A BALLOON-MAKING FLY. 
J. M. ALDRICH AND L. A. TURLEY. 
On June 16 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 
eight 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 
