insects and their world 



The sawflies have no 'wasp waist' at the base of the abdomen (Fig. 57), 

 and get their name from the ovipositor of the female, which may be 

 toothed Hke a saw, and is used' for penetrating the stems and leaves of 

 plants. 



The larvae of sawflies are generally like caterpillars, and feed on vege- 

 tation in the same way : an example is the Gooseberry Sawfly, well known 

 to gardeners. They are distinguished from the caterpillars of Lepidoptera 

 by having more prolegs on the abdomen, and in particular by having a 

 pair on the second segment. 



This group also includes the giant 'wood-wasps', or 'horntails' (Sirici- 

 dae), which have an exceptionally long and thin ovipositor. This is used 

 to pierce the wood of living trees, and to lay an egg within the timber. 

 The larvae of the Siricidae burrow in the wood, and may do great damage. 



The Sub-order Apocrita again divides into two sections, the parasitic 

 groups, and the ' aculeate ', or stinging groups. The parasitic Hymenoptera 

 {Parasitica) (Figs. 59, 63) lay their eggs in some place where the larva, 

 when it hatches, can at once begin to feed on, or in, a living insect. Some 

 choose mainly the eggs of other insects, others the larva, or the pupae, or 

 more rarely the adult. When the parasitic larva feeds on another parasitic 

 insect it is called a hyperparasite. In each case, the parasitic larva is so 

 adapted that it gets as much food as it needs before the host insect is 

 killed. The gall-wasps (Cynipoidea) are in effect parasites of plants, and 

 the irritation set up by their larvae leads to the formation by the plant of 

 swellings called galls. 



The Aculeata (Figs. 60-62) are the bees, wasps and ants, some of 

 which are notorious for their power to sting. This is confined to the 

 female in which the pointed ovipositor has been modified into an organ 

 for attack and defence, which can often discharge a toxic fluid into the 

 wound that it makes. Some ants which cannot sting will bite with their 

 jaws, and then turn round and squirt formic acid from the tip of the 

 abdomen into the wound. Wasps and ants normally have chewing mouth- 

 parts, and use them for feeding as well as weapons against their enemies. 



Bees have the mouthparts drawn out into a long, tongue-like organ 

 (Fig. 25e), with which they suck nectar from flowers, but they still have 

 mandibles. The leaf-cutting bees, for example, leave clear evidence of 

 their chewing powers. 



The larvae of aculeate Hymenoptera are quite helpless, and are sup- 

 plied with food by their parents. Some solitary bees and wasps lay their 

 eggs in holes in the ground, or in wood, provision them with a supply of 

 honey (bees) or insect prey (wasps), and then seal them and leave them 

 alone. On the other hand, the truly social bees and wasps, and all the ants, 

 live in highly organised nests, with perhaps thousands of individuals, each 

 of whom performs a particular set of duties. Social life in insects is dis- 

 cussed in more detail in Chapter VI. 



Certain parasitic species, known as cuckoo bees, and cuckoo wasps, lay 

 their eggs in the nests of other species. 



22 



