8 BULLETIN 1238, U. S. DEPARTMENT OF AGRICULTURE 



ECONOMIC IMPORTANCE. 



During periods of abundance enormous damage is done by one or 

 the other species of cankerworm, or by both working together. When 

 especially abundant, the larvae defoliate the trees, leaving only the 

 midribs and larger veins of the leaves with a few ragged shreds of 



Fig. 2. — Distribution of the spring cankerworm. 



leaf tissue. (PL I, A, C.) When the worms are somewhat less 

 abundant, the leaves may not be entirely consumed, but many of them 

 turn brown and dry. In either case, the trees are badly weakened, 

 and, if defoliated for several years in succession, are likely to be 

 killed. Young orchards not in bearing, which are often not tho- 

 oughly sprayed, neglected orchards, and unprotected shade trees 



