62 Bulletin Wisconsin Natural History Society [Vol. 11, Nos. 1-2 
WEEKS OF DANCING PRECEDE GENERAL MATING IN AT LEAST ONE 
SPECIES 
In 1910 I noted more and more clearly that out of these swarms 
mates clutch, or seize each other, whether by use of legs or clasp- 
ers, I could not distinguish. The pairs fall or drift through the 
air as if by sheer clumsiness, attached tail to tail, so drifting to 
the ground or the porch screening. Here they usually remained 
quite a while, unless rolled over and over on some smoother sur- 
face, like the cement sidewalk, by light drafts of air. The motion 
of these rolling flies is similar to the rolling parachutes or plumed 
seeds of the dandelions. Mates rarely separated in the cyanide 
bottle, dying in union although, on later drying, they fell apart easily. 
During the last two days, more and more couples were noted on 
the sidewalks in the grass and elsewhere, so that this black species 
seemed to be nearing the height of the mating season. Despite 
the fact that these swarms had been shrilly humming for the past 
two weeks, the real mating was in full swing the last two days 
only. Prof. S. J. Holmes suggests that this delay in mating may 
be due to the later emergence of the major portion of the female 
sex, since he has so proved the matter for Culicids. This may 
explain my failure to note mating couples in 1912, so late as 
June 7. 
AMATIVENESS FAILS TO MAKE MALES COMBATIVE 
A second male often attempts to attach himself to a mating 
pair, but without success, though he walks all over them in his efforts. 
I was not able to prove that two males ever actually united in 
polyandrous mating or that they mate with each other, but sev- 
eral times two males seemed to be trying to join claspers as if 
in homosexuality. Polyandry is affirmed by Mr. T. H. Taylor in 
Miall and Hammond (1900, the Harlequin Fly, C. dorsalis, p. 183). 
If one male meets another whether alone or pursuing females, the 
two males seldom attempt to drive each other away as so many 
males of larger animals will do under similar circumstances. The 
only exception is when they happen to meet head on, in walking 
on the porch screen. Then one turns aside for the other, both 
often changing their further direction. These facts gave an air 
of aimlessness to their movements. It seems to indicate that 
