Can you enlighten me on this. Several years ago we were playing racket and ball games in the garden the light was fading and suddenly there were loads of flying insects coming through the grass. The noise was deafening and they flew straight in to the trees. They were quite large a bit like a small bumble bee but dark brown. I can't remember the time of year. I ran into the house but Mic was battering them with his racket. Any ideas?