THE MOTH- FLIES 



(Family Psychodidce.) 



There are certain very small, weak flies which look like little 

 moths, from which fact they have been termed "moth-flies," 

 which are frequently found upon windows and upon the under 

 surfaces of leaves, and which have broad wings, rather thick 

 antennae, and which are densely clothed with hairs, even the 

 surface of the wings being hairy. These are the flies of the 

 family Psychodidae. They are so small and so fragile that they 

 are difficult to preserve, and though there are probably very many 

 species only comparatively few have been described. 



The arrangement of the wing veins in these flies differs from 

 that of all other flies, and possibly represents the lowest or most 

 generalized type in the Diptera, although there is good reason to 

 believe that perhaps the Tipulidae more nearly represent the pri- 

 mordial fly. 



In larval habits they are interesting and variable. Some of 

 them live in dry cow dung; others on fallen leaves immersed in 

 the water of pools or small streams, while others live in rapidly 

 running water, and others are found in rotten potatoes. The 

 larvae are remarkable from the fact that they have both tracheal 

 gills and open spiracles, so that they can theoretically both breathe 

 air and use the oxygen in the water. 



One of the European forms (Pericoma canescens) has been 

 carefully studied by Miall and Walker (Trans. Ent. Soc. London, 

 1895), but the larvae of none of the American forms were known 

 until very recently, when Kellogg discovered the larvae of Peri- 

 coma calif or niensis in the streams of the Sierra Morena Mountains 

 near Stanford University, California. With Kellogg's larva no 

 tracheal gills were found but they may have been retracted. On 

 the under side of the larva are curious sucking discs, through 

 which it attaches itself to objects under the water, a structure 

 which seems to be necessary in order to prevent the larva from 



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