A home-made catch-and-release mouse trap with no moving parts

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Fig 1. A mouse in the passive mouse trap. It is unable to find its way back out after entering through the descending tube on the left which ends about 2.5cm above the floor. It can be released unharmed by removing the lid. The wire mesh lining prevents mice from gnawing the corners of the wood and causing damage like that visible on the right. This mouse trap shows evidence of having been used and repaired over a long period.
Fig 2. A catch-and-release mouse trap, consisting of a box and its lid. Visible here on the inside of the lid are the horizontal tunnel and the descending tube, both made of perforated metal. Visible to the right of the photograph is an entrance hole through the wall of the box. This hole aligns with the tunnel on the lid.

This article describes a working, home-made mouse trap with no moving parts. This trap was first shown to me in England around 2019 and I used it successfully 10 - 20 times. At least once it trapped several mice at a time.

This mouse trap is a wooden box about 14cm x 14cm x 14cm with a removable lid and two sides of wire mesh. Mice are attracted by bait such as seeds left on the bottom of the box. Trapped mice are released unharmed by removing the lid. When the lid is screwed down, the only way in or out for a mouse is the descending perforated metal tube visible in Figure 1. The box and its lid separated are both shown in Figure 2.

It seems from my experience that a mouse cannot get back into the tube once all its feet are on the floor of the box, although the reason for this is unknown to me. Usually if any bait was gone, it was all gone and there was a least one mouse waiting in the box. I wrote “all its feet” because once, for a short period of time until I caught it, I did suspect the presence of a rare, clever mouse. The rare mouse, I suspected, remained partly in the tube while stretching down to eat any bait left within reach on the floor below, and afterwards escaped back up the tube. I don't remember how I came to this idea, but it might have been because bait near the tube had gone and bait further away had not. I would generally bait the trap by dropping seeds down the tube, which left many of them directly under it. The way to prevent such cheating would be to place the bait further away from the open end of the tube.

Some measured dimensions

How the maker of this mouse trap chose its dimensions is unknown to me and I have made the following measurements and observations without speculating about which parts of its geometry are more important.

The descending tube and the horizontal tunnel attached to the lid are made of perforated metal (that looks like galvanised steel). They seem to be made from perforated sheet that has been bent to shape and held with twisted wire. They join at the centre of the lid where there is also a second hole to the outside. The mouse can travel along the tunnel and continue down the tube.

The descending tube tapers slightly on the way down. Its lower open end is slightly oval, measuring about 22mm x 18mm across. As Figure 1 shows, this tube descends at a small angle off vertical and that angle is such that the lower end of the tube is displaced about 2cm horizontally from where it would be if the tube were truly vertical. The corresponding vertical drop measured from the inner surface of the lid to the lower end of the tube is about 9cm. This open end is about 2.5cm above the floor of the box.

The top end of this tube is aligned with a 2.5cm diameter hole through centre of the lid, making one entrance to the trap.

Figure 2 shows the second entrance, which is a 2.5cm hole through the side of the box. This hole aligns with the horizontal tunnel attached to the lid. The tunnel is about 3cm deep.