Guide to identifying flies

November 9, 2022

There are over 120 000 species of flies across the world with around 18 000 found in North America. When it comes to New Jersey, the three most common species of flies are the house fly, sewer fly and fruit fly. For some perspective, the female house fly lays up to 600 eggs in her lifetime and flies only live uo 21 days! 


Flies develop through metamorphosis, with the stages of metamorphosis being egg, larval, pupal and adult life stages. When it comes to identifying flies in general, they usually have either two types of mouthparts. Either they have sucking and piercing mouthparts or scissor-like jaws. These flying pests can also be split into two types these being biting flies and filth flies. 


As stated above, there are many species of flies and we have put together a guide to help you identify the most common types. 

Identifying Species of Biting Flies

Deer Flies


  • Usually gray or light brown in color however, some species may have black and yellow stripes
  • Colors are vivid and they have clear wings
  • Adults grow to ¼ or ⅓ inches long
  • Found throughout the United States and are mostly spotted at ponds and marshes as they thrive in dampness
  • Bites are painful as they inject saliva which is made up of an anticoagulant that can cause allergic reactions
  • Carry and transmit diseases and parasites including anthrax, hog cholera, anaplasmosis, tularemia and Lyme disease.


Black Flies


  • Not actually exclusively black in color (as the name suggests), they can also be gray, yellow or brown.
  • Distinctive shiny thorax and humped back
  • Adults are between 1 and 5 mm long 
  • Thrive in moist environments and around flowing water.
  • Can be found throughout the United States
  • Bites can cause skin rashes, swelling and in some cases, a strong allergic reaction




  • Brown, white, black or silver in color
  • Slender and scaly bodies with thin legs and a large proboscis 
  • Adults grow to between 3 and 9 mm long
  • Thrive in hot and humid environments and found across the United States
  • Commonly found near swamps and ponds however, they are also found near any still body of water which is why they are often found in yards
  • Can transmit a variety of diseases including encephalitis, Zika virus, West Nile virus, malaria and Chikungunya virus.


Horse Flies


  • Gray or black in color with bright green eyes
  • Adults are between ½ and 1 ¼ inches long
  • Thrive in moist areas of the United States 
  • Gravitate toward damp and warm areas which is why they are usually found close to lakes, streams and pools
  • Bites are painful and can cause allergic reactions 
  • If bites are left untreated they can cause bacterial infections
  • Can transmit equine infectious anemia, often referred to as swamp fever


Identifying Species of Filth Flies

House Flies


  • Gray with 4 black stripes on the thorax and hair bodies with red eyes with thousands of lenses in each eye, providing a vast range of vision
  • Most common species of flies
  • Adults grow to between ⅛ and ¼ inches 
  • Found across the United States, usually found in humid and warm conditions
  • Feed on trash, feces and decaying food or substances
  • Usually encountered near humans
  • Spread pathogens including conjunctivitis, salmonellosis, tuberculosis, typhoid fever and gastroenteritis.


Drain Flies


  • Also known as sewer flies and moth flies
  • Gray or tan in color with large, hairy wings
  • Between 1 ½ and 5 mm long
  • Found across the United States
  • Thrive near drains and sewers 
  • If they are in in your home this is a sign of a blocked drain
  • Spread bacteria near drains and around kitchen areas
  • Can trigger asthma in sufferers and cause a parasitic infestation of human tissue known as myiasis



  • Also known as bottle flies
  • Range in color from green or blue to black or bronze
  • Shiny bodies
  • Adults grow to between 8 and 10 mm
  • Found across the United States and live in warm, humid environments with low wind
  • Larvae grow inside bodies of deceased animals which means the presence of blow flies indoors may be an indication of a dead animal within your home or business
  • Spread bacteria that can cause bacteria
  • Spread pathogens such as tuberculosis, tularemia and anthrax


Fruit Flies


  • Brown or tan in color with dark or red eyes
  • Grow between 3 or 4 mm long
  • Found anywhere in the United States
  • Found near rotting or ripe fruit and fermented items, mop buckets, drains and garbage disposals
  • Spread bacteria including listeria, salmonella and E.coli


Phorid Flies


  • Usually brown or black in color, while some have a yellow tinge
  • Phorid flies have two nicknames, the first being “humpbacked flies” due to their significantly arched thoraxes and the second being “scuttle flies” due to their erratic behavior
  • Adults grow to between ½ and 5 ½ mm long
  • Located across the United States wherever there is moisture
  • Commonly found near drains, garbage cans, crawl spaces and plumbing
  • They feed on rotting food which allows them to spread bacteria that causes diseases such as conjunctivitis, hepatitis A, gastroenteritis and salmonellosis as well as tuberculosis
  • Infestations can become expensive as they usually develop within plumbing systems which can cause expensive damage
  • Eliminate breeding in plumbing by scrubbing drains with drain cleaner in a foam formant 


If you are struggling with fly infestations or have any questions regarding these annoying insects, call the Twin-Boro experts today.