206 GEOLOGICAL SURVEY OF NEW JERSEY. 



convert a certain amount of it into caterpillar tissue, and their 

 work is done. Little impress is left upon the tree under ordinary 

 conditions, or unless the feeding numbers are excessive. Even 

 if one of the large species defoliates a branch, this is not serious 

 except on conifers, which, on the whole, suffer less from attacks 

 of this kind. 



The larvae of saw-flies are also feeders upon forest-tree foliage, 

 and these sometimes do local injury. Saw-flies are Hymenoptera, 

 i. e., they belong with the bees, wasps and ants in structure ; but 

 they differ by having the abdomen closely joined to the body, not 

 connected with it by a slender waist. Saw-fly larvae resemble 

 caterpillars in shape and appearance ; but have at least 18 legs, 

 instead of 16, as in true caterpillars. They have a tendency to 

 feed in colonies and often curl up the end of the body when feed- 

 ing at the edge of a leaf. A black-spotted species occurs on pine, 

 sometimes in such numbers as to attract attention and defoliate 

 even large branches. Small or ornamental trees in parks are 

 sometimes killed or severely injured ; but on larger trees a dead 

 twig or small branch is the extent of the mischief caused. 



Some of these larvae are covered with a white powdery bloom, 

 and at least one species, occurring on willow, becomes of con- 

 siderable size, reaching an inch and a half in length when 

 extended at full length. It is pale yellowish in general color, 

 with a whitish, small head and a black stripe down the back, 

 making it easily recognizable and a fair sample of this kind of 

 larva except in size. 



On the hickory and butternut other species occur that are 

 known as "woolly worms," because of the masses of fine waxen 

 threads that cover the body and give it a fluffy appearance. 



Yet other species are gall-makers, causing blister or marble- 

 like excrescenses on leaves, stems or twigs, in the center of which 

 the larvae feed. Willows and poplars are especially subject to 

 this kind of attack. 



Among the caterpillars, besides those that eat of the leaf-tissue 

 directly, many are leaf miners, eating between the upper and 

 lower surfaces, sometimes irregular blotches, sometimes galleries 

 of definite form, each species having a constant and character- 

 istic type. A few others make little cases or sacks, in which 

 they live and which they carry about with them. Many are leaf- 



