ST. MARK'S FLY 125 



with only one pair of wings. They seem to 

 have retained the upper pair of the normal 

 insect, the lower pair being represented by 

 two small objects like drum-sticks, termed 

 halteres, or balancers. They will be clearly 

 seen on the figure of the Herb Cranefly (Plate 

 XI., Fig. 3) just behind the wings. Some- 

 times, as in the case of the Bluebottle fly 

 (Plate XI., Fig. 10), two ear-shaped lobes 

 are to be observed at the base of the wings. 

 These are called winglets. In other in- 

 stances, the flea for example, the wings have 

 been lost on account of the parasitical habits 

 of the insect, the disuse of an organ being 

 usually followed by its loss. 



I have selected a dozen flies as fairly 

 typical of the Order. St. Mark's Fly (Bibio 

 marci), Plate XI., Fig. 1, is jet black. It is 

 one of the blackest insects known. The male 

 has transparent wings, the female blackish. 

 It swarms about hedges in Spring, near the 

 festival of the Saint from whom its name is 

 derived. The Piping Gnat (Culex pipiens), 

 Plate XI., Fig. 2, is a tiny but tormenting 

 insect, yellowish-brown, and having its thorax 

 covered with short, golden-yellow hairs. It 



