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The habits of filth flies favor
the spread of bacteria and other disease-causing organisms. Filth
flies often feed and lay eggs on garbage, manure and carrion before
contaminating human foods and food preparation surfaces by landing
on them. When feeding, house flies regurgitate their stomach
contents onto food to liquefy it before ingesting it. They also may
contaminate food and surfaces by defecating on them.
Identification
The order Diptera is composed
of the "true flies," and is one of the largest groups of insects.
Diptera means "two wings." True flies have only two wings (one
pair), instead of the four wings (two pairs) found in most other
types of winged insects. All flies are attracted to moist organic
material upon which they lay their eggs. This habit makes filth
flies valuable as scavengers but also brings them in contact with
humans.
Filth flies can be divided into
two groups, determined by their appearance and food preferences.
Filth flies such as the house fly, blow flies and flesh flies are
relatively small, soft-bodied insects with large eyes. They are
strong fliers. Other filth flies, such as drain flies, fruit flies
and phorid flies, are smaller, with more delicate bodies and legs.
| |
Large filth flies |
Small filth flies |
|
Adult |
stout
bodies
short legs |
slender
bodies
long legs |
|
Larvae |
maggot |
maggot or
worm-like |
|
Food
preferences |
manure,
carrion,
garbage |
drain
sludge, organic debris,
rotting plant material |
Large filth flies
House fly (Musca domestica) -- The
common house fly is a dull gray fly one-fourth-inch long with four
dark stripes on the middle section, or thorax, of its body. House
flies typically lay eggs on animal feces and garbage. White, legless
maggots are the larval stage. They hatch from the eggs and grow to
about one-half inch. When fully grown, maggots crawl away from their
food source to undergo the pupal stage. They form a dark brown
cocoon, known as a puparium, and later emerge as adult house flies,
which can fly one or two miles in search of suitable egg-laying
sites.
Blow flies (Calliphoridae spp.) -- Blow
flies are so-called because the larvae develop inside the bodies of
dead animals, causing the carrion to have a bloated appearance. They
also are attracted to garbage. Blow flies are about the size of
house flies or slightly larger. They have been called bottle flies
because their shiny blue and green color resembles colored glass
bottles, though some species are shiny black or bronze. Large
numbers of these flies indoors usually indicates the presence of a
dead animal such as a mouse or bird inside the structure.
Flesh flies (Sarcophagidae spp.) --
Appropriately named, flesh flies usually seek carrion or scraps of
meat on which to lay their eggs. Like house flies, adult flesh flies
are dark-colored -- gray or black. Common species have three dark
stripes on the thorax. They are slightly larger than house flies and
have a checkerboard pattern on the abdomen.
Stable fly (Stomoxys calcitrans) --
While not always found in filthy situations, stable flies deserve
mention because both sexes feed on the blood of animals, including
humans -- often biting around the ankles. The bites are painful but
are not known to transmit disease to humans. Females lay eggs in
rotting straw and manure, moist piles of animal feed, and yard
waste.
Cluster fly (Pollenia rudis) -- Not
associated with filth, cluster flies are mentioned here because they
are a common household pest. They also resemble house flies but hold
their wings parallel to the body, not in a triangular configuration
as house flies do. Cluster flies are covered with fine golden hairs
and have no stripes on the thorax. These flies are unusual in that
they lay eggs on earthworms. The larvae consume the worms. In the
fall, adult cluster flies often invade homes, especially attics, for
a warm, sheltered spot in which to spend the winter. Unlike other
filth flies, the principal means of controlling cluster flies is
exclusion, that is, sealing buildings to prevent their entry.
Small
filth flies
Fruit flies (Drosophila spp.) -- Also
known as vinegar flies, fruit flies are attracted to sweet or
fermented liquids such as liquor, syrup, soda pop and vinegar, in
addition to ripening and rotting fruit. Females lay eggs in and
around these materials, upon which their tiny larvae feed. The
gnat-sized adults typically have tan-colored bodies and red eyes.
Phorid flies (Phoridae spp.) -- Also
known as humpbacked flies because of their arched thorax, phorids
are tiny, dark-colored flies. The larvae feed on a wide variety of
decomposing organic (of plant or animal origin) debris. If suitable
materials are present, huge populations of phorid flies can build up
quickly. Sources of infestation include liquefied garbage, sewage
and carrion, often hidden in places difficult to inspect and access.
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column in this article] |
Drain flies (Psychodidae spp.) -- About
one-eighth-inch long, adult drain flies are slightly larger than
other small filth flies. Their broad, hairy wings have given rise to
another name: moth fly. They also have been called sewer flies,
because they infest raw sewage. Drain fly adults are often noticed
resting on bathroom walls. The larvae survive submerged in the
gelatinous muck that accumulates in floor, sink and toilet drains by
extending their breathing tubes to the surface for air. To eliminate
infestations, drains and traps should be cleaned with a wire brush
or drain cleaner.
Fungus gnats (Sciaridae and
Fungivoridae spp.) -- Fungus gnats are relatively delicate,
long-legged flies that look like tiny mosquitoes. The larvae of
fungus gnats live in moist places where fungus, their food, grows. Indoor infestations can be associated with pigeon
droppings and with overwatered potted plants where fungi develop.
When removing pigeon or bat droppings, take care to wet the area
first with disinfectant to kill disease-causing organisms that can
be present in the droppings.
Managing filth flies
>
Sanitation
The key to managing all filth flies is
sanitation. Eliminating fly breeding sites -- the material to which
they are attracted to and on which they lay eggs -- is usually
sufficient to eliminate and prevent fly infestations. Conversely,
without thorough sanitation, other control methods are largely
ineffective. Therefore, trash should be kept in sealed containers:
trash bags and cans with tight-fitting lids. Dumpsters should be
kept as clean as possible, emptied regularly and kept as far away
from buildings as is practical. Manure and other decaying plant and
animal material should be promptly removed. Also, eliminate areas of
excessive moisture.
>
Inspection
Just as sanitation is the key to
successful filth fly management, inspection is the key to
sanitation. To eliminate fly breeding sites, one must first locate
the attracting material. Often this can be accomplished only by
conducting a thorough inspection of the premises and by knowing what
to look for and where to look. First identify the flies involved,
inspect for material that attracts that species, and then eliminate
the material.
>
Exclusion
Another important step in fly
management is to exclude them from the premises. This is done by
keeping doors, windows and vents closed as much is practical and by
screening and sealing around these and other fly entry points.
Automatic door closing devices and air curtains that blow air away
from doorways also can be installed to supplement an integrated fly
management program.
>
Mechanical control
In addition to swatting flies,
mechanical fly control includes trapping. Sticky flypaper is one
type of fly trap. Ultraviolet light traps are another, often used to
supplement fly control in commercial buildings. To be effective,
light traps must be properly placed. This type of trap should be
placed where it cannot be seen from outside the building, away from
competing light sources and food preparation areas, and no more than
5 feet above the floor, where most flies fly. Bulbs should be
changed at least once per year.
>
Chemical control
While the use of pesticides is usually
not the best means of managing filth fly problems, sometimes
chemical control can be a valuable component of an integrated fly
management program. Pesticide-releasing fly strips can be placed in
attics and smaller, unoccupied enclosed rooms where filth flies are
a problem. Contact, or non-residual, pesticides labeled for fly
control can be applied as a space treatment ("fogged") to kill adult
flies. This type of control provides only temporary relief, however,
and cannot be relied upon to eliminate the problem. Residual
pesticides -- those that remain active for some time -- can be
applied to outdoor surfaces where flies rest, such as the outside
surfaces of barns, stables, restaurants and houses. Some pesticide
bait formulations are also available for outdoor fly control,
including use around dumpsters.
Note: When pesticides are used, it is
the applicator's legal responsibility to read and follow directions
on the product label. Not following label directions, even if they
conflict with information provided here, is a violation of federal
law.
* * *
This document was published with the
assistance of the University of Illinois Extension. It is available
on the Illinois Department of Public Health website at
http://www.idph.state.il.us/
envhealth/pcfilthflies.htm.
For more
information, contact the Illinois Department of Public Health,
Division of Environmental Health, 525 W. Jefferson St., Springfield,
IL 62761; phone (217) 782-5830 or TTY (800) 547-0466, for
hearing-impaired use only.
[Illinois
Department of Public Health
news release]
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