252 



APPLIED ENTOMOLOGY 



twigs or other parts of the plant on which they feed. The female is wingless and 

 lays its eggs within the pupa case or skin she vacated on becoming adult. Only 

 one species, the Common Bag-worm (Thyi-idopteryx ephemercefonnis Haw.) is of 



much importance, but where this is plentiful 

 the plants on which it feeds may suffer con- 

 siderably (Fig. 251). It occurs from Massa- 

 chusetts west to Nebraska and south to North 

 Carolina, Tennessee and Texas. Spraying in- 

 fested trees as soon as the eggs hatch in the 

 spring, with arsenate of lead, standard formula, 

 is usually a sufficient control without a second 

 application later. 



Family Geometridae (Inch worms, 

 Span worms or Measuring worms). — This 

 is a large family in this country and the 

 moths vary greatly in size, some being 

 very small while others may spread nearly 

 two and one-half inches. They nearly all 

 have rather delicate wings and are fragile 

 creatures. 



The larvse (Fig. 252) have a peculiar 

 appearance when moving, as the feet which 

 are usually present near the middle of the 

 body in most caterpillars, are lacking in 

 this group, leaving only the three regular 

 pairs near the front end and two pairs at 

 the hinder end. In consequence, walking 

 is accomplished by bringing the hinder 

 end up as closely as possible to the front 

 end, the body forming at this time a loop. 

 Then the front legs let go their hold and 

 the body is straightened out to find a 

 place where the front legs can grasp and 

 hold on. This striking method of locomo- 

 tion has led to the common names given 

 to the caterpillars in this family. 



Another feature of interest about these 

 larvse is that many of them are colored and 

 formed so as to resemble twigs. When 

 disturbed the caterpillar releases the grasp 

 of its front feet and straightens out, standing at an oblique angle to the 

 twig it is holding on to, and resembles a dead twig of the plant. Some 

 have markings which make them resemble twigs having buds, leaf-scars 

 or scales of the bark, thus increasing their deceptive similarity. 



Fig. 252. — Two "Inch Worm" 

 larvae, the lower one crawling, the 

 upper one hanging outward like a 

 twig. Compare with real twig just 

 above, on opposite side. (From 

 Linville and Kelly, General Zoology.) 



