Hymenoptera 



271 



are laid. The saw is protected by two flaps which are conspicuous 

 at the tail-end of the body. The larva which feeds within the stem is 

 a white, fleshy grub (fig. 149 a, b, c) with mere vestiges of thoracic legs. 

 Only 100 species of this family are known ; they are distributed over 

 Europe, North Africa and North America, and occur in Japan. Cephtis 

 pijgmaeus (fig 149 e) is well-known as injurious to wheat. 



Siricidae. — The Sirkida; are fairly large insects, usually brightly 

 coloured. The front lobe of the mesoscutum is not separated by the 

 lateral lobes from the meso- 

 scutellum. The pronotum 

 though large dorsally is not 

 free from the rest of the 

 thorax. The first abdominal 

 tergite is divided centrally by 

 a small oblong membrane. 

 The hind-body is long and 

 cylindrical, ending in a very 

 prominent spine in the 

 female. She is provided 

 with a very perfect boring 

 ovipositor enabling her to lay 

 eggs in the wood of trees, 

 wherein the large white 

 fleshy grub with mere 

 vestiges of thoracic legs and 

 a stout tail-spine lives and 

 feeds. Only about 100 species 

 of SiricidK are known ; they 

 are characteristic of the 

 northern forest regions. 



Tenthredinidae. — The 



TenthredinidiX or SawFLIES are 

 distinguished from the pre- 

 ceding families by the side 

 lobes of the mesoscutum (fig. 

 i8^j separating the central 

 lobe (e) from the meso- 

 scutellum (^). The p r o - 

 notum is relatively small and 

 closely fused with the meso- 

 thorax. The Sawflies are mostly insects of moderate size. The 

 feelers are very variable; the number of segments is usually nine, but 

 tiiere may be as few as three or as many as forty ; usually they are 

 thread-like, but sometimes feathered. The fore-shin bears two spines. 

 The hind-body of the female is provided with an ovipositor consisting 

 of thin paired plates with the inner edge toothed to act as a saw and 

 the outer face roughened to serve as a file ; these saws are protected 

 by a pair of sheaths. By means of them the female makes cuts in 



Fig. 149. — . 

 magnified 



Corn Saw-fly (Ce/'hiis 

 Curt.), Europe. Female, 

 times ; a. outline of larva, 

 natural size ; l>. larva, magnified ; c. larva 

 in stem, natural size;y. Ichneumon fly 

 {Pachyiiierns calcitrator), whose grub 

 feeds on the larva of the Cephus, magni- 

 fied. From Riley (after Curtis), Insect 

 Life, vol. 2 (U.S. Dept. .\gr.). 



