The heat hits, windows sit ajar and suddenly your kitchen fills with big black flies bouncing off the glass and circling the bin. Invasion of big black flies: why swatting them is almost pointlessMost of these visitors are the common house fly, Musca domestica, around 5 to 8 mm long but looking chunky and black as they buzz your kitchen. House flies have large compound eyes with a wide field of view, excellent motion detection, and sensory hairs and bristles that can detect air movement. Gilbert also points out that "When someone tries to swat a house fly, the fly usually reacts by launching away from the approaching object. When you see a cloud of big black flies inside, it usually means there is one or more breeding spot nearby.