97 
Dragon-flies and Damsel-flies 
brown in the female. It has a slow hovering flight and often rests on the 
tips of erect reeds with wings held perfectly horizontal. It is only on wing 
in quiet, warm sunshine; clouds or cold breezes send them quickly into 
hiding*. Among the familiar Libellulids with unblotched wings is Meso- 
therms simplicicollis, an abundant species east of the Rockies. The 
unales and young males have head, thorax, and front half of abdomen 
green, the hinder half blackish brown. In old males the body becomes 
grayish blue with a whitish bloom. Williamson says that sometimes two 
males will flutter motionless, one a few inches in front of the other, when 
suddenly the rear one will rise and pass over the other, which at the same 
time moves in a curve downwards, backwards, and then upwards, so that 
the former position of the two is just reversed. These motions kept up 
Fig. 131. —The whitetail, Plathemis lydia. (After Needham; natural size.) 
with rapidity and regularity give the observer the impression of two inter¬ 
secting circles which roll along near the surface of the water. 
The whitetail, Plathemis lydia (Fig. 131), resembles the ten-spot, but 
is one-fourth smaller. In the males also the apex of the wings is usually 
clear, not brown. The whitetail rather likes slow-flowing brooks and 
open ditches. When alight it has the habit of setting its wings aslant down¬ 
ward and forward with a succession of jerks. Needham thinks that the 
powdery whiteness of the body of the old males (in females and young males 
the body is brown marked with yellow) must render it more easily seen by 
its enemies, the king-birds and others, and thus be a disadvantage in the 
struggle for existence. He says, indeed, that the whitest ones avoid rest- 
