Fenestil do a roll on that you can keep in you pocket this is quiet good for Blackfly bites. Also I picked up a clicker device in Aldi last year for 1.5 Euro. Zap it, it sends a small spark between two terminals when applied to a bite, I thought it was a gimmick but I swear by it now, never go anywhere without it. I was terrified of the Blackfly bites because of the allergic reaction, I once used a full tube of Fenestil in one night now I do not give them a thought.  :)