222 INJURIOUS AND USEFUL INSECTS 



the surface of the wood. They generally belong to the 

 Rhynchophora, and either to the family Scolytidae (Scolytus, 

 Hylesinus), or to that of Curculionidse (Hylobius, Fissodes). 

 A few beetles of other groups {Agrilus, Molorchus, etc.) 

 make burrows beneath bark, but are less important as 

 destroyers of standing trees. 



HYMENOPTERA 



Structural peculiarities. — The head is usually furnished, 

 especially in the male, with large compound eyes, three 

 pairs of simple eyes, and long antennae which can be 

 moved briskly. The waist is usually narrowed for greater 

 flexibility, but there is a section of the order with sessile 

 abdomen. The wings are membranous, narrowed at the 

 base, with few radiating veins, and usually connected during 

 flight by a row of hooks on the fore edge of the hind wing, 

 which catch a fold or rim on the margin of the fore wing, 

 and so keep the web extended. In large Hymenoptera 

 there are expansions of the air-tubes in the abdomen, which 

 increase the buoyancy of the insect. In ants the workers 

 are wingless, and the fertilised females lose the wings 

 previously used for flight. The mouth-parts are primarily 

 adapted for biting, but may become suctorial as well, by 

 the prolongation of a kind of tongue (see p. 84). The females 

 are nearly always provided with an ovipositor, for laying 

 the eggs in narrow spaces. The ovipositor may be con- 

 verted into a saw, a borer, or a sting, all of which are present 

 in females only. 



Winged Hymenoptera are often brightly coloured, and in 

 the stinging families black and gold are frequent colours. 

 Bands of black and gold, with clear wings, rapidly vibrated, 

 and the habit of poising over flowers in the sun, will give 

 to any insect the appearance of a wasp or bee, and this 

 fact is taken advantage of by flies, moths, bugs, and beetles, 

 certain species of which mimic (of course, unconsciously) 

 the widely known and dreaded stinging Hymenoptera. 



The ovipositors of insects. — The last segments of the 

 abdomen are often modified for purposes of reproduction 

 in both male and female insects. We shall here shortly 

 consider some of the special forms which these segments 



