We had some flying critters in our loft space you could see them entering from the upstairs window. JG Pest control visited and sprayed the entrance, this curtailed them for a while, but when checking from the loft they were still flying around, the documentation suggested it could take upto 3 weeks. We waited but it wasn't improving so we called them back, on this occasion they released a spray (bomb) in the loft which killed all of them we waited another couple of weeks before investigating further and this seems to have sorted it. I'd recomend them and would use them in the future if needed.