Potentially Misidentified Species:
Florida is home to two different species of fire ant. In addition to the
ubiquitous non-native red imported fire ant (Solenopsis invicta), Florida is
also home to the less frequently encountered native tropical fire ant, S.
geminata. Drees (1997) notes that S. geminata mounds can be distinguished by
the presence of workers with disproportionately large square heads that are
lacking in S. invicta worker ants.
A number of other fire ants of genus Solenopsis occur in the United States,
including the black imported fire ant, Solenopsis richteri. Introduced to the U.S. in
1918, Solenopsis richteri co-occurs with S. invicta within a portion of its non-native
distribution in the U.S. (e.g., Mississippi and western Georgia) and is capable
of hybridizing with S. invicta (ARS 2003, Collins and Scheffrahn 2005).
There are more than 280 species of Solenopsis worldwide.
II. HABITAT AND DISTRIBUTION
S. invecta is a southern South American species native to Brazil.
It was likely introduced to the United States in the 1920s and
1930s and to parts of Australia in the 1970s. The species
has also become established in New Zealand, Puerto Rico, and the
Virgin islands. S. invecta now infests more than 320 million
acres in 12 states in the southeastern U.S. and Puerto Rico.
The species has also recently been reported from California and New
Mexico (Holway et al. 2002, ARS 2003).
S. invicta occurs throughout the entire state of Florida, including
all six counties within the IRL watershed.
III. LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan:
Solenopsis invicta is a small ant, with workers averaging 3-6 mm in length.
Vinson & Sorenson (1986) report that a mature S. invicta colony
can have nearly one-quarter million workers while typical colonies
have about one-third as many. These authors also estimate that in
the southern U.S. where S. invicta occurs, nearly 100,000 new
queens per year can be produced in every acre of infested land.
Winged reproductive males called alates are produced once a colony is a
year old. As many as 4,500 alates join winged reproductive female
alates (the new queens) to take part in a mating flight during
which the females are fertilized in the air. The males die
shortly thereafter and the fertilized females establish new colonies.
Six and eight mating flights in the spring and fall months are typical for mature colonies(Vinson and Sorenson 1986,
Collins and Scheffrahn, 2005).
Newly mated queens will often cluster together in sheltered areas
after mating and may cooperate to establish a new colony. Vinson
and Sorenson (1986) indicate that multiple-queen S. invicta
colonies do occur in some cases, while in other cases all but one
queen will die off as the colony matures (Collins and Scheffrahn,
After mating, a female alate will lose its wings and locate a suitable spot for
a new colony. After burrowing into the soil and sealing herself into a self-excavated chamber, the young queen will lay an initial clutch of usually
10-15 eggs. These will hatch into the first cohort of sterile female workers
in 8-10 days, during which time the queen will have produced on the order of
100 more eggs (Holldobler and Wilson 1990, Collins and Scheffrahn 2005).
As with most insects, S. invicta early life history includes both a
larval and a pupal stage. Larvae are the immature, wormlike first feeding
forms that emerge from the eggs and pupae are subsequent quiescent stage prior
to metamorphosis. In S. invicta each of these stages persists for
approximately 1-2 weeks, and the initial cohort of worker ants becomes mature
2-4 weeks after hatching. Until this first clutch grows to maturity, the young
queen will refrain from laying more eggs. The queen provides nutrition to the
first batch of developing young in a number of ways, including the production
of non-developmental trophic eggs, regurgitation of energy-rich oil, salivary
secretions, and via breakdown of the now-unneeded wing muscles. All of these
sources of nutrition are used to provide nutrients to larvae and pupae of this
initial clutch (Vinson & Sorenson 1986, Collins and Scheffrahn 2005). Because
the young queen can provide only limited nutrition these initial workers are
notably smaller when they emerge than are successive cohorts. On emerging,
however, this group of workers sets to work foraging for food for the queen and
the next generation of larvae.
Low temperatures appear to be key to limiting northward expansion
of the range of Solenopsis invicta in the United States. Ecological
models predict that the species will fail to become established in
regions where the soil persists at near-freezing temperatures for
more than a couple of weeks (ARS 2003).
V. COMMUNITY ECOLOGY
Solenopsis invicta is a predatory ant species whose diet consists primarily of
small invertebrates such as insects and spiders, centipedes and millipedes,
earthworms, and other similarly sized prey. S. invicta also regularly consumes
carrion and are attracted to sugary substances. Food is collected by foraging
worker ants who use pheromone trails to direct one another to food sources once
they have been located (USDA 1993).
VI. INVASION INFORMATION
The Agricultural research Service reports that red imported fire ants were accidentally
introduced into the United States from South America, likely in the late 1920s
(ARS 2003). The precise introduction pathway is unknown, but one possibility is
that the ants were accidentally transported into the U.S. along with potted
In the absence of their natural predators, competitors and parasites to keep the
species in check, RIFA have become five times as abundant in
North America as they are in South America. Since the initial introduction of
the species, Solenopsis invicta has expanded its range to include a significant portion
of the southeastern United States.
Potential to Compete With Natives:
Fire ants are capable of causing dramatic reductions in the numbers of native
ant populations and a variety of ground-nesting animals (ARS 2003). Allen et
al. (1995) report negative impacts of S. invicta on populations of
northern bobwhite (Colinus virginianus).
Possible Economic Consequences of Invasion:
RIFA are responsible for extensive crop damage as well as damage to electrical
and other equipment. The Agricultural Research Service has estimated the
annual costs in terms of damage and population management control at more than
$6.5 billion (ARS 2003).
S. invicta has been nominated by the Invasive Species Specialist Group
(ISSG) as among "100 of the World's Worst" invasive alien species.
Agricultural Research Service (ARS). 2003. Update: Hot on the trail of fire
ants. Published in Agricultural Research Magazine, Vol. 51.
Allen C.R., Lutz R.S., and S. Demarais. 1995. Red imported fire ant impacts on
northern bobwhite populations. Ecological Applications 5:632-638.
Cohen P.R. 1992. Imported fire ant stings: clinical manifestations and
treatment. Pediatric Determology 9:44-48.
Collins L., and R.H. Scheffrahn. 2005. Red imported fire ant, Solenopsis
invicta Buren (Insecta: Hymenoptera: Formicidae: Myrmicinae). UF/IFAS
document EENY-195. Published: January 2001. Revised: August 2005.
Drees B.M. 1997. We're all on the same team when tracking fire ants. Available
Hedges S.A.1997. Fire ants. Pp. 531-535 in: D. Moreland (Ed.). Handbook of
Pest Control, 8th Ed. (Mallis Handbook and Technical Training Company.
Holldobler B., and E.O. Wilson. 1990. The Ants. 165 p. The Belknap Press of
Harvard University Press, Cambridge, MA.
Holway D.A., Lach L., Suarez A.V., Tsutsui N.D., and T.J Case. 2002. The causes
and consequences of ant invasions. Annual Review of Ecology and Systematics
USDA. 1993. Fact sheet for the two species of imported fire ant: red imported
fire ant Solenopsis invicta, black imported fire ant Solenopsis
richteri. Document FACTS-03 PPQ.
Vinson S.B., and A.A. Sorensen. 1986. Imported fire ants: Life history and
impact. Texas Department of Agriculture. Department of Entomology, Texas A and
M University. College Station, TX.
J. Masterson, Smithsonian Marine Station
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Page last updated: October 4, 2007