OUTLINES OF ENTOMOLOGY. 49 



larva3 the surface is smooth and glossy, in others spiny or mossy or cov- 

 ered with a slimy exudation, while others excrete a powdery or cottony 

 substance that gives them a very peculiar appearance. 



Some species, such as the White-pine worm, have the habit of ele- 

 Yating the head and tail when at rest, others keep the body coiled when 

 not feeding, while a few construct leafy cases which they carry about 

 with them or to which they retire for repose. 



A few species are gregarious, feeding in large companies or spin- 

 ning large gummy webs in which they cluster in masses. When full 

 grown many of these larvie drop to the ground and form tough oval 

 cocoons among the fallen leaves and rubbish, or they burrow into the 

 earth and enclose themselves in cells thinly lined with silk. Most spe- 

 cies hibernate in the larva state, without changing to pupte until the 

 following spring. 



The family of the Horn-tails (Urocerid^) contains comparatively 

 few species. They are mostly large insects with stout cylindrical 

 bodies, characterized by a long straight horn extending from the 

 abdomen. In the males this appendage is at the tip, but in the females 

 it arises from the middle of the underside of the abdomen and consti- 

 tutes the ovipositor. It is more auger-like than saw-like in its form and 

 use, and is used for boring into the trunks of trees, especially the elm 

 and pear, to which the boring larvae are often very destructive. 



The wings are narrow but strong, expanding more than two inches, 

 and in flight making a loud buzzing sound. The length of the body 

 including the horn is also more than two inches. 



The species known as the Pigeon Tremex (Tremex cohimba, Linn.) 

 is one of the most injurious. Its multiplication is, however, very 

 much checked by a large ichneumon fly which runs its long ovipositor 

 into the auger-holes of the Tremex, leaving in each one an egg, from 

 which hatches a deadly enemy and devourer of the first Horn-tail larva 

 which it meets. 



