Green and blue bottle flies typically indicate the presence of what in a building?

• A. Open drain
• B. Dead animals
• C. Clogged drain
• D. Leaking sewer line

Answer: (B)

Green and blue bottle flies are blowflies that prize decaying flesh. In buildings, their appearance almost always signals a hidden source of carrion, such as a dead animal carcass tucked in walls, in an attic or crawl space, or inside a damaged appliance or pipe area. They don’t camp on decaying matter by chance—their life cycle relies on feeding and breeding in decomposing tissue, so finding them indoors points to a dead animal somewhere nearby.

This differs from drain issues, which would attract different flies that specialize in moist, organic buildup in drains. A leaking sewer line can smell and bring in many pests, but bottle flies specifically indicate carrion, not just a plumbing problem. So spotting them indoors should prompt a search for a concealed dead animal source.