24 
THE STUD Y OF INSECTS. 
Spiders make use of silk in the construction of their 
webs or snares, in the building of tubes or tents within 
which they live, in the formation of egg-sacs, and in loco¬ 
motion. 
Fig. 23 represents the large egg-sac of one of the orb- 
weavers. This is made in the autumn, and contains at that 
season a large number of eggs—five hun¬ 
dred or more. These eggs hatch early in 
the winter; but no spiders emerge from 
the egg-sac until the following spring. If 
e gg-sacs of this kind be opened at differ¬ 
ent times during the winter, as was done 
by Dr. Wilder, the spiders will be found 
to increase in size but diminish in num¬ 
ber as the season advances. In fact, a 
strange tragedy goes on within these 
egg-sacs: the stronger spiders calmly 
devour their weaker brothers, and in 
the spring those which survive emerge 
sufficiently nourished to fight their bat¬ 
tles in the outside world. 
The egg-sacs of the different species of spiders vary 
Fig. 23.— Egg-sac of 
A rgiope riparia, 
(From Wilder.) 
Fig. 24.— Egg-sac of Nephila plum!pcs (From Wilder.) 
greatly in form. In some, as in that figured above, the outer 
covering is very dense, while in others the outer part con- 
