Blow flies are a type of “filth fly” recognized by the metallic blue, green, or bronze color of their body. One group of blow flies, the blue bottle flies, are sometimes found inside buildings in the Northeast, appearing suddenly in groups of a few, to dozens at a time. Female blow flies are experts at finding food and will lay eggs on decaying organic material such as dead animals, garbage and feces. Indoors, adult flies are attracted to light and will congregate at bright windows or light fixtures. Because of their feeding behaviors, these flies can carry and transmit pathogens, making them an important public health pest.