25 
laid in irregular masses, often as many as a hundred together, and 
usually hidden in crevices of the bark of trees. 
The female comes out of the ground to lay her eggs from 
February to April, the date varying with the latitude and the sea- 
son. The young caterpillars appear about the time that the apple- 
tree unfolds its leaves, commonly, in this state, in April or early 
May, and they usually get their growth in about a month from the 
time when they issue from the eggs. They then go into the ground 
to a depth of two to five inches, each one in a small cell, where 
they change to the chrysalis, remaining there until the following 
' ^ '- '\^kS^^' 
Fig. 23. Common Canker-worm , PaZracnVa 
ernaia: a, adult male; 6, female; c, portion 
f female antenna; d, joint of abdomen, en- 
arged; e, ovipositor. 
Fig. 24. Common Canker- 
worm, Paleacrita vernata: a, 
larva; b, cluster of eggs, nat- 
ural size, with one enlarged; c, 
side view of one of the seg- 
ments, d, back view of same, 
both enlarged. 
winter or early spring, when the change to the adult insect takes 
place. There is thus but a single generation produced each year. 
The canker-worm is widely distributed thruout the country and 
may occur in destructive numbers in any part of Illinois. Its feeble 
power of locomotion prevents its rapid spread in any locality, but 
by concentration of its injuries it is the more destructive where it 
does occur. 
In its injurious or caterpillar stage (Fig. 24, a) it is readily 
recognized. It has a long and slender form and the habit of a 
"looper'' or measuring worm. When not eating it usually adheres 
only by its hinder prolegs, extending the body from this point of 
support at an angle of about 45 degrees. As it is colored much like 
the bark of a tree, it then has the appearance of a stubbed twig. It 
also has the habit of spinning down from the tree at the end of a 
thread, particularly if the branch is jarred or shaken. Both the just- 
mentioned habits are doubtless advantageous to it ; the first by con- 
cealing it to some degree from the observation of birds and the 
second by putting it beyond their reach. The full-grown canker- 
worm is about nine-tenths of an inch in length and may vary from 
greenish-yellow or gray to dusky or even dark brown, with paler 
stripes along the sides. A close examination will show also two 
light lines running close together along the middle of the back. 
