If he's doing it so often maybe there won't be so many dead bugs at once. I think that is where the danger is. I once sprayed a tree that was just full of bugs and they were falling off in hoards. To my dismay a pretty brown thrasher I had been seeing every day began scarfing them up. I couldn't run her away. I never saw her again and I think the poisoned bugs killed her. I never used pesticide like that again. I felt so bad. I think generally after it dries it doesn't harm wildlife but if they're in the spray that's different. I don't know what it may do to butterflies that drink from sprayed flowers