THE INSEC7 WORLD. 



307 



become so, there would be no trouble in protecting the j:)lants 

 by means of the arsenites. 



Now we reach the family Geometridce, in which the larvae lack 

 all save one or at most two pair of false or abdominal legs. In 

 moving they first extend the body to its full length, then bring 

 the posterior end close to the front legs, looping the body in 

 the centre, then stretch out again and repeat the procedure, 

 whereby they have gained the names ' ' span-worms, " " loopers, 

 or "measuring-worms," and, indirectly, the scientific term 

 Geometridae. There is never any difficulty in recognizing the 

 caterpillars, and the moths are easily known in most instances by 

 their slender bodies, small heads, and very broad wings, which 

 are also, as a I'ule, frail and thin. The hind wings are here orna- 

 mented much as are the fore-wings, so that the lines of the one 

 pair are often continued across the other. When at rest, the in- 

 sects keep the wings extended and flat, much as specimens are 

 pinned in the cabinet. We have a large number of species, but 

 comparatively few of them become troublesome. 



Perhaps the best known of all are the " canker-worms," larvae 

 of the species of Anisop- 



teryx and Pakacrita. 

 These attack a consider- 

 able variety of trees, and 

 are especially fond ot 

 apple and pear, which 

 are sometimes completely 

 defoliated. They are 

 much more troublesome 

 in the New England and 

 Northern States, and I 

 have often seen, in Mas- 

 sachusetts, orchards com- 

 pletely defoliated by 

 them. In New Jersey 

 southward they 

 become trouble- 

 Here, as in some 



Fig. 349. 



Fig. 349, Paleaci ita veiiiala. — a, male ; b, fe- 

 male ; c, d, structural details. Fig. 3.S0, Anisop- 

 teryx pometaria. — a, male ; b, female ; c, d, e, 

 structural details. 



and 



rarely 



some. 



of the Bombycids, the sexes are unlike, the males being winged, 



while the females are wingless. The caterpillars, when full- 



