24 
The spraying of large elms is, of course, a difficult and expen- 
sive operation, and canker-worms are less susceptible to arsenical 
poisons than many other insects. There is, however, a much cheaper 
and more convenient method of protecting the elm, by which ad- 
vantage is taken of two features in the economy of the insect. 
When the caterpillars are full grown they leave the tree to pupate 
in the earth, and the female moth emerging, being wholly without 
wings, can only reach the tree to lay her eggs by cli mining up the 
Pig. 22. Injury to elms at Calamus Lake, Niantic, Illinois, 
by common Canker-worm (Paleacriia vtinata). 
trunk. If this is encircled at the proper time by a sticky band im- 
passable by her or by young canker-worms just hatched from the 
tgg, the tree is virtually secure against canker-worm injury except 
as worms may reach it from neglected trees w'ith which its own 
branches interlace. 
Altho the female canker-worm (Fig. 23, h) is wingless, the 
male (Fig. 2^^, a) has two pairs of rather large, thin, ashy or 
brownish-gray wings, the first pair with a broken whitish band near 
the outer edge and three interrupted brownish lines between that 
and the body. There is also a short oblique black mark near the 
tip of the wing, and a black line at its edge at the base of a fringe 
of hairs. The eggs (Fig. 24, b) are about .03 of an inch long, oval 
in outline, and of a pearly luster at first, changing to yellowish- 
green with a golden, greenish, or purplish iridescence. They are 
