Habitat, Food, Movements 3 



by the labrum (fig. 16), a flap hanging down in front 

 of the month, which is armed with an elaborate pro- 

 vision of hooks and spines, and is often used to drag 

 the body forwards. This use of the mouth for loco- 

 motion can be observed in other Dipterous larvae. 

 Sometimes the larva sticks out the fore end of its body 

 in search of food ; at other times the hinder end is pushed 

 out, and swayed up and down in the water ; by a similar 

 movement of the body a current of water can be made to 

 flow through the burrow ^. The larva, if undisturbed, 

 seldom or never leaves its retreat by day, but at night it 

 ventures out and swims near the surface of the w^ater, 

 writhing in figures of-eight. The body is violently 

 doubled up, and then suddenly bent to the opposite side, 

 and the blows thus given to the water propel the larva 

 slowly along. Daring these nightly excursions a store of 

 oxygen is obtained, which amply suffices for the following 

 day, when the helpless larva dares not quit its shelter. 

 Captive larvae are careless about returning to their old 

 burrows, being able to make new ones so easily, but in 

 a small vessel they will come back time after time to the 

 same burrows. If the water is well aerated and food 

 plentiful, they often remain in their tubes day and 

 night. Sometimes a number of larvae weave a felted 

 mass of earth and threads, in which each animal has 

 its own tube. 



The larvae commonly inhabit slow streams, but they 

 are also met with in pools and troughs. They can exist 

 at great depths, and have been fished up. sometimes in 

 company with Tanypus, from the bottom of Lake Geneva, 

 Lake Superior, and other deep lakes. They have often 

 been found in salt water. Packard was the first to 



' Caddis-worms and the aquatic cateiiiillar of Paraponyx, as well as 

 the Chironomus-larva, keep up an undulatory movement of the body, 

 wliich continually renews the water within the sheath, case, or burrow. 



B 2 



