High Quality Content by WIKIPEDIA articles! The Blandford fly (Simulium posticatum) is a species of black fly, a biting insect found locally around Blandford Forum and villages bordering the River Stour in Dorset, England. Its larvae breed in the weedbeds of the slow flowing river and when the fly emerges, the female seeks a blood meal before mating. It usually bites the lower legs causing pain and swelling, after which secondary infections set in.