THE CANKERWORMS 29 



dated June 7, 1826, Koland Howard (7) relates that after a period 

 of abundance from 1806 to 1809, practically no worms were present 

 in 1810, which was attributed by some to a severe storm soon after the 

 worms had hatched. It seems likely that either cold, stormy weather, 

 or extreme cold unaccompanied by rain, especially if this occurs soon 

 after the larvae have hatched, may be fatal to them. 



Wet weather also favors the development of wilt diseases, but these 

 do not seem to have been at any time prevalent enough to account for 

 the sudden disappearance of the cankerworms. 



DISEASES. 



Peck noted that some of the larvae were attacked by a disease which 

 he called " deliquium," evidently referring to one of the wilt diseases 

 which commonly attack lepidopterous larvae. Wellhouse (36) re- 

 cords finding a wilt disease killing some larvae of the spring canker- 

 worm in Kansas. Sherman (39) , reporting on a severe outbreak of 

 the fall species in the mountains of North Carolina, which had been 

 in progress for four seasons, stated that fungous and bacterial dis- 

 eases were not much in evidence " although warm and damp weather 

 was not lacking. Only an occasional worm was found which seemed 

 to have perished from disease- and there was no hint of an epidemic 

 among them." Under crowded conditions and in the confined air of 

 some of the rearing cages used for miscellaneous material in the 

 insectary at Wallingford, a very few larvae were attacked by some 

 form of " wilt " disease, but no infected larvae were found under field 

 conditions. The cankerworms do not seem to be as subject to wilt 

 diseases as are many caterpillars, especially the colonial forms. 



STARVATION. 



In a letter to the Western Rural of June 23, 1866, Sanford Howard 

 (i#), secretary of the Michigan Board of Agriculture, suggested 

 among other things that the cankerworm may have been present in 

 such numbers that the available foliage was not sufficient to carry 

 them to maturity. It seems entirely conceivable that under certain 

 conditions the larvae might be numerous enough to exhaust all avail- 

 able foliage by the time they were only partially grown. In such 

 a case very few larvae would be successful in reaching maturity, and 

 the infestation would be greatly reduced the following season. Nat- 

 urally, starvation in this manner could occur only where the canker- 

 worms were exceptionally abundant. 



BIRDS. 



Because the cankerworm larvae feed in exposed locations, and are 

 not protected by hairs or other repellent devices, they are a favorite 

 food with many of our common birds. Work done by Forbes (22) 

 in Illinois indicated that when the cankerworms became unusually 

 abundant, many different species of birds ate enormous numbers of 

 them. Chickadees have been found with large numbers of the eggs 

 of the fall cankerworms in their crops (28) . Even specimens of the 

 much-despised English sparrow have been found with their crops 

 full of cankerworm larvae. Practically all of our common birds 

 have been recorded at one time or another as cankerworm feeders, 



