90 
Psyche 
[March 
arrow head ( Sagittaria latifolia). Observations were made daily 
until August 8, by which time the water had dropped to such a level 
that few emergent perches suitable for Pachydiplax longipennis re- 
mained. On August 12, observations were commenced at a third 
shallow, artificial pond off Shade Street in Lexington. This 1.2 
hectare pond was completely surrounded by trees ( Acer rubrum 
and Alnus sp.) and emergent sticks and logs suitable for perches 
were plentiful. 
At the Five Fields pond, attempts were made to study behavior 
by marking males. These attempts were largely unsuccessful due 
primarily to failure to relocate marked individuals. Thereafter, 
identifications of individuals were made by recording natural vari- 
ations. 
Some preliminary studies were made of the ultraviolet reflectant 
properties of the blue-grey abdominal pruinescence. With the col- 
laboration of Robert E. Silberglied (Department of Biology, Har- 
vard University) ultraviolet patterns were examined, using a 35 mm 
single-lens- reflex camera with Zeiss F.4, 60mm Ultraviolet Objektiv 
lens, Zeiss UV 366 filter (=Wratten 18A), Bowens Texturelight 
electronic flash, Kodak Tri-X Pan film, and Acufine developer. 
Although most of my observations confirm those of Johnson 
(1962), I found that there was a difference in male perching be- 
havior. These and some additional observations are reported below. 
Male-Male Interactions 
From the time of their arrival (approx. 10 a.m.) until their de- 
parture (approx. 4 p.m.), the males observed defended a defined 
territory as described by Johnson (1962). The “threat display” 
(Johnson, 1962) was also frequently seen. Following this display, 
I observed that the two males engage in further agonistic behavior. 
One male pursues the other in a horizontal direction with abdomen 
raised while the leading insect flies with abdomen lowered (Fig. ia). 
The two may repeat this behavior several times, exchanging positions 
and/or reversing direction after flying a distance of 1-2 meters. 
(They may alternatively resume the “threat display.” Occasionally 
this may involve only one male if the other has returned to a perch.) 
After a variable duration (usually less than a minute) this pursuit 
behavior is discontinued and the males may begin a third behavior, 
as Johnson (1962) noted. Then, as I observed, the male who does 
succeed in getting the lower position, flies upwards, forcing the other 
up with him as much as 15 meters into the air at an angle of 50-80 
