3S8 



Handbook of Nature-Study 



r" 



.4 caddis-fly. 



Photo by J. T. Lloyd, 



is thrust out and we see the hind segment of the thorax which is 

 whitish, and behind this the abdomen of nine segments. At the sides 



of the abdomen, and apparently be- 

 tween the segments, are little tassels 

 of short, white thread-like gills. 

 These are filled with air, impure from 

 contact with the blood, and which ex- 

 changes its impurities speedily for the 

 oxygen from the air which is mixed 

 with the water. Water is kept flowing in at the front door of the 

 cabin, over the gills and out at the back door, by the rhythmic movement 

 of the body of the little hermit, and thus a supply of oxygen is steadily 

 maintained. 



The caddis-worm is not grown fast to its case as is the snail 

 to its shell. If we hold down with forceps a case in which the 

 occupant is wrong side up, after a few struggles to turn itself over, case 

 and all, it will turn over within the case. It keeps its hold upon the case 

 by two forward-curving hooks, one on each side of the tip of the rear 

 segment. These hooks are inserted in the tough 

 silk and hold fast. It also has on top of the first ^f^-r'r^^ 

 segment of the abdomen a tubercle, which may be 

 extended at will; this helps to brace the larva in its 



stronghold, and also permits the water to flow freely A caddis-u-'orm removed 

 around the insect. So the little hermit is en- 



from its case. 



trenched in its cell at both ends. When the log- ^^^Tlhl fal\%Tgmem "fof ' 



hoL 



iing fast to the 

 case. 



cabin species wishes to swim, it pushes almost its 



entire body out of the case, thrusts back the head, 



spreads the legs wide apart, and then doubles up, thus moving through 



the water spasmodically, in a manner that reminds us of the crayfish's 



swimming except that the caddis-worm goes head first. This log cabin 



species can turn its case over dexterously by movements of its legs. 



The front legs of the caddis-worm are so much shorter than the other 

 two pairs that they look like palpi, and their use is to hold close to the 

 jaws bits of food, which are being eaten. The other legs are used for this 

 too if the little legs cannot manage it ; perhaps also these short front legs 

 help hold the bits of building material in place while the web is woven to 

 hold it there. The caddis-worm, like the true caterpillars, has the open- 

 ing of the silk gland near the lower lip. The food of most caddis-worms 



is vegetable, usually the various 

 species of water plants ; but there are 

 some species which are carnivorous, 

 like the net-builder, which is a fisher- 

 man. 



The caddis-worm case protects its 

 inmate in two ways: First, from the 

 sight of the enemy, and second, from 

 its jaws. A fish comes along and sees 

 a nice white worm and darts after it, 

 only to find a bundle of unappetizing 

 sticks where the worm was. All of 

 the hungry predatory creatures of the 

 pond and stream would be glad to 



Pupa of caddis-fly removed froin its 



case. Xote the thread-like gills. 



Photo by J. T. Lloyd. 



