Houseflies - Park's Textbook of Preventive and Social Medicine

Introduction

• Musca domestica (common housefly)
• M. vicinia
• M. nebulo
• M. sorbens

Houseflies should be regarded as a sign of insanitation, and their number as an index of that insanitation.

General Characters

(1) Head

• Bears a pair of antennae, a pair of large compound eyes, and a retractile proboscis (adapted for sucking liquid foods).
• In males, the eyes are close together; in females, they are set widely apart.

(2) Thorax

• Marked with 2 to 4 dark longitudinal stripes - characteristic of the genus Musca.
• Bears one pair of wings and three pairs of legs.
• Each leg has a pair of pads (enabling walking on polished surfaces).
• Legs and body are covered with tenent hairs which secrete a sticky substance - important in disease transmission.

(3) Abdomen

• Segmented and shows light and dark markings.

Life History (Complete Metamorphosis)

(1) Egg

• Female lays 120 to 150 eggs at one sitting in moist decaying organic matter (human/animal excreta, manure heaps, garbage, vegetable refuse).
• Indian M. domestica and M. vicinia breed profusely in human excreta.
• Eggs are pearly-white, about 1 mm long, visible to the naked eye.
• Total eggs in lifetime: 600 to 900.
• Hatching time: 8 to 24 hours; in summer in India, may hatch within 3 hours.

(2) Larva (Maggot)

• Measures 1 to 2 mm at birth; full-grown larva up to 12 mm.
• White, segmented, footless with a narrow anterior end and broad posterior end.
• Eat voraciously; moult twice during development.
• Resent light - bury themselves under manure heaps.
• When about to pupate, they migrate to dry outer regions.
• Larval period: 2 to 7 days (prolonged in cold weather).

(3) Pupa

• Dark-brown, barrel-shaped, measuring about one-quarter of an inch.
• Pupal stage in tropics: 3 to 6 days (considerably prolonged in winter).

(4) Adult

• Complete life cycle (egg to adult): 5 to 6 days in summer in India; 8 to 20 days at other times.
• Lifespan: not longer than 15 days in summer and 25 days in winter.

Habits

Transmission of Disease

• Typhoid and paratyphoid fevers
• Diarrhoeas and dysenteries
• Cholera and gastroenteritis
• Amoebiasis
• Helminthic infestations
• Poliomyelitis
• Conjunctivitis and trachoma
• Anthrax, yaws

Mechanisms of Transmission

• Flies transport microorganisms on their feet and hairy legs (tenent hairs).
• Pathogenic organisms, ova, and cysts have been recovered from the bodies of houseflies.
• Hence called "porters of infection".

• The regurgitated stomach contents ("vomit drop") is a rich bacterial culture.
• By frequent vomiting on food, the fly transmits disease.

• Excrement contains numerous microorganisms as well as cysts and ova of intestinal parasites.
• Constant defecation spreads these organisms onto food.

Fly Control Measures

1. Environmental Control (Most Important)

1. Store garbage, kitchen wastes in bins with tight lids pending disposal.
2. Efficient collection, removal, and disposal by incineration, composting, or sanitary landfill.
3. Provision of sanitary latrines (pit privies, septic tanks, water-seal latrines).
4. Stop open-air defecation.
5. Sanitary disposal of animal excreta.
6. Step up general sanitation.

A clean house with clean surroundings is the best answer to the fly problem.

2. Insecticidal Control

Note on resistance: M. domestica first showed resistance to DDT in 1948, and has since developed resistance to organo-chlorine, organophosphorus, and carbamate pesticides.

Insecticides, at best, are only a supplement - not a substitute for sanitation.

3. Fly Papers

• Sticky fly papers are useful adjuncts.
• Made by mixing 2 lbs resin + 1 pint castor oil (heated together), smeared on paper.
• Only a slight, non-lasting reduction in fly numbers.

4. Protection Against Flies (Screening)

• Screening of houses, hospitals, food markets, restaurants.
• Screens with 14 meshes to the inch keep out houseflies.
• Finer screens also exclude other insects.
• Expensive but effective.

5. Health Education

• Fly control without public cooperation is difficult.
• A "fly consciousness" should be created through health education.
• Fly control campaigns require organized individual and community effort.

• Park's Textbook of Preventive and Social Medicine, pp. 876-877