IMPORTANT CLASSES OF INSECTS 203 
this order is the plant lice. They have a life history that 
is quite unusual. During the summer they are born alive 
like higher animals and in this way multiply 
with great rapidity, but in the fall a few eggs 
are laid that are preserved over the winter 
and from these the next summer’s crop starts. 
They are minute creatures which live by suck- 
ing the sap from the leaves and tender stems, 
and thus they reduce the vitality of the plants 
and sometimes kill them. They are usually 
found in flocks huddled close together. Some 
have wings and others are wingless. 
To this order also belong the famous 17-year 
‘locusts. It is remarkable that only this one 
species of the 300,000 or more should live 
so long, while all the others live from only 
a few days to not more than three years — 
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Squash Buc 
(Magnified. ) 
An example of 
a true bug. 
comparatively 
few species more than a year. The larval stage, which is 
spent underground, usually lasts 16 years, and in the spring 
Natural size. 
Adult winged female. 
Prant Lice 
Wingless larval 
female. 
or early summer of the 17th year the creatures come to the 
surface and change to the adult form. Soon these adults 
lay their eggs, and the young, after hatching, 
burrow in the 
