The ARGENTINE ANT, LINEPITHEMA HUMILE (formerly
is an ant native to northern
Paraguay , Bolivia
Brazil . It is an invasive species that has been
established in many
Mediterranean climate areas, inadvertently
introduced by humans to many places, including South Africa, New
Easter Island , Australia, Europe, Hawaii, and the
continental United States.
* 1 Description
* 2 Distribution
* 2.1 Global "mega-colony"
* 3 Behavior
* 4 Reproduction and seasonal colony trends
* 5 Impact
* 6 Pest control
* 7 References
* 8 External links
The worker ants are 1.6–2.8 millimetres (0.06–0.11 in) long and
can easily squeeze through cracks and holes as small as 1 millimetre
(0.04 in) in size. Queens are 4.2–6.4 millimetres (0.17–0.25 in)
long, much smaller than other species of ants. These ants will set up
quarters in the ground, in cracks in concrete walls, in spaces between
boards and timbers, even among belongings in human dwellings. In
natural areas, they generally nest shallowly in loose leaf litter or
beneath small stones, due to their poor ability to dig deeper nests.
However, if a deeper nesting ant species abandons their nest,
Argentine ant colonies will readily take over the space. Typical
size of worker ants found in Southern California. These markers
can help identify Argentine ants.
German entomologist Gustav L. Mayr identified the first specimens of
Hypoclinea humilis in the vicinity of
Buenos Aires ,
1866. This species was shortly transferred to the genus
and finally to
Linepithema in the early 1990s.
The native range of Argentine ants is limited to around major
waterways in the lowland areas of the
Paraná River drainage. They
have recently spread into parts of Argentina, Brazil, Chile, Colombia,
Ecuador, and Peru. The species has become established in at least 15
countries throughout the world, on six continents, as well as many
According to research published in
Insectes Sociaux in 2009, it was
discovered that ants from three
Argentine ant supercolonies in
America, Europe, and Japan, that were previously thought to be
separate, were in fact most likely to be genetically related. The
three colonies in question were one in Europe, stretching 6,000 km
(3,700 mi) along the
Mediterranean coast, the "Californian large"
colony, stretching 900 km (560 mi) along the coast of
California , and
a third on the west coast of
Based on a similarity in the chemical profile of hydrocarbons on the
cuticles of the ants from each colony, and on the ants' non-aggressive
and grooming behaviour when interacting, compared to their behaviour
when mixing with ants from other super-colonies from the coast of
Catalonia in Spain and from
Kobe in Japan, researchers concluded that
the three colonies studied actually represented a single global
The researchers stated that "enormous extent of this population is
paralleled only by human society", and had probably been spread and
maintained by human travel.
Argentine ants on a dead horse-fly
They have been extraordinarily successful, in part, because different
nests of the introduced Argentine ants seldom attack or compete with
each other, unlike most other species of ant. In their introduced
range, their genetic makeup is so uniform that individuals from one
nest can mingle in a neighboring nest without being attacked. Thus, in
most of their introduced range, they form supercolonies . "Some ants
have an extraordinary social organization, called unicoloniality,
whereby individuals mix freely among physically separated nests. This
type of social organization is not only a key attribute responsible
for the ecological domination of these ants, but also an evolutionary
paradox and a potential problem for kin selection theory because
relatedness between nest mates is effectively zero." The Very Large
Colony, which covers territory from San Diego to beyond San Francisco,
may have a population of nearly one trillion individuals.
Conflict does occur between members of different supercolonies. In
1997, UC San Diego researchers observed fighting between different
Argentine ants kept in lab, and in 2004 scientists began to map out
the boundaries of the different supercolonies that clashed in San
Diego. On the border of the Very Large Colony and the Lake Hodges
Colony thirty million ants die each year on a battlefront that covers
In contrast, native populations are more genetically diverse,
genetically differentiated (among colonies and across space), and form
colonies that are much smaller than the supercolonies that dominate
the introduced range. Argentine ants in their native South America
also co-exist with many other species of ants, and do not attain the
high population densities that characterize introduced populations.
In a series of experiments, ants of the same colony were isolated and
fed different diets. The hydrocarbons from the diet were eventually
incorporated into the cuticle of the subjects. Those that had the same
diet appeared to recognize one another as kin. Those who had at least
some overlap in dietary composition also appeared to react
non-aggressively to one another. These interactions contrasts
drastically with the groups that fed on completely different sources,
such as those who lived off flies and those that fed on grasshoppers.
The groups appeared to have incorporated hydrocarbons that were not
similar to the others and created an unfamiliar identity cue. These
groups reacted violently towards each other. This suggests that
dietary factors affect the recognition cues for colony members.
REPRODUCTION AND SEASONAL COLONY TRENDS
Like workers in many other ant species,
Argentine ant workers are
unable to lay reproductive eggs but can direct the development of eggs
into reproductive females; the production of males appears to be
controlled by the amount of food available to the larvae. Argentine
ant colonies almost invariably have many reproductive queens, as many
as eight for every 1,000 workers. The queens seldom or never disperse
in winged form. Instead, colonies reproduce by budding off into new
units. As few as ten workers and a single queen can establish a new
The seasonal low occurs in mid-winter, when 90% of a representative
colony consisted of workers and the remainder of queens, and no
reproductive activity and minimal birthing. Eggs are produced in
late-winter, nearly all of which hatch into sexual forms by May.
Mating occurs after the females emerge. Worker production increases
steadily from mid-March to October, after which their numbers are not
replenished; thus, their numbers drop steadily over the winter months.
Colonies in the Argentine ant’s native habitat are kept within a
range of ten to one hundred meters by colonies of interspecific and
intraspecific rivals. As the colonies expand, they appear to form
fluctuating territory borders, which contract and expand on a seasonal
and conditional basis. There is an expansive push outward in the
summer months, with a retreating motion in the winter. This has to do
with soil moisture and temperature conditions. At the edges of these
borders are either rival L. humile colonies or other obstacles that
prevent further expansion, such as an inhospitable environment for
The ants are ranked among the world's 100 worst animal invaders. In
its introduced range, the
Argentine ant often displaces most or all
native ants. This can, in turn, imperil other species in the
ecosystem, such as native plants that depend on native ants for seed
dispersal, or lizards that depend on native ants for food. For
example, the recent severe decline in coastal horned lizards in
California is closely tied to Argentine ants displacing
native ant species on which the lizards feed.
Argentine ants sometimes tend aphid colonies, and their protection
of this plant pest from predators and parasitoids can cause problems
in agricultural areas. In return for this protection, the ants
benefit by feeding off an excretion known as honeydew . Thus, when
Argentine ants invade an agricultural area, the population densities
of these plant parasites increase and so does the damage they cause to
Argentine ants accessing a commercial bait station commonly
available in the United States
Argentine ants are a common household pest, often entering structures
in search of food or water (particularly during dry or hot weather),
or to escape flooded nests during periods of heavy rainfall. When they
invade a kitchen, it is not uncommon to see two or three queens
foraging along with the workers. Eliminating a single queen does not
stop the colony's ability to breed.
Borate-sucrose water baits are toxic to Argentine ants, when the bait
is 25% sucrose water, with 0.5-1.0% boric acid or borate salts.
Due to their nesting behavior and presence of numerous queens in each
colony, it is generally impractical to spray Argentine ants with
pesticides or to use boiling water as with mound building ants.
Spraying with pesticides has occasionally stimulated increased
egg-laying by the queens, compounding the problem. Pest control
usually requires exploiting their omnivorous dietary habits, through
use of slow-acting poison bait (e.g. fipronil , hydramethylnon
sulfuramid ), which will be carried back to the nest by the workers,
eventually killing all the individuals, including the queens. It may
take four to five days to eradicate a colony in this manner.
Researchers from the
University of California, Irvine
University of California, Irvine , have
developed a way to use the scent of Argentine ants against them. The
exoskeletons of the ants are covered with a hydrocarbon-laced
secretion. They made a compound that is different, but similar, to the
one that coats the ants. If the chemical is applied to an ant, the
other members of the colony will kill it. The chemical method may be
effective in combination with other methods.
Another approach for a large scale control of the
Argentine ant has
been proposed by researchers from Japan, who showed that it is
possible to disrupt its trails with synthetic pheromones . This has
been confirmed in various later trials by a New Zealand-led team in
Hawaii and by researchers from
Victoria University of Wellington who
showed that this approach is beneficial for other local ant species.
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