Destroying, castrating or spaying animals

[Donny]

There are several facets to your question. One facet is the prohibition of cruelty to animals; another facet is "baal tashchis," the prohibition of destroying (wasting) something.

For Gentiles, a Torah prohibition of cruelty to animals applies only when the person actively causes the animal pain or torment ... if one was to actively kill an animal not for the use of its hide or flesh, etc., but just for the sake of killing it to put it out of its misery with no material benefit to a human, then one has transgressed on being wasteful by destroying one of G-d's creations wantonly.

What about pests (i.e. flies, mosquitoes, ants, mice, etc.)? I had a fly get into my house and now there are quite a few. I've been trying to shoo them out a window, which has worked well, but there are still more in the morning. Can a Noahide kill them with a flyswatter or rolled up newspaper or should (s)he use insecticides or flypaper?

Thanks,
Donny