CHEMORECEPTION AND THE BEHAVIOR OF INSECTS
159
tract with the far side of the trail to be able to pick it up again. On the
other hand, if the trail was broken by drawing the finger across it as
Bonnet did, the ant was repelled by the strange scent and turned away
without attempting to cross the gap. The ant's ability to maintain a
heading in the absence of a repellent scent is the mechanism whereby
it is able to extend its trails gradually into new and unexplored territory.
Carthy's (1950) results confirm the conclusions of Bethe and Brun by
demonstrating the importance of the odor trail in this speciees.
Santschi (1911, 1923), studying the ant Tapinoma, noticed that foragers returning from food flexed the abdomen so that the gaster rubbed
against the substrate. Close examination revealed that tiny droplets
were deposited by this action. He supposed these to be the products
of the anal gland and the means whereby a trail was laid and nest-mates
informed of the finding of food. The consensus is now that any general
excitement causes this excretion, that it is not "deliberate." Although
the pulvinate glands are situated ventrad to the anus and would logically
be the source of the material deposited, experiments by Carthy (1950)
suggest very strongly that excretion from the anus rather than secretion
from the glands produces the material concerned. Although ants fed
with various dyes laid variously colored trails, this action is not conclusive evidence that anal products are responsible because, as Carthy
pointed out, the dye could easily get into the hemocoele and eventually
into the glands. Carthy's most convincing evidence is derived from an
experiment in which workers of A. fuliginosus were fed mixtures of
sugar and charcoal. In the tracks so produced there were clearly small
particles of charcoal. There is no indication, however, that the anal
glands were not also contributing substance to the trail. Attempts to
analyze the chemical trail have not been particularly informative, since
the microscopic amounts of substance preclude extensive chemical work.
However, the substance has a pH of ca. 6.8, is very soluble in water,
insoluble in alcohol and chloroform, lacking in fat, strongly positive for
protein, and possibly contains uric acid and reducing sugars. Formic
acid appears to be absent, and ants fail to follow an artificial trail made
with formic acid although they do tend to follow such a trail made with
an aqueous extract of one of the workers. These tests certainly disprove
Bethe's contention that the trail consists of footprints.
Bethe also believed that the trails were polarized, that the ant could
perceive from the trail that direction in which the nest lay and that in
which the food was to be found. Brun, in his studies of A. fuliginosus,
came to the conclusion that honey-trails, that is, trails over which food
was being carried, were polarized in the sense of being olfactorily
different at different points but that larva-trails, those over which larvae
159
tract with the far side of the trail to be able to pick it up again. On the
other hand, if the trail was broken by drawing the finger across it as
Bonnet did, the ant was repelled by the strange scent and turned away
without attempting to cross the gap. The ant's ability to maintain a
heading in the absence of a repellent scent is the mechanism whereby
it is able to extend its trails gradually into new and unexplored territory.
Carthy's (1950) results confirm the conclusions of Bethe and Brun by
demonstrating the importance of the odor trail in this speciees.
Santschi (1911, 1923), studying the ant Tapinoma, noticed that foragers returning from food flexed the abdomen so that the gaster rubbed
against the substrate. Close examination revealed that tiny droplets
were deposited by this action. He supposed these to be the products
of the anal gland and the means whereby a trail was laid and nest-mates
informed of the finding of food. The consensus is now that any general
excitement causes this excretion, that it is not "deliberate." Although
the pulvinate glands are situated ventrad to the anus and would logically
be the source of the material deposited, experiments by Carthy (1950)
suggest very strongly that excretion from the anus rather than secretion
from the glands produces the material concerned. Although ants fed
with various dyes laid variously colored trails, this action is not conclusive evidence that anal products are responsible because, as Carthy
pointed out, the dye could easily get into the hemocoele and eventually
into the glands. Carthy's most convincing evidence is derived from an
experiment in which workers of A. fuliginosus were fed mixtures of
sugar and charcoal. In the tracks so produced there were clearly small
particles of charcoal. There is no indication, however, that the anal
glands were not also contributing substance to the trail. Attempts to
analyze the chemical trail have not been particularly informative, since
the microscopic amounts of substance preclude extensive chemical work.
However, the substance has a pH of ca. 6.8, is very soluble in water,
insoluble in alcohol and chloroform, lacking in fat, strongly positive for
protein, and possibly contains uric acid and reducing sugars. Formic
acid appears to be absent, and ants fail to follow an artificial trail made
with formic acid although they do tend to follow such a trail made with
an aqueous extract of one of the workers. These tests certainly disprove
Bethe's contention that the trail consists of footprints.
Bethe also believed that the trails were polarized, that the ant could
perceive from the trail that direction in which the nest lay and that in
which the food was to be found. Brun, in his studies of A. fuliginosus,
came to the conclusion that honey-trails, that is, trails over which food
was being carried, were polarized in the sense of being olfactorily
different at different points but that larva-trails, those over which larvae