NEMATOCERA : HARMLESS NEMATOCERA 131 



coincided with an epidemic of that disease. In the subfamily {Sciarina) 

 to which Sciara belongs the coxae are only moderately elongated and 

 the form of the body is often not characteristically gnat-like. 



Family BiBIONlD/E (Lat. Bibio = a. must insect). 



The species of this family are found in most parts of the world ; some 

 of them, in northern latitudes, appear in swarms in the spring. In colour 

 they are generally black or red, or sometimes yellow ; and in form they 

 are often stout and unmidgelike. The antennae, which are shorter than 

 the thorax and do not bear whorls of hairs, are composed of numerous 

 (8 to i5) short, broad, compact segments. The tibiae of the front legs 

 end in a hook or a circlet of small spines. The wings are large and the 

 costa does not extend beyond their tip. Ocelli are present and are very 

 distinct, and in the male the compound eyes are generally large and are 

 sometimes hairy. The larva has a well-formed head with biting mouth- 

 parts ; there are belts of bristles or spines round the trunk-segments, 

 and numerous lateral spiracles. The larvae of some species feed on the 

 roots of plants and may do injury to grass and crops. A British species 

 of this family, Dilophus febrilis, is known as the fever-fly. 



Family BLEPHAROCERlDiE (Gr. j3X60apt's = eyelash ; /c^/)as = antenna). 



This is a small group of mosquito-like flies found mostly in America 

 in the neighbourhood of streams, but also occurring in Europe and Asia, 

 They are distinguished from all other flies by the wings, which in addition 

 to the ordinary venation have a fine net-work of creases (" secondary 

 venation ") resulting from the folding of the wings in the pupal stage. 

 According to Williston the proboscis is elongate, as are the other mouth- 

 parts, and in the female long slender serrated mandibles are present, 

 the female being predaceous on other flies. The antennae are slender 

 and are without whorls of hairs. On the scutum, in front of the wings, 

 there is an interrupted transverse suture. The larvae, which live in rapid 

 streams, are said to resemble a small Crustacean rather than the larva of 

 an insect ; they are composed of a small number of segments separated 

 by deep constrictions, and on the ventral surface there is a row of suckers 

 some of which bear tufts of tracheal gills. The pupae also are said to be 

 peculiar, having a soft flat ventral surface with suckers for clinging to 

 stones in the bed of the streams in which they live, and a hard convex 

 dorsal surface from which, anteriorly, a pair of tracheal breathing-organs 

 projects. 



Family Orphnephilid^ (Gr. 8/)0i'i) = gloom ; <j)CKelv=io love). 



This family includes a single genus Orfihnephila, the species of which, 

 though few in number, are widely distributed. They are small brown or 

 yellowish flies with antennae that appear to consist of 2 segments and a 

 terminal arista ; but both the 2nd segment and the arista are complex 

 and are together composed of 10 or 11 subsegments. In both sexes 

 the eyes are large and meet across the head. 



