There are a large variety of species of bottle and blow flies. Adults are up to 5/8 inch long and usually a bright metallic green, blue, or bronze, but they may be black. Mature larvae are 3/8 to 7/8 inch long, creamy white, and tapered at the head end with a visible black mouth hook. These flies may appear suddenly and in large numbers.

Adult female flies of most species lay batches of dozens to hundreds of eggs in suitable larval food materials, such as animal carcasses, excrement, and sewage. They will feed on decaying plant matter, such as rotting lawn clippings, when meat is not available. Larvae hatch within hours under the best conditions and feed on, then burrow into, the food source. They pupate beneath the food source or just below the soil surface, often emerging in huge numbers at once.

Bottle and blow flies are filth flies. They have sponging mouthparts and must regurgitate on solid food to partially digest it for consumption. Since these flies visit feces and are usually the first to show up at carcasses, they are significant vectors of illness, carrying up to 100 different disease organisms on and within their bodies. These flies are a nuisance pest to people outside and will venture indoors when warmth or odors attract them. Indoors, particularly in restaurants, bottle and blow flies can be a major sanitation issue. Bottle flies are also known to be a major group responsible for myiasis, or the infestation of tissues or cavities by fly larvae. Ironically, one species of green bottle fly is used in medical wound healing known as maggot therapy, where sterile maggots are introduced into a nonhealing wound. The maggots feed only on dead tissue and bacteria, leaving living tissues intact and reducing infection quickly. Maggots secrete bacteria-destroying compounds that kill even antibiotic-resistant bacteria.