Hornets !
Last couple of nights at work I have seen a couple of huge (I thought wasps) in the offices. It is one of those hermetically sealed buildings with no opening windows so was a bit puzzled. Went in last night to find my floor had been abandoned early afternoon and extermination was taking place because they found a huge nest in the roof space and apparently lots of hornets had invaded the offices just after lunch!
Never seen wasps or bees about so early so was quite surprised hornets were active.