CHEMORECEPTION AND THE BEHAVIOR OF INSECTS
163
dried up with the consequent loss of its volatility. Carthy pointed out
that a successful forager returns to the nest on a fresh trail which must
be followed back by new foragers without a guide. In order to select the
correct trail among the maze of exploratory trails it is expedient for
foragers to follow the freshest trail. Therefore, as long as many foragers
use a trail it is successful and retains its power by constant refreshening, whereas a trail no longer in use gradually effaces itself. Unsuccessful foragers, apparently not being excited, lay no detectable trail. The
laying of a usable trail depends then upon the amount of excitation and
the amount of use in order to allow economy in the use of foraging
parties (Carthy, 1950). In the case of army ants the requirements for
fresh trails do not exist; hence a persistent trail is of value. In the case of
army ants the ant will follow the trail of any colony, although its
hesitant behavior suggests that it can distinguish this from its own. If
it meets with the rightful owners of the trail, it is killed unless it steps
aside. MacGregor showed that different Myrmica colonies also had
distinct odor trails which could be distinguished by the ants. He suggested that trail odor and colony odor are the same.
It is clear from the work on the three species mentioned that trailfollowing depends on more than one sense perception, although one may
predominate. The degree to which any one sense does predominate
varies with the species. Thus, some ants are predominantly visual species,
whereas others depend more on the chemical senses. There are counterparts among the dogs, some of which rely greatly on vision, while others
depend upon olfaction. There is evidence, furthermore, that the ant does
indeed possess a vocabulary of senses, as Schneirla (1929, 1953) maintained, from which it can select the most appropriate as the changing
situation demands. Some of the maze studies carried out by Schneirla
(1953) tend to illustrate this point. After an ant has learned to run a
maze with the light coming from one direction, the direction of the light
is altered and the ant is given an opportunity to relearn the maze. If
during this period of relearning a piece of the floor of the true way is
exchanged with a piece from a blind alley, the ant is more disturbed
than she would be were the change made without the illumination also
having been changed. From these and similar experiments it seems that
the ant places greater reliance upon tactile and olfactory cues during
periods of adjustment to the light stimulus than at other times.
It is the consensus that ants depending on visual stimuli, especially
individual foragers which do not follow a collective route, must learn
the route. The case for followers of chemical trails is less clear-cut.
Forel was of the opinion that the chemical trail was neutral from the
point of view of behavior and that trail-following had to be learned.
163
dried up with the consequent loss of its volatility. Carthy pointed out
that a successful forager returns to the nest on a fresh trail which must
be followed back by new foragers without a guide. In order to select the
correct trail among the maze of exploratory trails it is expedient for
foragers to follow the freshest trail. Therefore, as long as many foragers
use a trail it is successful and retains its power by constant refreshening, whereas a trail no longer in use gradually effaces itself. Unsuccessful foragers, apparently not being excited, lay no detectable trail. The
laying of a usable trail depends then upon the amount of excitation and
the amount of use in order to allow economy in the use of foraging
parties (Carthy, 1950). In the case of army ants the requirements for
fresh trails do not exist; hence a persistent trail is of value. In the case of
army ants the ant will follow the trail of any colony, although its
hesitant behavior suggests that it can distinguish this from its own. If
it meets with the rightful owners of the trail, it is killed unless it steps
aside. MacGregor showed that different Myrmica colonies also had
distinct odor trails which could be distinguished by the ants. He suggested that trail odor and colony odor are the same.
It is clear from the work on the three species mentioned that trailfollowing depends on more than one sense perception, although one may
predominate. The degree to which any one sense does predominate
varies with the species. Thus, some ants are predominantly visual species,
whereas others depend more on the chemical senses. There are counterparts among the dogs, some of which rely greatly on vision, while others
depend upon olfaction. There is evidence, furthermore, that the ant does
indeed possess a vocabulary of senses, as Schneirla (1929, 1953) maintained, from which it can select the most appropriate as the changing
situation demands. Some of the maze studies carried out by Schneirla
(1953) tend to illustrate this point. After an ant has learned to run a
maze with the light coming from one direction, the direction of the light
is altered and the ant is given an opportunity to relearn the maze. If
during this period of relearning a piece of the floor of the true way is
exchanged with a piece from a blind alley, the ant is more disturbed
than she would be were the change made without the illumination also
having been changed. From these and similar experiments it seems that
the ant places greater reliance upon tactile and olfactory cues during
periods of adjustment to the light stimulus than at other times.
It is the consensus that ants depending on visual stimuli, especially
individual foragers which do not follow a collective route, must learn
the route. The case for followers of chemical trails is less clear-cut.
Forel was of the opinion that the chemical trail was neutral from the
point of view of behavior and that trail-following had to be learned.