THE DANCE-FLIES AND THE 

 LONG-LEGGED FLIES 



(Families Empidce and Dolichopodidce.) 



The flies of the family Empidae are rather slender, sordid, 

 uninteresting-looking creatures, usually of small size. They are 

 sometimes called dance-flies, because they are often seen in 

 swarms in the woods flying up and down with a dance-like 

 movement. By "dance-like" is not meant the slow, gliding 

 movement of modern waltz, but the robust up and down back- 

 woods jig movement. It is a very large family comprising more 

 than eleven hundred species. They resemble the robber-flies 

 somewhat in form and also in habits since they are predatory and 

 capture other insects. Some of them have the curious and as yet 

 unexplained habit of carrying little silken webs with them when 

 they fly, although no one really knows how they spin these webs 

 or where they get them. Their use has also been a mooted point, 

 but it has been suggested that they act as parachutes or aid in the 

 capture of their prey. 



Aldrich has studied what is probably this same phenomenon. 

 He finds that the males of an Empis carry little oval masses larger 

 than themselves, which are really not composed of silk, but of 

 bubbles of a viscid substance. The purpose of this structure is to 

 attract the female. Aldrich says, "When numerous males were 

 flying up and down the road it happened several times that a 

 female was seen to approach them from some chokecherry blos- 

 soms nearby. The males immediately gathered in their path and 

 she with little hesitation selected for a mate the one with the 

 largest balloon, taking a position upon his back * * * The pair 

 would settle down toward the ground, select a quiet spot * * * 

 here she would continue to hold the male beneath her for a little 

 time. The male meanwhile would be rolling the balloon about 

 in a variety of positions, juggling with it, one might almost say. 

 After the male and female parted company the male immediately 



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