Q: I caught a big rat in my squirrel trap. I don’t want to release it, nor drown it.
Is there a humane way to kill the rat?
A: I am not a veterinarian but I would think that carbon dioxide gas could be used to humanely kill the rat (or any other small animal).
Get some dry ice (solid carbon dioxide) from a grocery store.
Get a sealable container large enough to hold the trap and rat. The container should be clear or translucent. A large clear plastic bag would work if it has no holes. A sealable plastic tub could work if you drill a 1/8 inch hole in the lid to allow oxygen and carbon dioxide gas to escape.
Place a fist-sized piece of dry ice on a trivet or thick cloth in the corner of the container, such that the rat can not touch it.
Seal the container but allow a tiny bit of gas to escape at the top. Carbon dioxide will displace the oxygen in the container.
Observe the rat for fifteen minutes. It should slowly cease all movement and breathing. Leave it in the container for thirty minutes after all movement ceases.
Remove the trap and observe the rat inside it for one hour. If euthanasia is complete, the rat will not revive and can be disposed of.
METHODS I DO NOT RECOMMEND:
Exhaust from a car tailpipe: heat and contaminants are not humane to the rat
Ether from diesel starting fluid: ether irritates lungs and causes rat distress before death.
Drowning: death is not instant or painless
Sizing the container.
If the trap or animal is large, a larger amount of dry ice must be used.
2.2 lbs of dry ice yields appx. 125 gallons of carbon dioxide gas. Place enough dry ice in the container to fill its volume four times with gas.