Groundhogs are incredibly durable, most attempts to kill them merely end up being torture. Shooting is best. However, I too moved into suburbia and no longer feel comfortable shooting guns near neighbors.
I have tried gassing them with car exhaust to no effect. Drowning works, but it takes an incredibly long time, and you need a container large enough to immerse the entire trap completely, and you need to hold it down as they can swim the whole trap to the surface. If you go this route, be prepared to have the animal struggle for five minutes or more in the most heartbraking fashion. Do it right, and fully immerse the trap in a full garbage can, or what have you and keep it immersed. Incompetance and letting them get a lungful of air, lengthening the suffering is inexcusable. Drowning is a pretty horrible way to die, even for a groundhog, and I wouldn’t do it again. I felt pretty lousy about it.
I know of two ways that work:
-
They don’t take heat well. If it’s a hot summer day, and you put the cage on blacktop, they will expire peacefully in a few hours from the heat. It looks peaceful, but I’m not sure, so I don’t feel to good about this, plus it invites spectators.
-
I have an old golf club that the head fell off. I sharpened the end on a grinder. Put the cage on grass. Stand astride the cage holding the club in both hands. Get the sharp end between the wires from above. Move slowly, until the point is directly above center mass/between the shoulders. The animal will not cooperate, but if you keep moving slowly, or distract it with a third person or by nudging your shoes against the side of the trap, you can get the shank in position. It’s best if you’ve got the groundhog with his face in a corner, rather than backed into a corner of the trap. Don’t hurry, just stay there for a 30 seconds or so and wait for the groundhog to relax a little and take its attention off the stick. Drive down suddenly as hard as you can, and all at once with your full body weight. Do it right, and it’ll be over in about ten seconds, as you impale them to the ground. The trick is not to hold back, but to give it your all. There is a squirmy, nasty second there before you’re all the way through as the groundhog tries to escape. Don’t let up.
My neighbor (we live next to a farming field and have lots of groundhogs) dumps the groundhog from the trap into a big plastic garbage can and then beats them to death by stabbing down with a baseball bat. He’s pretty good at it, but I haven’t tried it, because I’m afraid of the animal coming after me as I’m trying to release the trap, or tipping over the can, so I just shank them through the trap in the manner described. It’s the must humane way I know of.