158 Illinois State Laboratory of Natural Historij. 



Family Chironomid.^. (Gnats.) 



The familiar aquatic larvne of this family belong to the 

 genus Chiron omus. Probably no other one genus of insects 

 constitutes as important an item in the food of as large a num- 

 ber of fishes. They may be recognized by their uniformly 

 cylindrical bodies, small heads, enclosed in an opaque crust, and 

 with a bilobed foot-like process bearing a dense brush of curved 

 bristly hairs extending forward beneath it. At the posterior 

 end of the body is a pair of false feet, also characteristic, each 

 bearing a circlet of retractile hooks. The head is smaller rela- 

 tively than that of the larva of Corethra, but under the micro- 

 scope the parts appear almost as complicated. The structures 

 present, however, are mainly in the nature of biting organs, 

 the parts having to do with perception being here poorly de- 

 veloped. Thus the jaws are well developed, the edges of the 

 mouth-opening are furnished with numerous teeth and hooks, 

 and the labium is a broad plate with strongly toothed edge, 

 while, on the other hand, the eyes and antennae are very small. 

 All this corresponds with what is known of the food of the 

 larvae. Their digestive tube is often filled with a brown granu- 

 lar material, consisting, as nearly as can be made out with the 

 microscope, of decomposed organic matter containing great 

 numbers of bacteria and a good many empty frustules of 

 diatoms. In one example was found the fragments of an in- 

 sect. The organs for mastication, complicated as they are, 

 would hardly be equal to the complete obliteration of the cell- 

 structure of plants and animals, were these the aliment upon 

 which the larvae depended, and I believe that the material in 

 the alimentary canals examined was dead when taken. The 

 diatoms were not more frequent than they would be if taken in 

 the slimy coating which collects on submerged objects. The 

 insect fragments, which were of rather large size, bore evidence 

 of having formed a rejected skin; while the abundance of bac- 

 teria among the alimentary contents points also in the same 

 direction. 



The larva! are often of a blood-red color. They swim by 

 a wriggling movement when in open water, but commonly live 

 at the bottom, under stones and rubbish, where they construct 



