412 ANNUAL REPORT SMITHSONIAJS INSTITUTION, 1921. 



caterpillars; but the tents of this species do not inclose leaves and 

 are used only for shelter, the occupants going out in bands to forage 

 on the leaves of the trees, returning home to rest after each meal. 

 In some parts of the country, particularly in New England, the fall 

 webworm is commonly known as the " bagworm," but it is improperly 

 so called because this name belongs to another caterpillar, one more 

 abundant farther south and more properly deserving of the name 

 since it encases its body in a close-fitting bag. 



The fall webworm belongs to the family Arctiidae, which includes 

 also such well known caterpillars as the brown and yellow woolly 

 bears and the hedgehog caterpillar. The last is that popular weather 

 prophet who is supposed to have his brown and black colors pro- 

 portioned each fall according to the weather prospects of the com- 

 ing winter. Most of the Arctiid caterpillars are hairy or woolly 

 and have the hairs grouped on tubercles of the skin. They run with 

 that characteristic humping motion noted especially in the later 

 stages of the webworms. The moths are of medium size but most 

 of them have strikingly beautiful colors, the wings being white, 

 yellow, brown or red, and spotted or banded in a great variety of 

 patterns. For this reason they have been given the general name 

 of tiger moths. Some of them, however, are of plain colors. The 

 moths of the fall webworms are usually pure white, though some 

 have the front wings covered with small brown or blackish spots 

 and the abdomen brownish above (fig. 11), while an occasional in- 

 dividual has a few spots on the hind wings. The spotted ones are 

 usually males, though some females also are spotted. The back of 

 the thorax and the head are clothed in long soft fur, the large black 

 eyes stand out prominently on the sides of the face, while below 

 each eye are two small tufts of blackish hairs. The antennae are 

 usuallv white above, dark brown beneath, with the brown encroach- 

 ing on the sides of the segments and producing a spotted effect, but 

 often the upper surface is brown also though the fringe may be 

 white, The bases of the front legs and parts of the middle legs are 

 pale sulphur yellow. The tibiae and feet usually are blackish on 

 their front edges except at the ends of the joints, which gives them 

 the appearance of being ringed with white. The wings expand 

 from 1^ to If inches and when closed the body and wings are five to 

 seven eighths of an inch long. 



The fall webworm ranges all over the eastern part of the United 

 States from the Atlantic coast to the Rocky Mountains, and also 

 lives in parts of California. It feeds on a great variety of deciduous 

 trees, 120 species being listed in its known diet as given in Bulletin 

 10 of the U. S. Bureau of Entomology. It is particularly a pest in 

 orchards and on city shade trees. Trees kept sprayed with arseni- 

 cals are of course freed from webw T orms along with other leaf-feed- 



