We usually don't have any but on Saturday I had the window open all day as it was lovely and warm and I noticed Quite a few of them on the inside of the window maybe 10-15 which was a little unusual as we generally have maybe one or two.
Didn't think much of it got rid of them and put it down to having the window open.
I was out from morning until about 6pm last night and came back to at least a hundred on the same window on the inside !!! 