Omg, Deerflies are the worst!!! DEET works super well with me for mosquitos, and Lemon Eucalyptus helps with mosquitos as well. Unfortunately, DEET has never worked for me and blackflies. So my bug net just came in, and my lemon eucalyptus spray shipped and is enroute...I can't stand the getting bitten all over my ears, and those blackflies always try to get in my eyeballs and my nostrils...I hate hiking in backfly season. But this year I will be ready!!!