m HOW TO COLLECT 



head in the male, but are more or less widely separated in the 

 female. With the exception, however, of a few small families, 

 this does not apply to the Oithorrhapha Nematocera [Gall-midges 

 {Cecidomyidm), Fungus-midges (Mycetophilidce), Chironomidce, 

 Culicidre, and Ti'pulidxv], the Diptera that are gnatlike in shape 

 and possess long antennae ; neither is the character found in the 

 Robber-Hies (Asilidce), the Dolichopodidce (shining green, narrow- 

 bodied, long-legged flies, usually found in the vicinity of water), nor 

 in the vast army of Diptera (chiefly of small or moderate size) 

 included in the families which it is customary to designate compre- 

 hensively by the term Acahjpterate Muscidce. In these cases, where 

 no sexual distinction is furnished by the eyes, it is usually possible 

 to determine the sex by an examination of the terminal segments 

 of the abdomen : in the male the abdomen ends more bluntly, while 

 the clasping organs are often very conspicuous ; in the female the 

 tip of the abdomen is generally more or less tapering, showing 

 indications of the presence of an ovipositor, which is often extruded. 

 In the Mosquitoes {Culicidm *) the sexes can be readily distinguished 

 by the antennre, which in the male are plumose, forming tufts in 

 front of the head, while in the female they are nearly bare ; in the 

 Midges also (Chironoinidce) tlie antennae in the male form plumes, 

 while in the female they are quite short and inconspicuous. In 

 certain families (DoUchopodid<6, Empidce) secondary sexual characters 

 are often furnished by the legs; where this is the case, it usually 

 takes the shape of abnormal expansions of some of the tarsal joints 

 in the male. 



As a rule among Diptera the sexes of the same species are alike in 

 coloration^ or at any rate resemble one another pretty closely, 

 striking s?xual differences in this respect (such as are commonly 

 seen among butterflies) being exceedingly rare. 



When and Where to look for Diptera. 



With the exception of Mosquitoes, Midges, and similar forms, 

 Diptera are most active when the sun is shining. In hot countries 



* For collecting this family, see special iustructions ('-flow to Collect 

 Mosquitoes"), pp. Hl-Ol, 



