You likely do not wanted to trap your ermine / weasels, believe me. They feed primarily on rodents, especially mice, and if you have a lot of them it's because you also have a lot of rodents.
A good friend is a trapper, and had a lot of Ermine around his place. He trapped a bunch, and says, "Last time I'll do that! Used to have weasels, now I have mice the size of weasels!". Anywhere with a high weasel population, there's a reason... and the weasels are a lot friendlier to have around, some people here try and encourage weasels to hang around.