F. COMMON INSECTS OF OTHER ORDERS 

 33. CADDIS- WORMS AND CADDIS-FLIES (Trichoptera) 



We shall next consider some groups of insects which are 

 not in any important degree either injurious or useful. They 

 are so common as to invite attention, and the most practical 

 of entomologists should at least know what they are, and some 

 little about their life-history. The insects in question occupy 

 Lessons 33-36. 



Among the commonest inhabitants of our ponds and 

 streams are caddis-worms, insect-larvse which make cases to 

 protect themselves against fishes or predatory animals of 

 other kinds, and swim or crawl about, carrying their cases with 

 them. There are many different species, which vary greatly 

 in the sort of case which they construct. Some use gravel 

 or sand, others leaves, sticks, grass-stalks or shells. Whatever 

 the materials, they are fastened together by silken threads, the 

 product of the large salivary glands. The cases differ much 

 in form and size ; they may be straight or curved, open at both 

 ends, or at one end only, free or fixed, so light as to permit the 

 contained larva to swim about, so heavy that it cannot leave 

 the bottom, or composed of heavy and light substances 

 blended in such proportions as to suit exactly the strength of 

 the current and the activity of the inmate. A few caddis-worms 

 make no case at all, but live free in the water, usually hiding 

 in crevices or in a sort of web of their own manufacture. 



If we examine a caddis- worm extracted from its case, an 

 operation which is easily effected by insinuating a pin or grass- 

 stalk into the hinder end, we shall find that the fore part of 

 the body is well defended by armour, while the hind part, or 

 abdomen, is soft and pale. The head bears biting mouth-parts, 

 not unlike those of a caterpillar. There are three pairs of long 

 thoracic legs, which are used in creeping, in grasping, and in 

 swimming, should the larva swim at all. Most caddis-worms 



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