Step 6: Wild Animals - Lethal - Poison
A method my uncle used for mice is uncooked instant mashed potatoes. The mice eat the instant potatoes which expand in their stomach which crushes their organs. I imagine this might work for other small rodents.
This next method is not recommended but for the sake of completeness I'll mention it. A different uncle killed of a family of groundhogs using chlorine gas. He blocked off all the entrances to the burrow except one. He then poured ammonia and bleach down the hole which generated chlorine gas and suffocated/burned the lungs of the groundhogs. This gas can do the same to people and to use it would be exceptionally risky if not downright stupid.
There are many available insect baits that all work well. Some of these are liquids that illustrate one of the main drawbacks of poisoned baits. The ones that look like honey have appeared enticing to children and they end up getting poisoned instead. This is the main draw back of poison; it is less specific than aiming a gun and can kill things you don't intend to such as domestic animals, beneficial insects and humans.