I live in the city and go running daily. On occasion, by the time I arrive back home, I begin itching and realize that I've been attacked be what appears to be a gang of some sort of parasite. The result are a dozen or so welts, mostly on my face and torso which stop itching after an hour or so and are completely gone in a few days. There is no sign of them in my clothing. I've only had two experiences with such parasites- the mosquito and bedbug... long story short, I know from experience that this is neither. What could these parasites be?