Read this article to learn about the Structure and Life Cycle of the Housefly !
The housefly (Musca domestica) is the most common of all domestic flies. The body of housefly is distinguished into head, thorax and abdomen. The head is hemispherical in shape and bears two lateral compound eyes. Three simple eyes (ocelli) are also present on dorsal side of the head. Two small and mobile antennae are present in the head region. The thorax is formed of three segments prothorax, mesothorax and metathorax. Each thoracic segment bears a pair of lateral legs. Mesothorax bears a pair of wings and prothorax bears a pair of spiracles, close to the wings (fig. 8.9).
The abdomen is made up of ten segments. The first remains undeveloped; the second and 6-10 segments are very small. Segments 3-5 are normal. In females these segments form ovipositor to help in reproduction. In the males, the last abdominal segment serves as an external genitalia and the 9th segment bears a pair of claspers for copulation. The abdomen bears spiracles for respiration in both males and females. The last segment bears anal cerci in both males and females.
The mouthparts of housefly are of ‘sponging type’ i.e. these are adapted for sucking liquid or semi-liquid food like a sponge.
Life cycle of Housefly:
Houseflies copulate in summers and rainy season during March to October, but most frequently during August and September.
Four to five days after copulation, the female fly starts laying fertilized ova (eggs). Eggs are laid in small clusters inside semisolid decaying matter such as dung, horse manure, human excreta, decaying fruits and vegetables etc., about a centimeter deep from the surface. About 100 to 150 eggs are laid at a time. About 500 to 600 eggs are laid by a single female in 4 to 6 installments during its life span of about a month.
Eggs and their hatching:
Eggs of houseflies are shiny white, about 1 mm. long, slightly curved and elliptical in shape, with one end somewhat broader than the other. Each is dorsally marked by two long and curved, rib-like longitudinal thickenings or ridges. Within a short period of 8 to 24 hours a larva develops in each egg and hatches out through a long slit in the egg case (fig. 8.10).
A freshly hatched larva is about 2 mm. long, whit, soft, cylindrical, legless and headless creature called a grub or maggot. Its body is narrow and tapering in front and thicker behind. It is covered by an exoskeleton of thin cuticle. The head is small and thin. It bears a terminal and ventral mouth. A pair of black and hook-like chitinous mandibular sclerites project in front from the rim of the mouth. These help the larva in locomotion, and in tearing solid food particles.
The larval phase is divisible into larval stages called instars. The freshly hatched larva is called the first instar larva. It undergoes first moult within 2 or 3 days and becomes the second instar larva. After a 2 or 3 days’ interval the second moult occurs, and the larva becomes the third instar larva.
In about 3 or 4 days, the third instar larva metamorphoses into altogether a different type of young form called pupa. It is about 6 mm. long. It has no mouth or anus. Hence, it does not feed, but respires through spiracles.
The series of changes that occur during the development of adult from the larva is called metamorphosis. The metamorphosis in housefly involves drastic changes as the young forms of housefly (maggot and pupa) are quite different from the adult.
The freshly liberated imago is colourless. Its wings are small and immobile. Due to exposure to air, the wings soon become hard and fully spread out. Gradually, the normal colour is also attained by the body. In about 15 to 20 days, the new fly itself starts reproducing.
Housefly is a harmful insect as it carries the pathogen of a number of dangerous and infectious diseases of man. The houseflies carry many pathogenic micro-organisms like bacteria, protozoans and their spores. Some very dangerous and even fatal diseases, spread by houseflies are dysentery, anthrax, diarrhoea, typhoid, tuberculosis, cholera etc. Housefly causes myiasis in man; they invade human tissues and lay their eggs in these tissues. The diseases caused by housefly can be managed by preventing houseflies from breeding and disease dissemination.