DIP TER A. 
415 
larval skin. A few are enclosed in cocoons. When the 
pupa state is passed within the last larval skin the body of 
the pupa separates from the larval skin more or less com¬ 
pletely; but the larval skin is not broken till the adult fly 
is ready to emerge. In this case the larval skin, which 
serves as a cocoon, is termed a pupariuni (pu-pa'ri-um). In 
some families the puparium retains the form of the larva; 
in others the body of the 
larva shortens, assuming a 
more or less barrel-shaped 
form (Fig. 483, 2), before 
the change to a pupa takes 
place. 
This is a large order, 
both in number of species 
and individuals. The spe¬ 
cies differ much in habits. 
Some are very annoying to 
man. Familiar examples 
are the mosquito, which 
attacks his person ; the 
flesh-flies, which infest his 
food ; the bot-flies and gad¬ 
flies that torment his cat¬ 
tle ; and the gall-gnats that 
destroy his crops. Other 
species are very beneficial. 
Those belonging to the 
Syrphidae, and to the sub¬ 
family Tachininas of the 
Muscidae destroy many noxious insects; and very many 
species, while in the larval state, feed upon decaying animal 
and vegetable matter, thus acting as scavengers. 
Although the habits of these creatures, which revel in 
all kinds of filth, are very disgusting, we cannot help admir¬ 
ing that arrangement by which a mass of filth, instead of 
Fig. 483.—The Apple-maggot; i. larva; 2, pupa¬ 
rium; 3, adult; 1a, head of larva from side, 
showing mouth-parts and cephalic spiracle ; 
ib, head of larva from below ; ic, caudal 
spiracle of larva. 
