LEPIDOPTERA 429 



the type usually found in insects which masticate their food: in 

 Micropteryx there is no proboscis, the animal feeding on pollen; in 

 Eriocrania the mandibles are non- dentate, the laciniae are lost and 

 the galeae form a short proboscis. 



The characteristic feature of the wings is the clothing of scales 

 (Fig. 317). These latter are formed by enlarged hypodermal cells, 

 and their main function appears to be the presentation of colour due 

 either to the pigment they contain (like the uric acid of the Pieridae) 

 or to striation of the surface causing interference colours. There also 

 occur "scent scales" which may have a sexual significance. Several 

 methods of wing coupling have been developed independently in the 

 order. The commonest consists of a stout bristle or frenulum of the 

 hind wing locking into a retinaculum composed of curved setae on 

 the fore wing. 



In the females of certain Lepidoptera the wings are totally lost and 

 the animals are confined to the food plant on which they spend their 

 larval life. The male is attracted to the female, under these circum- 

 stances, by scent. 



Lepidopterous larvae (Fig. 322 A-C) have three thoracic and ten 

 abdominal segments with nine pairs of spiracles situated on the pro- 

 thorax and first eight abdominal segments. The mandibles are typi- 

 cally strong and dentate ; the maxillae are stumpy and consist of a 

 cardo, stipes and single maxillary lobe with a two- or three-jointed 

 palp: the labium has a large mentum, a prementum bearing a 

 median spinneret and small two-jointed palps. 



The thorax bears three pairs of legs, and the abdomen five pairs of 

 pro legs on segments 3-6 and 10. These are different from the typical 

 insect limbs, being conical and retractile with hooks on the apex 

 (Fig. 322 C). In many families there are less than five pairs of prolegs, 

 and in Micropteryx there are eight pairs. 



These larvae feed almost exclusively on flowering plants (exceptions 

 being the Lycaenid caterpillars which are carnivorous, feeding on 

 aphides or entering ants' nests and devouring the larvae). Their 

 digestive enzymes are modified for dealing with plant tissues. 



Lepidoptera are almost invariably harmful in the larval stage, few 

 plants being free from their attacks, and some of the world's most 

 serious insect pests, such as the cotton boll worm, Platyhedragossypiella, 

 and the gypsy moth, Porthetria dispar, are included in this order. 



Order COLEOPTERA (Beetles) 



Biting mouth parts ; fore wings modified to form horny elytra which 

 meet along the mid-dorsal line; hind wings membranous — folded 

 beneath the elytra — often reduced or absent; prothorax large and 



