vir EMPIDAE- -DOLICHOPIDAE 493 



large hind legs. Ill Hemerodroirnia the front legs are raptorial, 

 the femora being armed with spines on which the tibia^ 

 close so as to form a sort of trap. Many Empidae execute 

 aerial dances, and some of the species of the genus Jfil/im are 

 notorious for carrying veils or nets in the form of silken we] is 

 more or less densely woven. This subject is comparatively new, 

 the fact having been discovered by Baron Osten Sacken in 

 18T7, 1 and it is not at all clear what purpose these peculiar 

 constructions serve ; it appears probable that they are carried 

 by means of the hind legs, and only by the males. Mik thinks 

 that in H. sartor the veil acts as a sort of parachute, and is of 

 use in carrying on the aerial performance, or enhancing its 

 effect ; while in the case of other species, H. inn urn and H. infrr- 

 stincta, the object appears to be the capture or retention of prey, 

 after the manner of spiders. The source of the silk is not 

 known, and in fact all the details are insufficiently ascertained. 

 The larvae of Empidae are described as cylindrical maggots, with 

 very small head, and imperfect ventral feet ; the stigmata are 

 ainphipneustic, the thoracic pair being, however, excessively 

 small ; beneath the posterior pair there is nearly always a tooth- 

 or spine-like prominence present. 



Fam. 27. Dolichopidae.- Graceful flies of metallic colour*. 

 of moderate or small size, and long legs ; usually with bristles on tin' 

 tliuraj: <nnl A //.-., the halteres exposed, squamae 

 b< ing tjiiif,' iibxnit ; <mfe H /tae of tt>-<> x/mrt stout 

 joints (of '/rli'n-h the second is really two, its 

 dirision It'in// more or less d/*//n<-fy, with a 

 thread-like or Imir-liL-e appendage. Proboscis 

 short, j/i'xhi/. Cltnr*, puIriHi, and empodium 

 small ; wings witji a simple .s//.s-/V/// <>f nervures, 

 finite on the 'posterior part of tin 1 //in// are but 

 few, there is no anterior Im^/l cross-vein be- 

 tween the dise/d and second basal cells, whirh 



therefore form b./t one cell. This is also a FIG. 235.-A i ,n., 



B. pupa of Juede- 

 very extensive family of Hies, of which we 



have probably about "2 00 species in Britain. p"^ 6 ' 



They are conspicuous on account of their 



golden, or golden-green colours, only a few being yellow or black. 



1 Ent. May. xiv. 1877, p. 226 ; for a discussion of the subject see Mik, Wien. 

 fnt. Zeit. xiii. 1894. p. 273. 



