We used them last year and just received our second shipment for this year. We use them in and around the barn and feed areas and also around the manure piles. We try to move out all the manure in March and April and start with the Predators at the end of April. We thought it made a difference and that's why we tried them again this year. I agree with Chap, get them out early and get ahead of the problem, also get the lots and the barns cleaned out to reduce areas to lay eggs and it will help. Good luck.