116 
Psyche 
[Vol. 95 
cases a screen was laid over the pile of vegetation to make it easier to 
spot pairs before they became hidden in the vegetation. Video 
recordings of four copulating pairs were analyzed frame by frame 
(30 frames/ sec.); two other pairs were observed with lenses giving 
4-8X magnification. 
Flies were raised from a pile of cut vegetation which had been left 
on the ground for 3 days, then placed in a gunny sack with a clear 
plastic bag attached to its open end. Voucher specimens are de- 
posited in the U.S. National Museum, Washington, DC 20560. 
Results 
Male flies began to arrive within 5-10 minutes after the vegetation 
was cut, and often accumulated in large numbers (up to more than 
30 per square meter) within 30 minutes. They alternately perched on 
the vegetation, and flew, often in short darting flights toward other 
flies, producing brief collisions and clashes, or short pursuits. They 
did not defend territories, but gradually drifted over the cut vegeta- 
tion and nearby plants. Occasionally they hit and momentarily 
seized other males that were either perched or, more rarely, in flight. 
On four occasions a male bumped briefly against a mating pair 
resting on the vegetation, but none of the pairs separated as a result. 
Flies collected in two aggregations about one hour after vegetation 
was cut were nearly all males (31 of 32 and 41 of 41). 
I saw the initial stages of pair formation on two occasions. The 
male seized the female in the air 1-2 cm over the vegetation and the 
pair immeditely landed, with the male on the female’s dorsum. The 
male immediately made genital contact as he scrambled briefly with 
his front legs on the female’s head. Then he rested quietly on her 
dorsum for <5 seconds before beginning a series of courtship 
movements. Although the durations and sequences of the move- 
ments varied somewhat, at least three types of behavior were 
recognizable. 
Tapping 
A male tapped by raising his front legs, usually holding them 
briefly immobile as they projected more or less forward over the 
female’s head, then “winding up” by bringing them sharply back and 
upward over his head, and then “swinging” them sharply downward 
over the female’s head with a whipping motion (Figs. 1 and 2). The 
leg usually (perhaps always) stopped just short of hitting the 
