166 



ENTOMOLOGY. 



closely resemble caterpillars, having from six to eight pairs of 

 abdominal legs (in Lyda there are no abdomi- 

 nal legs, but a pair of singular, jointed terminal 

 appendages); they are usually of some shade of 

 green, and usually moult four times. Most of 

 the larva? secrete silk and spin a dense, tough 

 cocoon within which the half-formed pupa re- 

 sides through the winter, finishing its change 

 into the pupa state in the spring. With its saw- 

 like ovipositor the saw-fly punctures twigs and 

 leaves; as in the case of the larch saw-fly (Nema- 

 tus erichsonii Hartig), the two sets of serrated 

 blades of the ovipositor are thrust obliquely into 

 the shoot by a sawing movement; the lower set 

 of blades is most active, sliding in and out 

 alternately, the general motion of each set of 

 blades being like that of a back-saw. The 

 species of Lophyrus have pectinated antenna?, 

 and are destructive to coniferous trees. 



The pear slug-worm (Selandria cerasi Peck) 

 and the currant saw-fly (Nematus ventricosus 

 Klug) deposit their eggs in rows on the under 

 side of the leaves, and there are successive broods 

 of worms throughout the summer, the females of 

 this species being agamous. The largest of our 

 saw-flies is Cimbex americana Leach, whose an- 

 tennae are knobbed at the end; while its larva 

 as it lies coiled up on a leaf resembles a helix 

 shell. 



Family Uroceridae. The species differ from those of the preceding 

 family in the long, large, exserted borer, adapted for 

 boring into solid wood, and in the fore tibiae having but 

 one apical spur. The larvse are called horn-tails, and 

 bore in pine or hard-wood trees; they are without ab- 

 dominal feet, and when about to transform spin thin 

 silken cocoons. The species of Cephus bore in the 

 stems of wheat, etc., while Tremex columba Linn, infests 

 elm, maple, and other shade trees, making large, smooth 

 round holes in the tree. 



Family Cynipidae. The gall-flies are all of small size, 

 the head generally small and transverse, witli slender, 

 straight, 13-16- jointed antennae; the thorax is usually 

 thick, oval, with a large scutellum, and the wings (some- 

 times wanting) are without a complete costal vein and 

 stigma, and there are few veins; the abdomen is short, 

 generally oval, more or less compressed, rarely knife- 

 shaped; the second or third segment is the largest, 

 while the ovipositor is spiral and concealed within two 

 sheaths. The larva is a short, thick, fleshy, footless 

 grub; and those of many species transform within their 

 galls, or enter the earth to pupate. 



The egg is deposited in leaves or branches, especially 

 of the oak, rose, vacciuium. etc. Its presence, with pos- 



FIG. 208. Pear slug- 

 worm (a enlarged), 

 and its saw-fly. 



FIG. 209. 

 Horn tail : 

 larva of 

 Tremex co- 

 lumba. 

 Nat. size. 



