Fly Identification: Which Fly Is in Your House?

• Crane fly (often mistaken for a giant mosquito): distinguished from mosquitoes by larger size and by wings that lack the scales found on mosquito wings; it is a true fly with only two functional wings.
• Crane flies are harmless — many adults lack mouthparts entirely and they do not bite or sting people.
• Fruit fly (vinegar fly): tiny (~1/8 inch), tan front body with black rear, usually red eyes; found around rotting/fermenting food in kitchens, restaurants, and supermarkets.
• House flies cannot bite because of their sponging mouthparts, whereas some other flies (e.g., stable flies) do bite.

People most often mix flies up with:

• Mosquitoes

Open the other page and compare its list against the marks above; the differences are usually in the antennae, wings or the way the body is divided.

Most common house flies cannot bite (sponging mouthparts); some other fly species, such as stable flies, do bite and feed on blood. Seek medical care promptly for severe symptoms or any allergic reaction.

Fruit flies are common in homes, restaurants, supermarkets, and wherever food is allowed to rot or ferment; they breed in drains, garbage disposals, empty bottles/cans, trash containers, mops, and cleaning rags.

Get as close as your camera will focus, from directly above, in daylight or a bright lamp. Include the whole body with the legs and antennae in frame; a second shot from the side shows wings and body segments. Put a coin or ruler next to it for scale. For a bite or a bug found on skin or bedding, photograph the bug itself, not the mark. The app names the likely group; use the list above to confirm.

• Around the fruit bowl, trash or drains: fruit flies. About 1/8 inch, usually with red eyes, a tan front half and a black rear half; a female lays about 500 eggs and the life cycle can finish in about a week (University of Kentucky).
• Around potted plants and nearby windows: fungus gnats. 1/16 to 1/8 inch, dark and delicate like tiny mosquitoes, with long legs and antennae longer than the head; many species have a Y-shaped wing vein, and they are weak fliers that stay near plants (UC IPM).
• On bathroom walls near a sink, shower or floor drain: drain flies (moth flies). Furry bodies, wings held roof-like, weak fliers that crawl on walls; they breed in sewage, dirty bins, bird baths, clogged gutters and drains (Steve's Pest Control).
• In sunny windows in autumn or in the attic: cluster flies, which gather in compact clusters to overwinter in wall voids, soffits and attics and come indoors as the weather cools (Steve's Pest Control).
• Around garbage or pet waste, shiny green or blue: blow flies, metallic green or blue, often mixed with copper (UC IPM).
• Grey, anywhere indoors: house flies, under 3/8 inch, with four dark stripes on the back of the thorax (UC IPM).
• Smaller swarms outside near compost or manure: little house flies, about two-thirds the size of a house fly, breeding in poultry manure, fermenting grass and compost (UC IPM).
• A house-fly-sized fly that bites outdoors: stable fly, with a bayonet-like mouthpart sticking out in front of the head; it breeds in moist rotting plant material mixed with manure, such as old grass clippings (UC IPM).
• Large biting flies near water or livestock: horse flies; see horsefly bites.
• A long-legged "giant mosquito" on the wall: crane fly, which is harmless (see above) and compared with mosquitoes.

UC IPM says eliminating the places where larvae develop is the preferred way to control pest flies, so finding the source matters more than killing adults.

• Drains and garbage disposals: tape a clear plastic food storage bag over the opening overnight; if flies are breeding inside, adults emerge into the bag (University of Kentucky).
• Potted plants: push raw potato chunks, cut side down, into the soil to draw out fungus gnat larvae, or stand small squares of yellow sticky trap on skewers in the pots to catch adults (UC IPM). Larvae can leave slime trails on the soil surface like tiny snail trails.
• Kitchens: fruit flies breed in ripe or rotting produce, drains, disposals, empty bottles and cans, bins, mops and cleaning rags (University of Kentucky).
• Outdoors: seal garbage in plastic bags, have it collected weekly and wash bins regularly to stop blow flies; remove old grass clippings and turn compost to stop stable flies (UC IPM).

Flies are two-winged insects: the University of Kentucky notes the hind pair of wings is reduced to a small balancing organ shaped like a golf tee, which is the quickest way to rule out bees and wasps. To go further, a photo needs a clear view of the wings (vein pattern and any spots), the eyes and the back of the thorax, ideally from above and the side. Some flies are hard to name even for experts: the NatureSpot gallery marks each species red, amber or green by how easy it is to identify. InsectIdentification.org notes that flies and mosquitoes together number over 20,000 known species in North America. Photograph it and InsectLens identifies it.