Insects and their world 



males may have fully-developed wings : an example of this is the Spring 

 Cankerworm, the wingless females of which climb the trunks of trees to 

 lay eggSj and against which greasebanding is used. 



Except for the family Micropterygidae — the members of which have 

 chewing mouthparts, and are excluded from Lepidoptera by some authori- 

 ties — most adult Lepidoptera have a proboscis that is adapted for sucking 

 liquid food. Occasionally the proboscis is greatly reduced, and no food is 

 taken. We always think of butterflies as feeding delicately from the nectar 

 of flowers, but they also like rotting fruit, wounded and sappy trees, 

 perspiration, stagnant water, and so on. 



The larvae of Lepidoptera are caterpillars, and feed on vegetation. They 

 are distinguished from the caterpillar-like larvae of Mecoptera and of 

 sawflies (Hymenoptera-Symphyta) by having six spot-like ocelli on each 

 side of the head, and by the fact that the abdomen never has more than 

 five pairs of prolegs, which are equipped with crochets (small hooks). 

 Caterpillars have chewing mouthparts, and eat great quantities of vege- 

 tation, so that many of them are agricultural and horticultural pests. 



When caterpillars are ready to pupate, they often spin silk from modi- 

 fied salivary glands. This may be used to support the pupa during its 

 resting stage, or to build a protective case, or cocoon. The silk worm, 

 Bomhyx mori, is a caterpillar that feeds on mulberry leaves, and spins 

 enough silk in its cocoon to be commercially profitable. 



26. Diptera (North America 16,700; world 85,000) 



Flies (Figs. 43-47, 49-50, 52-54, 72). Many different groups of insects 

 are called 'flies': dragonflies, mayflies, ichneumon flies, and so on. The 

 true flies are an Order distinguished by having only one pair of wings 

 (the fore-wings) complete and ready for flight; the hind-wings are modi- 

 fied into knobbed balancing organs called halteres. 



Besides being very numerous and occurring everywhere, flies have a 

 great range of size and shape. At one end of the Order are the crane-flies 

 (Fig. 43) and midges, either very small, or fragile and long-legged, with 

 long antennae of many segments. These are the Sub-order Nematocera. 

 At the other extreme are the compact, often bristly flies, like the house- 

 flies and bluebottles, fruitflies and dungflies, and so on, which, together 

 with the hoverflies, form the Sub-order Cyclorrhapha (Figs. 49, 52-54)- 

 In between there is a third Sub-order, the Brachycera, which includes 

 such families as the horseflies (Tabanidae) and the robberflies (Asilidae) 

 (Figs. 50, 72). 



The smallest flies may be 1-2 mm. long, and the biggest have a wing- 

 span of 50-75 mm. (2-3 in.). 



All adult flies have sucking mouthparts (Fig. 25c). Many merely mop up 

 liquids with a sort of sponge called the labellum, but others pierce and 

 suck the blood of other insects, or of mammals and birds. Mosquitoes, 

 horseflies and tsetse flies suck blood; robberflies kill other insects. Some 

 families of flies live entirely as parasites on birds and mammals, including 



20 



