158 THE SCREW-WORM. 
THE SCREW-WORM. 
(Campsomyia (Lucilia) macellaria Fab.). 
This fly is a flesh-fly with the additional bad habit of 
being very impatient, as it does not always wait until the 
animal is dead that is to furnish the food for the offspring. 
As a general rule, it lives, like all its relatives, upon decaying 
animal and vegetable matter in and about which it under- 
goes allits transformations. The eggs, about one-sixteenth 
of an inch long, of a light yellow color, are deposited by the 
female on or near dead animals. The mother must possess 
wonderful organs of smell, or of some other sense, which en- 
able her to detect such food, even if well hidden or obscured 
by other odors. These eggs being quite soft, would soon be 
destroyed by the direct rays of the sun, hence they are de- 
posited under the carcass, or on its shady side. Such flies 
are known to contain as many as 20,000 eggs in their 
ovaries. These eggs hatch in one or two days, depending 
upon the length of the time that they were retained in the 
ovaries by the mother-fly before discovering the proper food 
for her young. The dirty-white larva possesses the usual 
form of fly-maggots; a ring of bristles between each pair of 
segments gives the maggot a fancied resemblance to a screw, 
hence the above popular name. These bristles act as legs in 
locomotion. The mature maggot is three-fourths of an inch 
in length, and about one-eighth of an inch in diameter; it 
possesses a tapering head, that contains two pointed black 
hooks, which are the mouth-parts used to obtain food. The 
posterior end of the maggot is very much truncated. The 
maggots grow very rapidly and reach their full size in four 
to six days, when they leave the substance upon which they 
have fed and enter the ground, where, just below the surface, 
they contract into dark-reddish and barrel-shaped puparia, 
about one-third of an inch in length. Insidesucha puparium 
the fly is formed, which takes about 7 days, when it leaves 
both the puparium and the ground to fly about and enjoy 
life according to its peculiar fashion. This fly (mane 
plate XI) is a very beautiful insect, a little larger than our 
common house-fly, of a bright metallic green color, and hav- 
ing prominent dull-red eyes; its back is marked with three 
