I have noticed this. I did a backpack trip in the Winds and while I was bitten by mosquitoes, there were very few welts and they vanished within about a day with very minimal itching. On Sunday I went for a hike in the mountains above Santa Barbara and at least two groups of people complained to me about all the flies and how horrible they were. I never noticed a single fly. Usually they have quite a knack of flying into my eyes or ears.
Female, 5'3", 49, Starting weight: 163lbs. Current weight: 135 (more or less).
Starting squat: 45lbs. Current squat: 160 x 2