1985] 
Forrest — Balloon-carrying empidid 
289 
At about sunset swarms formed beneath branches of broadleaf 
trees ( Quercus , Prunus, Myrica). Particular branches (stations) were 
used from 1 to 8 nights during a season and swarming occurred at 
some stations all four years (1981-1984). Average height of swarms 
was 1.7 m (range 0.5-4.5 m, Fig. 1). Most swarms contained fewer 
than 5 males but some swarms had over 20 males in a space of less 
than 25 X 25 X 25 cm (Fig. 2). 
Swarming started about sunset and continued for 20 minutes 
(Fig. 3A). High winds (gusts > 10 kmph) often delayed or halted 
swarming and swarms never formed at temperatures below 13°C, 
even though individuals were seen on leaves prior to the activity 
period. The starting and stopping of swarming was negatively corre- 
lated with cloud cover (r = -.8 1 , -.90, respectively; p < .05). That is, 
when greater percent of the sky was covered by clouds swarming 
started and ended earlier in the evening (Fig. 3B). 
Males in the swarms carried a 2-3 mm spherical, white, silken 
balloon below them while they flew. The balloons were hollow, did 
not contain prey, and were constructed with silk from tarsal glands 
while in flight. Male movement in swarms was easily followed by 
watching the white balloons against a background of foliage or 
males silhouetted against the sky. Males generally flew side-to-side 
in swarms and often males (balloons) collided. Twice a male was 
Swarm Height Cm) 
Figure 1. Frequency distribution of height of Hilara n. sp. swarms (n = 103, 
during spring 1982 & 83) at Green Acres Farm, Dept, of Agronomy, Gainesville, Fla. 
Two swarms at heights of 3.7 and 4.5 m are shown at 3.5 m. Arrow represents mean 
height. 
