DIPTERA 



813 



The larvae of some species of the genus Sciara often attract atten- 

 tion on account of a strange habit they have of sticking together in 

 dense patches. Such assemblages of lavvse are frequently found under 

 the bark of trees. But what is more remarkable is the fact that when 

 the larvce are about to change to pupte an assemblage of this kind 

 will march over the surface of the ground, presenting the appearance 

 of a serpent-like animal. Such a congregation is commonly spoken 

 of as a Sciara-army-worm. Examples have been described that were 

 four or five inches wide and ten or twelve feet long, and in which the 

 larvae were piled up from four to six deep. The larvee crawl over 

 each other so that the column advances about an inch a minute. 



THE FAMILY SCIARID^ OF ENDERLEIN 



The establishment of a family to be known as the Sciaridee was proposed by 

 Enderlein ('i i & '12 a). The proposed family includes the subfamily Sciarinse of 

 the Mycetophilidae and the subfamily Lestremiinae of the Cecidomyiidag and is 

 characterized by the form of the eyes; the two subfamilies agreeing in having the 

 type of eyes described above (Fig. 1029) and differing in this respect from other 

 fungus-gnats and gall-gnats. 



This proposed) grouping of these two subfamilies has not been generally ac- 

 cepted. While they agree in the shape of their eyes, they differ in the presence of 

 tibial spurs in the Sciarins and the absence of these spurs in the Lestremiinae; 

 and they differ markedly in the form of their larvae. The larvae of the Lestremiinae 

 have, like those of other Cecidomyiidae, an undeveloped head, indistinct mouth- 

 parts, and a well-developed sternal spatula; the larvae of the Scarinse have, 

 on the contrary like other Mycetophilidee, a well-developed head which is strongly 

 chitinized, and strong, toothed mandibles, and do not have a sternal spatula. 



Family CECIDOMYIID^* 

 The Gall-Gnats 



The gall-gnats are minute flies which are ex- 

 tremely delicate in structure. The body and wings 

 are clothed with long hairs, which are easily rubbed 

 off. The antennse are usually long and clothed with 

 whorls of hairs (Fig. 103 1) ; but they vary greatly in 

 length, in the number of their segments, in the form 

 of the segments of the flagellum, and in the nature of 

 their clothing. Except in the first subfamily, the 

 ocelli are wanting. The legs are slender and quite 

 long, but the cox« are not greatly elongated and the 

 tibiae are without spurs. Except in the first sub- 

 family, the wing-veins are greatly reduced in nitm- m f 

 ber (Fig. 1032), the anal veins being entirely want- Fig. 103 1. — An 

 ing, and the media wanting or merely represented by tennae of gall 

 a slight, unbranched fold; in the first subfamily, the 

 Lestremiinae, vein M is well preserved. 



A striking feature of this family is the presence 

 in most species (i. e. in all except the first two small 

 subfamilies) of what have been generally known as arched filaments 



*This family is named the Itonididae by some writers, those who recognize 

 the names published by Meigen in 1800; seepage 794 for a discussion of these 

 names. 



gnats: m, male; 

 /, female, en- 

 larged more 

 than that of 

 the male. 



