CHEMORECEPTION AND THE BEHAVIOR OF INSECTS
157
merous obstacles and subject to constant change. Early investigators
erred in assuming that a single sense exercised absolute control over
orientation, that the problems of trail-finding are the same under all
conditions, that a given species exhibits only one kind of trail orientation, and that closely related species behave similarly. In matter of
fact there are many different forms of trail orientation utilized by insects.
There are, for example, individual trails and mass or collective trails, exploratory trails and established trails, foraging trails and homing trails,
those extending over short distances and those extending over wider
areas.
In general, the two senses most used in trailing of all sorts are vision
and the chemical senses. Vision dominates the trail orientation of individual foragers, which depend a great deal on light, its plane of polarization, and the spatial arrangements of objects. The route is learned.
Collective foragers depend heavily upon chemical trails. They may follow
these trails in a rigid stereotyped manner as do the army ants, Eciton,
or they may, like the ant A. fuliginosas, gradually perfect and economize
from a tangled skein of trails the one which is to bear the brunt of the
traffic. It must be stressed, however, that, although one sense may be
dominant in trailing, it is not used to the exclusion of the others; and
the relative importance of one sense over another may vary from condition to condition. For example, Lubbock (1884), studying trail orientation in individuals of Acanthomyops
(Lasius)
niger, an ant which
forages in loose columns, found that although light was of extreme
importance in orientation the ants
. . do not derive by any means so
much assistance from their eyes as we should under corresponding
circumstances." Moreover, odor is not completely unimportant. Bethe
(1898), repeating the experiments, but with numbers of foragers, could
not demonstrate dependence upon light and concluded that the ant
relied upon an odor trail. Brun (1914) subsequently showed that a light
compass reaction was indeed important in orienting the ant. In an
attempt to resolve these conflicts Carthy (1951) restudied the species in
detail. He was able to demonstrate that light was certainly important.
As Lubbock had before him, Carthy studied a homing trail and employed a pile of larvae as the stimulus to induce the ants to return home.
Larvae provided a better stimulus than food, because with feeding the
food drive gradually diminishes, while the drive to return larvae remains
at a high level until all larvae are returned. Carthy's results showed that
vision was of prime importance, and that this may be assisted by an
ability to orient to the polarization plane of light. The work also
showed, however, that scent is of some importance. In the experiment,
a pile of larvae was placed in the center of an area which had an exit
157
merous obstacles and subject to constant change. Early investigators
erred in assuming that a single sense exercised absolute control over
orientation, that the problems of trail-finding are the same under all
conditions, that a given species exhibits only one kind of trail orientation, and that closely related species behave similarly. In matter of
fact there are many different forms of trail orientation utilized by insects.
There are, for example, individual trails and mass or collective trails, exploratory trails and established trails, foraging trails and homing trails,
those extending over short distances and those extending over wider
areas.
In general, the two senses most used in trailing of all sorts are vision
and the chemical senses. Vision dominates the trail orientation of individual foragers, which depend a great deal on light, its plane of polarization, and the spatial arrangements of objects. The route is learned.
Collective foragers depend heavily upon chemical trails. They may follow
these trails in a rigid stereotyped manner as do the army ants, Eciton,
or they may, like the ant A. fuliginosas, gradually perfect and economize
from a tangled skein of trails the one which is to bear the brunt of the
traffic. It must be stressed, however, that, although one sense may be
dominant in trailing, it is not used to the exclusion of the others; and
the relative importance of one sense over another may vary from condition to condition. For example, Lubbock (1884), studying trail orientation in individuals of Acanthomyops
(Lasius)
niger, an ant which
forages in loose columns, found that although light was of extreme
importance in orientation the ants
. . do not derive by any means so
much assistance from their eyes as we should under corresponding
circumstances." Moreover, odor is not completely unimportant. Bethe
(1898), repeating the experiments, but with numbers of foragers, could
not demonstrate dependence upon light and concluded that the ant
relied upon an odor trail. Brun (1914) subsequently showed that a light
compass reaction was indeed important in orienting the ant. In an
attempt to resolve these conflicts Carthy (1951) restudied the species in
detail. He was able to demonstrate that light was certainly important.
As Lubbock had before him, Carthy studied a homing trail and employed a pile of larvae as the stimulus to induce the ants to return home.
Larvae provided a better stimulus than food, because with feeding the
food drive gradually diminishes, while the drive to return larvae remains
at a high level until all larvae are returned. Carthy's results showed that
vision was of prime importance, and that this may be assisted by an
ability to orient to the polarization plane of light. The work also
showed, however, that scent is of some importance. In the experiment,
a pile of larvae was placed in the center of an area which had an exit