Vector Control CommitteePredominant Flies
Jason Phillippe of San Bernardino County EHS:
“The two predominant flies that are typically the cause of nuisance conditions are Musca domestica and Fannia canicularis. The former is larger and tends to land on food and other surfaces. It is more of a problem in warmer months as opposed to cooler months. It is also called the common house fly. Their larvae (maggots) are typically what you would see in your trash can if you didn’t take out your trash for a while. The latter is smaller and tends to circle (hover) in shaded protected areas such as porches or garages. It is more of a problem in early spring and late fall when temps are cooler. It is commonly called the lesser house fly. Their larvae are brown and move much slower than domestica larvae and to the untrained eye are more difficult to detect.”
- Musca domestica, also known as the common house fly, is found all over the world.
- Adult insects are grey to black with four dark lines on the thorax, slightly hairy bodies and a single pair of membranous wings. They have red eyes and the female is slightly larger than the male. Adult house flies grow to .5 in long.
- The female house fly usually only mates once and lays batches of about 100 eggs on decaying organic matter such as garbage, carrion or feces. These soon hatch into legless white maggots which after 2 to 5 days of development transform into reddish-brown pupae, about 8 mm long.
- The house fly overwinters in either the larval or pupal stage under manure piles or in other protected locations. Warm summer conditions are generally optimum for the development of the house fly, and it can complete its life cycle in as little as seven to ten days. However, under suboptimal conditions the life cycle may require up to two months.
- Adult flies normally live for 2 to 4 weeks but can hibernate during the winter.
- The adults feed on a variety of liquid besides solid materials which have been softened by saliva.
- They carry pathogens on their bodies and in their feces and can contaminate food and contribute to the transfer of food-borne illnesses. For these reasons they are considered pests.
- Fannia canicularis, also known as the lesser house fly or little house fly is smaller than the common house fly, and is spread worldwide.
- It is best known for its habit of entering buildings and circling near the center of rooms.
- The lesser house fly is slender, and the median vein in the wing is straight.
- Larvae feed on all manner of decaying organic matter, including carrion.
- Females lay their eggs in batches of up to 50 and may lay up to 2,000 eggs altogether.
- The eggs, which are white, can float in liquid and semiliquid decaying organic matter, especially poultry, cow and dog feces, kitchen waste such as the end of putrid potatoes or carrots, compost, cheese, bacon and fish. They are commonly found in garbage depots, wheelie bins, garbage trucks, and other places where food waste is stored. The eggs hatch after only 48 hours, and the larvae require six or more days to reach pupation, which lasts seven or more days, so it usually takes about 2-4 weeks to develop into adults, depending upon temperature. The cycle repeats in very damp, putrid excrement, liquid manure, etc.
- The lesser house fly has a life expectancy of two to three weeks. Because they are often found on excrement and human food, they are considered possible disease carriers.
- From May to October, the lesser house fly comes into buildings and is noticeable by its peculiar, silent flight in the room center, where it circles down-hanging articles, particularly lamps.
- It changes the flight direction jerkily. This is a patrol flight, in which the males supervise and attack intruders. During breaks and in the night hours, the flies sit on lamps or on walls and leave their small excrement marks.