geez maybe that's what I have! i got this huge itchy red spot ever since my ride last week in the same spot as you! on my thigh, aout two inches below the crotch area on the inner thigh. About where the bike shorts end. And there's a kind of long wiggly line extending out from it...this happened once before on my arm. I didn't even remember getting bitten! totally weird...it never occured to me it was a spider but i think it was!