Tuesday, February 10, 2015

Kitten-Proof Mousetrap Mk.II

When I put up my first kitten-proof mousetraps, I quickly found that I had made a mistake. Mousetraps are only effective if approached from the right end, otherwise the mouse can at best escape unscathed and at worst be heavily injured and suffer. Neither would be very desirable, so I modified my design to include a closed end. Here's how to modify a Mk. I to include the closed end. I'm adding the updated size formulas for cutting the cardboard at the end. If you are building from scratch, these instructions go between the folding and the installation of the trap.


1. Mark where your tube should end.
With the tube open, mark that place with a pen. If you cut the long side across the corrugation, it will now make a nice ruler for you.
I left some excess because I had a velcro spot stapled in place that I wanted to preserve. Ideally you can let it end at the end of the trap itself. As always, best leave a little margin.


2. From that point, measure outward a little less than the side's width for the first two sides, that's the inner closing side and the base.

3. Measure out a little more than the sides' width for the remaining three sides.


4. Cut off the excess as shown in the picture. You should get a little step at the second fold:

5. Cut inward as far as your tube end mark from the first step along all four folds. Cut away the part of the outer closing side (that's the fifth side as we're counting here) along the tube end mark.

6. (no picture) Fold in the first two flaps you made along the tube end mark, or whatever corrugation is closest, it's easier that way.

7. Fold in the remaining two flaps one corrugation out from the tube end mark.


8. Glue or staple the lower two flaps together so the inner closing side and the bottom are locked into a right angle.

9. Do the same with the remaining two folds so the back side and the top are also locked into a right angle.

You should now have a construction as shown in the picture, with two right angle half-boxes and a free closing flap. If you did it right, the two closing ends should slide into place nicely without touching.

Congratulations, you now have a cat-safe, mouse-friendly (so to speak) mouse trap.

Last but not least, as promised, the updated size formulas:

Width: unchanged.

Lenght: (L(paws) +L(trap)+Width*1.1) *1.1.

Be sure to include the extra margin as you'll cut some of it back off!

Kitten-proofing mousetraps

Update: This is the Mk.1, which has some flaws which I since identified. Be sure to check out my post on the Mk.II, it will save you some time and effort.

Mousetraps and kittens don't mix. Kittens - or cats for that matter - are curiosity incarnate, and many of the baits we regularly use in mousetraps smell delicious to cats. If your cat gets into your mousetrap, the best case is a broken paw, the worst case is a smashed skull - with all the unpleasant things in between. Now, we have had1 a kitten, and we had a mouse in the larder.

Do not despair, cat lovers, I didn't put my sweet purr machines in danger - and I'd like to share my briliant concept with you, so your cats can purr in safety too. Behold - the kitten-proof mousetrap!




Yeees, the mouse trap is in the tube, got it in one. Here's how to build your own.

1. Measure your cat's arm.

Yes, I'm dead serious. Holes and tubes are even more interesting to cats than anything else, especially if they smell like delicious bacon might be in there, so it has to be long enough and then some, because cats have a strong urge to probe such tubes with their paws. Yes, that could defeat the purpose of the whole project if the tube is too short! 

NOTE: Do I need to mention that if you have more than one cat, you have to measure all of them and use the greatest arm length? Don't guess, cats vary a lot in stance and build. You'd be amazed to find that a 5 lb kitty can actually have a longer arm than a 14 lb tom.

Here's how to measure correctly:

Your cat's arm is built exactly like yours, it has an elbow, a wrist and fingers. Because cats walk on their fingertips basicly the wrist is somewhere in the lower third of the long part of the paw. The wrist is the thing cats sometimes fold under their body when sitting. (See monorail cat pictures for details). Above that comes the elbow. Above that the shoulder.

The best way to get your cat's arm length is to stretch the ellbow with two fingers and your thumb  (don't use excessive force!) and quickly measure from the shoulder to the tips of the (by now probably extended) claws. Make sure your cat is in a good mood, be quick about it and have some bactine or iodine ready just in case. Cats move their arms into this pose when they stretch, so they are not too averse to letting you do it, provided you are polite, quick about it and there's the prospect of some treats.

You will probably have some error in your measurements - try to err on the generous side.


2. Measure your mouse trap.

Mouse traps vary widely in shape and size, so get the measurements of yours lest you complete the project to find out your trap won't work in the tube. The measurements you want are:

  • Width of the trap
  • Total length of the trap
  • greatest height of the trap during the action. Hold the kill bar in place straight up, place the trigger wire across where it would be, measure from the ground. Don't forget the thickness of the base board!

3. Cut some cardboard.




The right material is 3-5 mm corrugated cardboard. It should be strong enough to stand up to some cat attention and mouse teeth, but not so strong you can't get the folds in properly. If possible, cut so the corrugation is parallel to the short side for added stability.

Here's the formulas for the measurements:

Lenghth: (2 * L(paws) + L(mousetrap))*1.1

Note here that I added 10% extra safety margin, because it's amazing how long cats can make themselves if they want something just - out - of - their - reach - almost - got - it...

Width:  5 * (n* 1.1) ,where n is the greater of the width of your mousetrap and the maximum height during action.
Again I added 10% margin, because the folds take up some room and the whole construction gets too tight otherwise.

4. Fold the cardboard.

Corrugated cardboard isn't easy to fold. If you aren't among the few luckies who have a metal folding machine, try the following technique:
 first mark the folds

 then carve in the folds. Use the edge of a two-by-four to hammer in the folds with a rubber hammer (or any other if you're not concerned about the wood)

last, bend the folds carefully. Make sure the bend really follows the pre-cut folds.

repeat for all the other folds. Bend them well to make sure it assembles into a tube flawlessly later. Pro tip: break the folds backward to increase the flexibility.

5. Place the mousetrap


Measure for the middle of the tube you assembled and place the mouse trap there. I like to attach it with velcro spots for easier cleaning/loading etc.

6. Place some velcro spots or strips to hold the tube closed. 



Don't be too sparing with those, that cardboard retains an amazing amount of spring tension and an opened tube defeats its purpose.

Now load the trap and carefully close the tube. There - you're set!


Update: When I designed this, I forgot that mouse traps are kinda directional weapons. Stuff some kitchen tissue paper into the end of the tube that  faces the back side of the mouse trap, or else modify it into a Mk.II which corrects that problem.

1(different story there, not a nice one, gonna spare you)