Excerpt from the paper by Sam S. Fluker, "Sympatric associations among selected ant species and some effects of ants on sugarcane mealybugs in Hawaii" (1969)
In tests conducted in the laboratory, it was found that when colonies of Argentine ants (
Linepithema humile) or
Pheidole megacephala were placed in contact with a colony of
Anoplolepis gracilipes, the workers
and queens of A. gracilipes were always destroyed and the brood was taken as food by the other ant. A. gracilipes seemed to make no effort to defend itself or the brood. Instead the workers would run about the enciosure in panic and most would be killed by running into the "Tanglefoot" barrier rather than in fights with the other ants.
Colonies of Argentine ants and Pheidole which had been maintained in the laboratory for three weeks were put together so that there was continuous contact along one side of the nest platforms. Within ten minutes, the
whole colony of Argentine ants had crossed over to the
Pheidole platform. This invasion included not only
workers but the brood and many queens as well.
There seemed to be no concentrated attack by the
Argentine ants; however, there were chance encounters
caused by the Argentine ants scurrying about. An occasional
Argentine ant would go into the area where the
Pheidole colony was concentrated. It would be immediately
attacked by one or more Pheidole workers and usually would be killed.
The only unusual excitement in the Pheidole nest was caused by the
occasional invasion by an
Argentine ant. However, there seemed to be a response to
the invasion throughout the Pheidole colony whereby the
Pheidole began to seal the entrances to the nest with
trash as a protective measure.
In less than 90 minutes, the Argentine ants had moved
all their brood and queens back into their original colonies
with only an occasional Argentine ant venturing onto
the Pheidole platform. when an Argentine ant would cross over
to the other platform, it would only go to the outer perimeter.
After four hours, there was no sign that either ant
would attack the other in sufficient numbers to eliminate
the colony. The Argentine ants still moved about their
platform in the usual foraging manner, occasionally crossing over
to the Pheidole piatform. The Pheidoe were
still in the process of sealing the entrances to their
nest. There were a few soldiers ani workers of PheidoZe
on the Argentine platform.
At five hours after beginning the experiment, the
Argentine ants began moving their brood from one nest to
another. In a short time the colony became very excited
and started moving the brood out of both nests and eventually
setitied down at the opposite end of the platform
from the nests. This excitation of the colony seemed to
have been preceded by the invasion of the Argentine ant
colony by four or five Phetdote soldiers, The Argentine
ants seemed to go out of their way to avoid contact with
the soldiers, : even when the soldiers were injured.
Pheidole soldiers are much slower in their movements than
the Argentine ant workerss; but they snap their mandibles
at any moving object whichi near They will do this to
even their own species when they are very excited.
After a 12 hour period had elapsed, the Argentine ant
colony was still grouped with their queens and brood at
the corner of the platform farthest from the nests. After
the lights in the laboratory had been on for five to
ten minutes, the Argentine ants began to move back into
the two nests. Within a period of ten minutes, they
had moved al1 of their brood back into the nests.
At this time there was very little disturbance of the
Argentine ant colony by Pheidole.
At 24 hours from the beginning of the experiment,
the complete Argentine ant colony had moved again. This
time they moved from the nests into the corner farthest from the Pheidole and their own nests. At this point
in time, the former Argentine ant nests were occupied by
six to ten Pheidole soldiers and approximately fifteen
workers in each nest. The Argentine ants appeared to be
very sluggish in their movements and were making no attempt to
re-establish themselves in their nests. Even when a
75-watt 1ight was turned on directly above them, no attempt
was made to protect themselves or their brood from the light. The colony of Pheidole seemed to be engaged in
its normal activities without undue excitement,
Late in the morning of this second day of observations, another
artificial nest was put on the platform
containing Argentine ants. The colony immediately began
moving into the nest. In less than 20 minutes the entire
colony of Argentine ants was inside the nest.
Approximately four hours later, the colony of Argentine
ants was still in the new nest with the Pheidole occupying
the original Argentine ant nests.
At eight o clock in the morning of the following day,
it was observed that the Argentine ants had moved out of
the new artificial nest and were on top and to one corner
of the nest. Shining bright lights on the colony did not
force them to move. Only one Pheidole was seen in the
nest which the Argentine ants had vacated.
The experiment explained above was repeated in the
laboratory four times. Each experiment ended with
Pheidole having possession of the nests and the Argentine
ants huddled in a corner as far away from Pheidole as they
could possibly get.
A later experiment consisted of placing a small colony of
Argentine ants in an artificial nest with sand
completely covering the floor of the platform to a depth
of one-half inch. This platform was connected to another
platform containing a very large colony of Pheidole. The
Argentine ants immediately began to cross over to the
Pheidole platform. There were so many Pheidole at the
base of the bridge that the Argentine ants were unsuccessful
in crossing over to the other platform. When one
would try to make the crossing, it would be immediately
attacked by Pheidole soldiers and workers. This situation was
observed for one hour. The following morning, it was
noted that the complete colony of Argentine ants had been
killed by the Pheidole ants. The nest which had been
originally occupied by the Argentine ants was inhabited
by Pheidole. Upon close examination, it was observed
that numerous Pheidole workers were carrying brood to
their original nests. It was determined that this was
the Argentine ant eggs, larvae and pupae which were
probably used as food by the Pheidole colony.
In efforts to establish Argentine ants in the ant infested
plots of sugarcane at the Waimanalo Experiment
Station, two large colonies of Argentine ants were brought
from Wailua Agriculture Company Field Opaeula Number Nine
to the Waimanalo plots. The ants were transported from Wailua
to Waimanalo in heavy plastic bags The two plastic bags
containing the ants were placed at the edge of
the plot and a hole was punched in each bag. This hole
was made to allow the insertion of a sugarcane leaf into
the bags. The leaf was positioned so that the ants would
move along the leaf to a horizontal cane stalk which was
lying on the ground. Some loose soil had been previously
placed over a portion of the stalk about three feet from
the plastic bags as a possible nest. The ants immediately
began moving their brood from the plastic bags to the place
where the soil was covering the stalk. By close
observation, it was noted that the workers would take
the brood to the soil covering the stalk and return to
the plastic bags for more brood.
During six hours of almost constant observation,
there was a steady stream of workers with brood going to
the new nest from the plastic bags and returning empty
to the bags after more brood. At the end of six hours,
it was noticed that some Pheidole soldiers and workers
were at the base of the sugarcane stalk approximately
two feet from the nest. At the same time large numbers
of Pheidole soldiers and workers were observed on the
ground about one foot from the Argentine nest. Within
four hours after the first Pheidole was seen in the vicinity
of the Argentine ant nest, the Pheidote ants had moved into
the Argentine ant nest with the result that the
Argentine ants had moved their brood out of the nest and
through an area which had been treated with 2.58 Dieldrin
granules. The Argentine ants moved even though they outnumbered
the Pheidole tremendously. There were close to ten
thousand Argentine workers in the nest and less than one
hundred Pheidole near the area.
Argentine ants were introduced to the Waimanalo
Experiment Station plots on several occasions prior to
this using similar methods. Each time they disappeared,
so this particular attenpt was made to determine their
actions and movements.
The behavior exhibited by Pheidole and the Argentine
ants suggests that glandular secretions are involved and
play a large role in the behavior on one ant toward the
other. Crowell (1968) theorized that the Argentine ant
released some type of glandular secretion which was very
repugnant to Pheidole, causing Pheidole to move away from concentrations of Argentine ants. If indeed there is a
chemical repellent released by the Argentine ants, my
studies seem to indicate that only under certain conditions
do the Argentine ants release this glandular secretion.
This appears to be during the time immediately
preceding an invasion of new territory by the Argentine
ants. If a glandular secretion is produced by the
Argentine ants, this could account for the "Buffer Zone"
that is commonly found separating the Argentine ants and
Pheidole during the former's "invasion cycle". At other
times, Argentine ant and Pheidole colonies are found very
close together.
The studies conducted in the laboratory and sugarcane
plots at Waimanalo Experiment Station appear to indicate
that the Pheidole soldier may release a glandular secretion
that is offensive to the Argentine ants. The action
of the Argentine ant in the presence of the Pheidole soldier
suggests this possibility. Although the Argentine
ants will attack and kill Pheidole workers and will continue
to mutilate their bodies after death, the Argentine
ants appears to go to great extremes to avoid a Pheidole
soldier. Even if the Argentine ants far outnumber the
Pheidole soldiers, they will make no attempt to attack.
No attempt was made to determine if the Pheidole soldier
has a glandular secretion that was responsible for the
actions of the Argentine ants. However, I find it difficult
to believe that the mere physical presence of a few
Pheidole soldiers is all that is needed to cause a colony
of thousands of Argentine ants to abandon otherwise suitable nesting sites.