472 THE INSECT WORLD. 
in such a manner that the animal seems to be clothed in pearls. Tt 
is thus the air reaches the spiracles. The female of the Hydrophilus 
is sometimes seen clinging to aquatic plants, head downwards, 
forming her cocoon, terminated by a long pedicle, in which she 
places her eggs, by means of the two bristles situated at the 
extremity of the abdomen (Fig. 471). After having drawn this 
after her for some time, she leaves it to itself in calm water. At 
the end of a fortnight, there come out from it little brown larve, 
very active, which ascend the water plants. These larvz are at 
the same time herbivorous and carnivorous. They live on plants 
and smal! molluscs, which they seize from underneath, and whose 
shell they break by pressing them against their back, to extract 

Fig. 471.—Bristles at the extremity of the Fig. 472.—Pupa of the Hyd@rophilus. 
abdomen of the Hydrophilus. 
from it the animal. If attacked, they emit a black liquid, which 
discolours the water, and enables them to escape. At the end of 
two months, the larva comes out of the water, and burrows into 
the ground to undergo its metamorphosis into a pupa (Fig. 472), 
which becomes a perfect insect a month afterwards. The latter 
gets its colour little by little, and comes out of the ground at the 
end of twelve days. According to M. Dumeril, the intestine of 
the larva grows gradually longer and longer, as its diet becomes 
that of herbs, the adult preferring vegetable food to animal 
matter. It is at the end of summer that the Hydrophilus piceus 
becomes perfect, and it passes the winter in a state of torpor at 
the bottom of the water. The females lay in the month of April. 
