222 LIFE AND HER CHILDREN. 
need to hide it in some strong covering. And for 
this purpose they build themselves tubes of silk, into 
which they weave pieces of wood and grass, or of 
sand and stone, and even sometimes shells with living 
creatures in them; and dragging these tubes about with 
them, they put out their strong head and shoulders, 
and feed on plants and insects. Then when the time 
comes for their change they draw back into their case, 
and closing it with a grating of silk at each end, so 
that water can get in while enemies are shut out, 
they lie still for a fortnight, like a caterpillar in its 
chrysalis, and then swim out and creeping up some 
plant burst their covering skin, and hover over the 
pond, or rest upon the bushes till their eggs are laid, 
ahd they die. 
Thus, the May-fly and Caddis-fly live chiefly in 
the water, finding plenty of food during all their 
growing time, while they have but a short glimpse 
of the pleasures of the air. Not so, however, the 
gorgeous-winged Dragon-fly. He manages to make 
the most of both worlds, and, whether he is crawling 
in the water below, or flying in the air above, is one 
of the most voracious and bloodthirsty of insects. 
Even when he is a water-grub, though he moves 
very slowly, yet the quickest of insects cannot escape 
from him, for he has a peculiar under lip (m, Fig. 7 6), 
very long and with two sharp hooks at its broad 
end, with which he seizes them. This lip folds back 
by a kind of hinge, and is called a mask, because 
it covers the lower part of his face, and makes 
him look an innocent and harmless creature. The 
moment an insect comes by, the lip is shot out, and 
the pincers grasp the prey, throwing it into his mouth 
