so I can be sure they don't come back. I've no idea if they are likely to, but I did read a comment left by someone who had bought a humane trap. They were complaining that it was useless because the mouse kept returning. This person didn't seem to consider that they may all have been different! In my experience it's normal that you don't just have one mouse -  "catch one, catch more".

That's it. I hope it's useful.