1969] 
Willey and Willey — Social Displays 
283 
rated from the next sequence by a fractional-second pause. This 
spurt-walk becomes accentuated by a rapid raising and lowering 
of both hind legs with an open femoro-tibial angle of about 30°. 
One or two such flicks may occur whenever both hind legs are not 
in contact with the ground. The male, when approaching a high 
point, such as a pebble or a stick, often crawls! upon it and stands 
in a motionless “alert pose” as in Figure 1. At this time the male 
is very responsive to any sudden movement: or sound on the part of 
the observer. Usually the visible reaction to a disturbance is a slight 
crouch , lifting of the antennae to the vertical, closing of the femoro- 
tibial angle of the hind legs and lowering of the hind femora to 
the horizontal. The subsequent reaction is usually a leap and flight. 
If the male is allowed to recover from the initial disturbance, he 
slowly resumes the alert pose and periodically snaps the hind femora 
to the vertical in a flicking motion up and down, singly or together. 
Minor disturbances such as small insects coming too close or a grass 
blade touching him will cause such a flick. In fact, some flicks seem 
to be spontaneous during the alert pose. 
Social behavior 
Signals associated with social interaction are ( 1 ) spontaneous 
flights which are accompanied by a clicking sound (crepitation) pro- 
duced by the wings, (2) simple soundless flicks of the hind legs 
(“femur-tipping”, Otte, 1968), (3) femoro-tegmina .1 stridulations 
which generate chirps, rasps, buzzes and squeals; and (4) soundless 
movements observed during contact between two grasshoppers which 
include tapping with the prothoracic tarsus, palpating with the 
antennae, rapid stroking with the palpi, butting with the frons, 
mounting by the male and, of course, genital contact. The emphasis 
in this paper will be placed on those signals transmitted at a distance 
between two or more individuals. 
A signal, by our definition, must have some reaction-potential in 
the organism perceiving it. Our operational definition for a visual 
or auditory communication signal is the production of a measurable 
motion and/or airborne acoustical vibration by one individual fol- 
lowed in another individual by an action unrelated to what the 
latter was doing and unlikely to have occurred in the absence of the 
stimulation. Chemical signals could not be recorded in the present 
study. Frequent sounds such as mandible clicks, wing buzzes, sub- 
strate tapping with the tarsi, and tibio-tegminal clicks have produced 
no observable response in this species, and will not be considered 
in detail. 
