198 LIFE AND HER CHILDREN. 
leads them to the most curious expedients for holding 
their own in the world. 
But as in other classes, so here too we may be 
sure that lower kinds are filling nooks and corners 
left by their more advanced relations, and our 
history of the spider family will not be complete 
unless we cast a glance at the tiny insignificant 
mites and ticks, which swarm on the land and in 
the water, and live chiefly on the bodies of other 
animals. 
These curious little creatures live that double life, 
which we shall find afterwards in the true insects ; 
for while young spiders are born like the mother, 
and only grow larger as they cast their skins, the 
mites run about for some time on six legs only, an-d 
then hiding themselves in some crack in the ground 
lie motionless for many days, and then come out 
with eight legs as minute spiders, only that their 
body is not divided, but is all one round mass, and 
they breathe by means of curious air-tubes like the 
true insects. 
It is these tiny creatures which destroy the 
leaves of our trees, by burrowing into them and 
sucking the liquid sap, leaving little yellow and 
faded blotches wherever they have been. Some- 
times you may find a leaf with a fine, almost invisible, 
web spread over its under surface, and there you 
may be sure that a complete colony of mites are 
feeding, and bringing up their little larvae or young 
ones, which, when the leaves fall to the ground will 
hide themselves under stones or in the earth, and 
come out perfect mites to take to fresh trees and 
form new colonies. Whenever you see the leaves 
