22 



EXTERNAL STRUCTURE OF INSECTS 



Order Diptera ("two-winged"). These are the true flies, such 

 as the house-fly, mosquito, horse flies, etc., characterized by the 

 possession of only two wings, the second pair being represented by 

 a pair of small knobbed projections, the halteres or balancers; they 

 have mouth parts adapted for sucking, lapping or stabbing. They 

 have a complete metamorphosis, the larva being referred to as a 

 " maggot," and the pupa or resting stage is enclosed in a brown 

 skin called puparium. Figure 27 illustrates a type of the order. 



Order Siphonaptera. These are wingless, degraded insects, 

 with no compound eyes, but having a complete metamorphosis. 

 The mouth parts are adapted for sucking. Here occur the dog and 

 cat flea, human flea, and others. 



FIG. 26. A true bug. 



FIG. 27. House-fly on lump of sugar. 

 (After Brues.) 



Order Lepidoptera ("scale-winged"). The butterflies, moths 

 and skippers are characterized by the presence of four wings, cov- 

 ered with tiny scales which easily rub off if the insect is handled 

 roughly. To these minute scales is due the color of the wings. 

 The mouth parts of these insects are modified for sucking. They 

 have a complete metamorphosis. The larva is spoken of as a 

 "caterpillar," and tent caterpillars and cut- worms are familiar 

 objects in the country. Caterpillars have six true legs, and a 

 varying number of temporary fleshy projections called "pro-legs," 

 or "prop-legs." The moths are generally, but not always, night 

 fliers; their antennae are usually either thread-like or feather-like. 

 When at rest they rarely hold their wings elevated as do butter- 

 flies. The skippers are day fliers, and dart rapidly from place to 



