198 INJURIOUS AND USEFUL INSECTS 



of wings, ceases to be a necessity for such insects. 

 Parthenogenesis occurs occasionally (silk -moth, etc.) or 

 normally in some moths (Psychidse). The larva is nearly 

 always a vegetable feeder, and is adapted by its form, colour, 

 the structure of its legs and mouth-parts to a sedentary life on 

 green plants. Exceptional adaptations to life in water, in the 

 trunks of trees, in the combs of bees, etc. are known. The 

 mandibles are the only mouth-parts which are directly con- 

 cerned in feeding during the larval stage. The larva usually 

 moults four times. As the time of pupation approaches it 

 often conceals itself, and may make use of its power of 

 spinning silk to form a cocoon, either composed of silk only, 

 or of silk interwoven with the larval hairs, or leaves woven 

 together, etc. The pupa or chrysalis may be described as an 

 imperfectly developed moth or butterfly covered by a thin 

 pupa-skin, and having its limbs cemented down by a viscid 

 secretion which flows from the body, and hardens on exposure 

 to the air. The proboscis, legs, and wings are tolerably com- 

 plete externally, but imperfectly organised within. Neverthe- 

 less the insect, at the time of pupation and before the secretion 

 is poured out, has often a certain power of moving its limbs. 

 Afterwards they lose more or less the power of movement, but 

 some can wriggle out of holes in the earth or galleries in the 

 trunks of trees, so as to reach the air before the moth emerges. 

 In these movements they are aided by spines or rows of spines 

 attached to the abdomen. Many Lepidoptera pass the winter 

 as pupae, some as larvae, a few as torpid winged insects, many 

 enclosed in the eggs. 



The Families of Lepidoptera 



The classification here adopted is only provisional, but will 

 be of some use in placing butterflies and moths. The arrange- 

 ment of the families on natural lines is still very incomplete, 

 and much too difficult a study for beginners. 



BUTTERFLIES (Rhopalocera) 



Antenna clubbed. Wing's more or less erected when at 

 rest. Body slender. 



The only butterflies of much practical importance are the 

 cabbage whites (see Lesson 15). 



