210 
Psyche 
[September 
Mormolyce, and others which live normally beneath bark. 
The movement of testaceus is peculiar. The individuals 
observed are given to frequent, short pauses in their run- 
ning, and exhibited an unusually quick change of pace and 
direction. In consequence of this behavior, their normal gait 
is a darting movement. 
The speed of these three species, and of the host, Formica 
ulkei, may be mentioned as interesting. Individuals were 
Fig. 1. Tachyura incurva (Say) feeding on the host ant, Formica ulkei 
Emery. Photographed from life by Carl Welty. 
placed on a wide expanse of concrete floor, their path traced 
in with chalk and the distance covered in a unit of time 
taken with a stop watch. 
Workers of Formica ulkei , and the predator, Tachyura 
incurva are both relatively rapid travelers, moving, when 
stimulated, between 150 and 200 centimeters per minute. 
Ulkei workers, however, do not hold this speed for repeated 
trials. 
