2978 



THE JOINTED ANIMALS 



STEM SAWFLIES Family 



The larvae of these slender, delicate, armored insects pass their lives in the 

 stems of plants or young shoots of trees; and the adults are characterized by the 

 saw of the female being partially concealed by two integumental flaps. As an 

 example of the typical genus, we may take the corn sawfly ( Cephus pygmczus) , of 

 which the perfect insect flies actively in the sunshine, flitting from blossom to blos- 

 som among buttercups in May, and thence onward through the summer. The 

 larvae cause serious damage on the Continent to rye crops, and more rarely in wheat 

 fields, where they crawl up and down within the stems, feeding on the delicate 

 tissues. When full fed, they construct a transparent cocoon in which to pass the 

 winter, becoming pupae, and a little later in May emerging as full-grown sawflies. 

 The parasitic insect (Pachymerus calcitrator) figured in the illustration on p. 2977 is 

 one of the Petiolate Hymenoptera which seems to be exclusively parasitic on the 

 present species. 



TAILED WASPS Family SlRICID^E 



In this family the female is furnished with a long, boring ovipositor for 

 piercing the bark of trees; the eggs being laid in the orifice thus formed, and the 



larvae feeding on the wood. In the accompanying illus- 

 tration of the boring apparatus of one species c, c, a, shows 

 the whole of the muscular structure with which the boring 

 is carried out. The perfect insects .are usually of large 

 size and conspicuously colored. Among the typical forms 

 the common tailed wasp (Sirex juvencus) is a very rare 

 species in England, although more plentiful on the Conti- 

 nent. The females, which are sometimes surprised in the 

 act of depositing their eggs on pine trees, may be easily 

 caught, as the ovipositor can only be withdrawn with con- 

 siderable difficulty. Indeed, the abdomen breaks in half, if 

 the insect be roughly grasped. The much larger giant-tailed 

 wasp (S. gigas) is far commoner among pine trees, and is 

 distinguished by its bands of black and yellow. Although 

 it does considerable damage, it does not attack a perfectly 

 healthy tree, unless recently felled. How long the larvae 

 may live in the interior of the tree, and how long it is 

 before the perfect insect appears, is not known, but cases 

 are often quoted of this insect appearing in houses soon after 

 their completion, having evidently emerged from the wood 

 of the joists and beams. Another genus is well repre- 

 sented by the broad-bodied sawfly (Lyda campestris). 

 In this species the grubs feed on the young shoots of the 

 Scotch fir, in which the eggs are laid. When hatched, the larvae spin a slight 

 web in which they remain concealed, protruding the fore part of the body 



BORING APPARATUS OF 

 GIANT-TAILED WASP. 



(Much enlarged.) 



