A BALLOON-MAKING FLY. 



J. M. ALDRICH AND L. A. TURLEY. 



On June i6 of this year, while passing along a country road 

 near Moscow, Idaho, our attention was attracted by some bright 

 white objects moving to and fro in the air at an elevation of 

 eio-ht or ten feet. A second look seemed to indicate that these 

 objects were connected with small insects. On capturing the 

 insects they were found to be males of a species of Empis, each 

 carrying between its hind feet a peculiar structure which is 

 referred to in the title as a balloon. This is of elliptical shape, 

 about 7 mm. long (nearly twice as long as the fly), hollow, and 

 composed entirely of a single layer of minute bubbles, nearly 

 uniform in size, arranged in regular circles concentric with the 

 axis of the structure. The beautiful, glistening whiteness of 

 the object when the sun shines upon it makes it very conspic- 

 uous. The bubbles were slightly viscid, and in nearly every 

 case there was a small fly pressed into the front end of the 

 balloon, apparently as food for the Empis, as the attached 

 species were partly Chironomus and partly Oscinids, and other 

 Acalyptrate Muscids. In all cases they were dead. 



The balloon appears to be made while the insect is flying in 

 the air. Those flying highest had the smallest balloons. The 

 bubbles are probably produced by some modification of the 

 anal organs, as in Aphrophora and other leaf-hoppers, but no 

 positive observations on this point could be made. It is pos- 

 sible that the captured fly serves as a nucleus to begin the 

 balloon on. One case of a captured fly but no balloon was 

 observed. After commencing, it is probable that the rest of the 

 structure is made by revolving the completed part between the 

 hind legs and adding more bubbles somewhat spirally. The 

 posterior end of the balloon is left more or less open. 



The balloons were so light and sticky that they could not be 

 preserved with any success. The first lot obtained were placed 



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