158
V. G. DETHIER
hole to the nest. This hole could be blocked and its position altered by
rotation. Although the ant oriented to the edge of the arena by visual
cues, it located the exit hole by palpating with its antennae, thus presumably by scent. That scent may be of some importance is also shown
by altering the olfactory background. Cleaning the substrate causes
some disturbance in orientation, and crushing a companion near the
trap door causes a worker to halt and retreat. This effect is reminiscent
of the manner in which "Schreckstoffe" emanating from wounded fish
acts as a repellent and a warning to other fish. The existence of odor
streaks adjacent to the pile of larvae which the workers are removing
can be demonstrated by dusting with lycopodium powder. However,
these streaks never join to form a trail and indeed may sometimes not
occur at all. When workers are excited, as when finding larvae or when
losing their way, they tend to deposit streaks. It is possible that the odor
streaks of this species may be of considerably more importance when
numbers of workers are foraging than when an individual is working
alone. As Carthy pointed out, the suspicion that there is a difference
between the mode of orientation by an individual and that characteristic
of a group may well explain the inability of Bethe to confirm Lubbock's
experiments and his final conclusion regarding the importance of odor
in orientation by this species. In nature the trails of this ant (A. niger)
may be disrupted by drawing a finger across the substrate, but the result
may be accounted for by the possibility of a repellent odor emanating
from the finger. In any event, here is an ant which orients primarily
by visual cues and pays attention to the general olfactory background
without, however, utilizing the latter as a prime means of trailing. The
workers run in long smooth curves with the antennae held erect at a
small angle above the substrate. If blinded, the forager adopts a slower
gait and palpates the ground with its antennae. Thus handicapped, it
behaves very much like the related species A. fuliginosas, which progresses in short rushes with its antennae touching the ground in order
to pick up the chemical trail upon which it is chiefly dependent.
In marked contrast to species like A. niger, A. fuliginosus is quite
independent of visual stimuli in trail-finding. It runs a comparatively
slow erratic zig-zag trail, the direction of which is not influenced by any
alteration of light or other visual cues. On the other hand, it is completely disoriented when the trail is cleaned with water followed by
alcohol, and drying. Its trail could be seen by dusting with lycopodium
powder (Carthy, 1950). When this trail was disrupted by wiping away
with clean cotton wool a portion one inch long, there was no disturbance,
because the ant on approaching this gap persisted in its direction for
about three-fourths of an inch and thus came into sufficiently close con-
V. G. DETHIER
hole to the nest. This hole could be blocked and its position altered by
rotation. Although the ant oriented to the edge of the arena by visual
cues, it located the exit hole by palpating with its antennae, thus presumably by scent. That scent may be of some importance is also shown
by altering the olfactory background. Cleaning the substrate causes
some disturbance in orientation, and crushing a companion near the
trap door causes a worker to halt and retreat. This effect is reminiscent
of the manner in which "Schreckstoffe" emanating from wounded fish
acts as a repellent and a warning to other fish. The existence of odor
streaks adjacent to the pile of larvae which the workers are removing
can be demonstrated by dusting with lycopodium powder. However,
these streaks never join to form a trail and indeed may sometimes not
occur at all. When workers are excited, as when finding larvae or when
losing their way, they tend to deposit streaks. It is possible that the odor
streaks of this species may be of considerably more importance when
numbers of workers are foraging than when an individual is working
alone. As Carthy pointed out, the suspicion that there is a difference
between the mode of orientation by an individual and that characteristic
of a group may well explain the inability of Bethe to confirm Lubbock's
experiments and his final conclusion regarding the importance of odor
in orientation by this species. In nature the trails of this ant (A. niger)
may be disrupted by drawing a finger across the substrate, but the result
may be accounted for by the possibility of a repellent odor emanating
from the finger. In any event, here is an ant which orients primarily
by visual cues and pays attention to the general olfactory background
without, however, utilizing the latter as a prime means of trailing. The
workers run in long smooth curves with the antennae held erect at a
small angle above the substrate. If blinded, the forager adopts a slower
gait and palpates the ground with its antennae. Thus handicapped, it
behaves very much like the related species A. fuliginosas, which progresses in short rushes with its antennae touching the ground in order
to pick up the chemical trail upon which it is chiefly dependent.
In marked contrast to species like A. niger, A. fuliginosus is quite
independent of visual stimuli in trail-finding. It runs a comparatively
slow erratic zig-zag trail, the direction of which is not influenced by any
alteration of light or other visual cues. On the other hand, it is completely disoriented when the trail is cleaned with water followed by
alcohol, and drying. Its trail could be seen by dusting with lycopodium
powder (Carthy, 1950). When this trail was disrupted by wiping away
with clean cotton wool a portion one inch long, there was no disturbance,
because the ant on approaching this gap persisted in its direction for
about three-fourths of an inch and thus came into sufficiently close con-