I.] METAMORPHOSES OF INSECTS. 23 



on leaves, not directly on the plant itself, but attached 

 to it by a long white slender footstalk. The larva 

 has six legs and powerful jaws, and makes itself 

 very useful in destroying the Hop-fly. 



The insects forming the order Trichoptera are well 

 known in their larval condition, under the name of 

 caddis worms. These larvae are not altogether unlike 

 caterpillars in form, but they live in water which is . 

 the case with very' few lepidopterous. larvae and form 

 for themselves cylindrical cases or tubes, built up of 

 sand, little stones, bits of stick, leaves, or even shells. 

 They generally feed on vegetable substances, but will 

 also attack minute freshwater animals. When full 

 grown, the larva fastens its case to a stone, the stem 

 of a plant, or some other fixed substance, and closes 

 the two ends with an open grating of silken threads, 

 so as to admit the free access of water, while excluding 

 enemies. It then turns into a pupa, which bears 

 some resemblance to the perfect insect, " except that 

 the antennae, palpi, wings, and legs are shorter, en- 

 closed in separate sheaths, and arranged upon the 

 breast." The pupa remains quiet in the tube until 

 nearly ready to emerge, when it comes to the surface, 

 and in some cases creeps out of the water. It is 

 not therefore so completely motionless as the pupae of 

 Lepidoptera. 



The Diptera, or Flies, comprise insects with two 

 wings only, the hinder pair being represented by 

 minute club-shaped organs called " halteres." Flies 

 quit the egg generally in the form of fat, fleshy, 

 legless grubs. They feed principally on decaying 

 animal or vegetable matter, and are no doubt useful 



