ORDER HYMENOPTERA 293 



better to look upon it as an independent development of a 

 similar structure based on similar habit. The number of 

 prolegs varies from twelve to sixteen. There are twenty-two 

 legs altogether. The saw fly larvae become fully grown by 

 the latter part of the summer and secrete themselves near 

 the surface of the ground, generally among dead leaves and 

 rubbish. They spin a quite strong silken cocoon w^ith a 

 papery texture, somewhat more dense than is common for the 

 caterpillars of the silk-making moths. In this cocoon they 

 remain as larvae for quite a period. They finally pupate and 

 the adults issue in the spring and deposit eggs so as to 

 produce the summer generation of willow worms. They 

 become of economic importance where the shade trees they 

 feed upon are of importance — willow trees, elm, etc. They 

 are parasitized and the cocoons are eaten by mice and so 

 kept down generally to a moderate number and are not 

 usually very destructive. 



The pear slug (Eriocampoides limacina) occurs quite 

 commonly in orchards and attacks not only the pear, from 

 which it dervies its name, but also apple and other orchard 

 trees. The larva has a strict resemblance to the mollusks 

 called slugs, as the body is covered with a dense slimy secre- 

 tion which hides the segmentation and external features of 

 the body. They feed upon the surface of the leaves, just 

 leaving ribs and veins. The trees attacked often have the 

 appearance of being scorched by fire. 



They are best treated by the application of arsenical solu- 

 tions, applied as soon as their work appears. 



The American rose slug {Endelomyia rosce) is frequently 

 troublesome in its attacks on the leaves of rose bushes which 

 are stripped or skeletonized so that the bushes are rendered 

 quite unsightly. 



Arsenical solutions can be used, or if these are not desired, 

 hellebore may be used for their control. Other species 

 affect gooseberry, strawberry and other such crops. Many 

 instances being of considerable importance. 



The Uroceridoe are wood- or stem-boring species and 

 more specialized than most of the preceding family. 



