SHADE TREE INSECTS 



13 



Cankerworms 



The Fall Cankerworm, Alsophila ponietaria Harr. 



The Spring Cankerworm, Paleacrita vernata Peck. 

 The cankerworms, also known as measuring or inch w^orms, or sometimes as 

 loopers, attack the leaves of numerous broad-leaved trees in the northeastern 

 United States. They are known to be especially injurious to elms and apples. 

 At various times, elms in different parts of Massachusetts have been severely 

 defoliated by these insects. Both kinds of cankerworms may be found on the 

 same trees. One lays its eggs very late in the fall and is, therefore, called the 

 fall cankerworm; the other lays its eggs very early in the spring and is known 

 as the spring cankerworm. Both hatch at about the same time in the spring, and 

 the >oung caterpillars may be found feeding together soon after the leaves have 

 appeared. 



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Elm Leaves Injured by Cankerworms. 



Description. The two species may be told apart in their various stages by 

 the following characteristics: 



In both species the female moths are wingless. The female of the fall species is 

 uniformly gray, while the spring species has a dark, longitudinal stripe on its 

 back. In both species the male moths are winged and are a brownish gray, the 

 fall species being darker. The adults of both sexes of the spring species have 

 ■on the top of the first seven abdominal segments a transverse row of sharp reddish 

 spines projecting toward the rear. In the fall species this is absent. 



The individual eggs of the fall species are shaped like a flower pot, are flat on 

 top, and fairly smooth on the side; whereas those of the spring species are oval in 

 shape and ridged on the side. 



The caterpillars vary in color and have several thin longitudinal stripes on 



