226 INJURIOUS AND USEFUL INSECTS 



the Ichneumons, make a kind of transition to the bees, wasps, 

 fossorial or digging Hymenoptera, and ants, which constitute 

 the aculeate or stinging Hymenoptera. We can roughly 

 picture the relations of the different families by putting the 

 wood-borers and saw-flies in the middle, and grouping the rest 

 outside according to our notions of their aflfinities. 



The Families of Hymenoptera 



Hymenoptera are divisible into three sub-orders : — (i) Sessi- 

 liventres, with sessile abdomen ; (2) Parasitica, with petiolate 

 (stalked) abdomen, but no sting ; (3) Aculeata, with petiolate 

 abdomen and sting (usually). If the sting should be wanting, 

 an aculeate form can generally be recognised by having the 

 trochanter undivided ; it is nearly always two-jointed in the 

 Parasitica. 



Sub-order I. — Sessiliventres 



Family Siricidae (wood-wasps or horn-tails). The female 

 has a long ovipositor, which projects externally. The tro- 

 chanter is two-jointed. The larvae live in the wood of trees 

 (see Lesson 21). 



Family Tenthredinidae (saw-flies). The female is usually 

 furnished with a pair of saws, which are employed in egg-laying. 

 The trochanter of the hind leg is double. The larva often 

 superficially resembles a Lepidopterous caterpillar, but has 

 usually more numerous prolegs; there is always one on the 

 second abdominal segment of a saw-fliy larva, if it has prolegs 

 at all ; while a Lepidopterous caterpillar never has prolegs on 

 that segment. 



The gooseberry saw-fly (see Lesson 20) is a familiar example 

 of Tenthredinidae. 



The pine saw-fly {Lophyrus pint) does great damage in the 

 larval stage to pine-woods. The male fly is only about 6 mm. 

 long, but the wings are relatively long; the antennae are 

 pectinate on both sides; the body is black, but part of the 

 legs is yellow. The female fly is larger by a third, and pale 

 yellow, with black on the head, thorax, and centre of the 

 abdomen. The larva may be 25 mm. (i in.) long; it has 

 eleven pairs of feet, and is greenish - yellow, with darker 

 spots along the sides. The eggs are laid in spring on the 



