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ANNUAL REPORT SMITHSONIAN INSTITUTION, 1924 



common to many other measuring worms and in its origin perhaps 

 was beneficial. A habit more clearly protective is that which the 

 caterpillars possess of letting themselves drop suddenly at the ends 

 of threads from their spinnerets when a branch on which they are 

 feeding is lightly jarred, and of hanging suspended in midair. After 



Fig. 9. — Spring cankerworms in various tittltudes on twigs of apple trees 



a time, when no danger seems to threaten, they ascend their threads 

 and resume feeding. 



The cankerworms feed on several species of trees, but their favorite 

 kinds are apple and elm. Wherever the worms have fed on apple 

 leaves the scars become bordered by reddish brown areas, which, 

 spreading over the uneaten parts, give the leaves the scorched appear- 



