Interesting. Though, I have to wonder...if fly spit does such a good job of healing wounds, why don't fly bites heal quickly?!
They take big bites?
By fly bites, do you mean the raised itchy bumps like you get? I think they form as an immune response to the protein, rather than as a direct result of the bite. A bump such as that could persist long after the actual wound is sealed.
My experience with these nasty guys is one of coming away with much worse injuries from them as compared to mosquitos. Black flies, and many other biting flies, use more of a laceration method than the syringe-like mosquitos. Here's a site that does a much better job of describing it than I.
From above site:
The resulting swelling and itch is a histamine-based reaction to proteins in saliva- anticoagulants, etc., potentially exacerbated by the fact that the wound heals faster and doesn't flush out the affected area.
Separate names with a comma.