AQUATIC INSECTS 



915 



the largest single complex of aquatic Diptera. They are a host; 

 indeed, the typical genus Chironomus is a host in itself. Their 

 larvae (Fig. 1384), with no better apparatus than a few blood gills 

 at the end of the abdomen, and their pupae, with nothing better 

 than "tube gills" protruded from the prothoracic spiracles, are 



FIG. 1384. The larva of Chironomus, (After Johannsen.) 



able to live in all waters, from springs to stagnant pools and from 

 rills to deep lake bottoms. They are chiefly herbivorous and are 

 of very great importance in furnishing the food of a multitude of 

 the larger animals, including fishes. The larvae construct for 



FIG. 1385. Dwelling-tubes of midge larvae (Chironomus) from the lake bottom. 

 (Photograph by T. L. Hankinson.) 



themselves some sort of shelter, fastening the materials their envi- 

 ronment offers together with the silk-like secretion of their salivary 

 glands; some in rapid streams build cases on the stones; others, 

 on the lake bottom, build soft flocculent tubes of silt (Fig. 1385). 



