red imported fire ant infestation continues to expand, partially as a
result of recent mild winters but more recently due to increased residential and industrial development and subsequent introductions of fire ants in infested sod and nursery stock. Although fire ant stings are
not fatal for most people, they are painful. The mounds that the ants
build can interfere with the operation of machinery in agricultural
fields. It is not practical to eradicate these ants, but their populations
can be controlled, and the chance of contact with people can be minimized.
This publication discusses the red imported fire ant and suggests suitable
The red imported fire ant, Solenopsis invicta, a native of southern
Brazil, currently inhabits eleven
southern states, as well as isolated areas in New Mexico and California.
In North Carolina, imported fire ant is found in 71 of 100 counties including isolated areas in western NC. These areas
(shown in red on this map). These areas are currently under quarantine by the U.S.
Department of Agriculture (USDA) and the North
Carolina Department of Agriculture & Consumer Services (NCDA&CS),
regulating the export
of certain items that might carry ant infestations to other parts
of the country.
Even if you are not currently in
a quarantined area, you should be aware of how fire ants will affect you
and how you can control them because North Carolina�s fire ant infestation
is expanding into counties adjacent to the quarantine zone. The ants expand
naturally and steadily into new territory because of their high reproductive
rate; mild winter weather has accelerated their movement. Current technology
and control efforts are not expected to reverse this growth trend in the foreseeable
future. In addition, long-distance movement often occurs because of
human activities, primarily through the transport of fire-ant-infested nursery
plants and sod into areas outside of the federal and state quarantine
zone. The NCDA conducts yearly surveys to detect the spread of fire ants
and adjusts the established quarantine zone accordingly.
From an agricultural
perspective, red imported fire ants are nuisances primarily because
they annoy field workers and because their mounds may damage harvesting
equipment. Livestock injury and crop damage are usually minor. Fire
ants have a much greater impact on the orna-mental plant, sod, and landscaping
industries because of problems associated with shipping infested plant
material into uninfested areas of the country (see the section entitled
Mounds discovered in previously uninfested areas of North Carolina are frequently traced to landscaping performed at commercial and residential
developments. For the general public, two aspects of red imported fire
ant infestations are particularly annoying: the unsightly mounds formed
in lawns and yards and the painful stings received when mounds are disturbed.
Within 24 hours after a person is stung, a pustule-like sore forms at
each sting site (as shown here), which usually itches intensively. Scratching
the pustule may rupture the skin, leading to secondary infection and
scarring. A small proportion of people stung is highly allergic to
fire ant stings and requires immediate medical attention. As red imported
fire ants spread into more populated areas of the state, more people
are likely to be stung. Encounters with fire ants can be expected not
only outdoors but indoors as well. In other southern states foraging
ants have invaded private residences and buildings such as offices,
hospitals, and nursing homes. In these situations, fire ant control
is more critical and potentially more difficult because of concerns
related to both the ants and the indoor use of chemical insecticides.
red imported fire ants are reddish to dark brown and occur in five forms:
(1) minor workers, about 1/8 inch long;
(2) major workers, about 1/4 inch long;
(3) winged males and (4) females, each about 1/3
inch long; and (5) queens, about 1/3
inch long. Fire ant mounds vary in size but are usually in direct proportion
to the size of the colony. For example, a mound that is 2 feet in diameter
and 18 inches high may contain about 100,000 workers, several hundred
winged adults, and one queen. If you break open an active fire ant mound, you typically find the "brood" - whitish rice grain-like larvae and pupae. These immature ants will eventually
develop into workers or winged adults. Mounds constructed in clay soils
are usually symmetrical and dome-shaped; mounds
built in sandy soils tend to be irregularly shaped. It is often difficult
to distinguish the red imported fire ant from the tropical fire ant
and the southern fire ant, which are also found in North Carolina. For
positive identification, take a specimen to your county Cooperative
During the spring
and summer, winged males and fe-males leave the mound and mate in the
air. After mating, females become queens and may fly as far as 10 miles
from the parent colony. However, most queens descend to the ground within
much shorter distances. Only a very small percentage of queens survive
after landing. Most queens are killed by foraging ants, especially
other fire ants. If a queen survives, she sheds her wings, burrows into
the ground, and lays eggs to begin a new colony. In the late fall, many
small colonies of fire ants will appear. Many of the colonies will not
survive the winter unless the weather is mild.
Fire ants prefer oily and greasy foods. They also feed on many other insects and, from that standpoint, could be considered beneficial. To find food, workers forage around their mound often in underground tunnels that radiate from the mound. If the mound is disturbed, ants swarm out and sting the intruder.
Click on image to see pictures of a typical
fire ant colony
Fire ant mounds are typically found in
receive direct sunlight
Mound in clay soil have more of a dome shape.
Mound in sany soils are often more irregular.
ants cannot be eradicated over wide areas, the goal should be to manage the ants with a combination of chemical and non-chemical control tactics in order to eliminate fire ants in areas where they pose the most immediate hazard to people, pets and livestock,
and to reduce infestations to "acceptable" levels. Options for control depend on the setting (e.g., agricultural fields, pastures, home lawns, schools, etc.).
As with any other insect pest, fire ants spend a great deal of time searching for food. That foraging activity can bring them inside buildings. You can reduce ant foraging around buildings by eliminating available food sources in these areas.
Inspection and Observation
Because fire ants can be spread in new landscape material such as shrubs, sod, wheat and pine straw, check these items carefully before you purchase them or have them installed. If you are doing your own landscaping there is a chance you could get stung while handling fire ant infested items. If you find fire ants in plants, sod, pine straw or wheat straw, contact the supplier immediately.
two basic approaches to chemical control of fire ants. An insecticide
can be applied to individual mounds or it can be broadcast over a wide
area infested with fire ant colonies. Individual mound treatments are
usually more environmentally and ecologically acceptable because they
use less insecticide and limit areas treated as compared to broadcast treatments, and they are likely to have less impact on non-target insects. Regardless
of the method used, the objective is to kill not only the workers but also the queen, because she
is the only ant in the colony that is capable of laying eggs. Always follow the label directions when applying any fire ant insecticide.
mounds may be treated with a liquid or dust insecticide formulation or with an insecticidal
Liquid treatments may be done by rodding the chemical deep into the mound (as seen in the image to the right) or by drenching the mound. To be effective, the drench must
trickle down through the mound and contact most of the fire ants in the colony. Ants
contacted by the drench die in less than 24 hours. Drenches are the preferred treatment when the risk of human contact with fire ants is high and the fire
ant infestation must be eliminated immediately because of the health risks of someone getting stung. High-risk areas include
home lawns, school grounds, parks, and other areas frequently used by
the public. Best control results are usually obtained in spring and
fall when temperatures are between 70oF and 85oF.
Control with drench treatments is more difficult to achieve during very
hot summer months because the ants remain deep within their mounds and
are hard to reach with liquid insecticides. In the summer, drenches are best done in the morning or evening. The following procedure
is recommended for drenching mounds. Contact your county Cooperative
Extension Center or consult the NC Agricultural Chemicals Manual for information on fire ant insecticides appropriate for use by
the general public
public health and pest management professionals
Following label directions, pour the correct amount of water into a
bucket or sprinkler can. Add the prescribed amount of insecticide, mix
well (without splashing), then gently pour the diluted insecticide over
the surface of the mound. Apply the drench at a rate of approximately
1 gallon per 6 inches of mound diameter. At this rate, for example,
a mound measuring 12 inches across would receive 2 gallons of insecticide
drench. The amount of drench applied is more important than the concentration
of insecticide in the drench. Thoroughly wet the ground to a distance
of about 2 feet around the mound. Sometimes the drench does not
kill all fire ants in a treated colony. The surviving ants will construct
small mounds within 10 to 15 feet of the parent colony. Several days
after the application, search the area around the treated colony for
new mounds and treat them with the insecticide drench. Keep children
and pets away from the treated area until it is dry (or as designated
on the pesticide label).
baits also can be used to treat individual mounds. These baits are essentially a mixture of an insecticide
and a food that is attractive to fire ants. Worker ants carry particles
of the bait back to the mound and feed them to the "brood" (larvae or immature ants) and the queen. Even when the
insecticide kills the queen, workers may be active inside the mound
for several weeks before the colony finally disappears. Baits are somewhat
slow acting but easier to apply than mound drenches. Therefore, they
are best used in situations where many mounds must be treated, or when
water for mixing mound drenches is difficult to obtain,
or when the risk of human or non-target animal contact is low and there
is no urgent need to eliminate the infestation. The active ingredients
in ant baits are rapidly degraded by high temperature, high humidity,
and intense sunlight. The baits can be rendered ineffective in a few
hours by these conditions. Follow this procedure when using baits.
"Two-Step Method" - You can also apply a mound drench 5-7 days after baiting to kill of remaining workers more quickly.
treatments can be used to apply insecticides (liquids, baits, or granular insecticides)
over a large infested area containing many fire ant colonies. One disadvantage
of broadcast treatments is that they can also disrupt ant communities. Although most people think of ants strictly as being pests, they are also a very important parts of our ecosystem. Broadcast treatments can result in an ant community
changing from one that is dominated by native ants to one dominated by
imported fire ants. On the other hand, in areas with very high mound densities,
broadcast applications allow large areas to be treated quickly. Areas
of high public use may be protected by spring and fall broadcast applications
of ant bait or a well-timed granular insecticide. One limitation on the use of granular insecticides (not granular baits) is that most of them require water (either from rain or by irrigation) to be applied shortly after the application. When rain is not expected for several days or in areas where watering may be restricted or not feasible, a granular insecticide may not be the best choice. If the area becomes reinfested with fire ants during the
summer months, individual mounds can be treated with an insecticide drench
or ant bait, although as noted previously control is more difficult when
temperatures are high. Consult the
NC Agricultural Chemicals Manual
for a list of granular insecticides (and baits) that can be used against
The key to reducing the threat
of fire ant infestations indoors is prevention, which means removing exposed
food sources that may attract these insects. In some cases, fire ants may nest indoors, e.g., inside walls or partially under concrete slab floors. In those instances you will likely see soil and other debris pushed out around expansion joints near the edge of carpeting (image at right) or around water or other utility pipes. In most situations, fire ants are simply entering the building from an outdoor nest. In those situations, the treatment objective must be to reduce the potential for accidental
stings as quickly as possible. Insecticides labeled for indoor use can be found in
NC Agricultural Chemicals Manual
. Particularly the pyrethroid insecticides (products containing chemicals such as permethrin, cyfluthrin, bifenthrin, etc.),
can be used in homes and public buildings to drive foraging ants outside
or away from high-use or critical areas, such as kitchens, recreation
rooms, patient rooms, operating rooms, or intensive care units. Select products that are specifically labeled for use indoors. Although
baits work well for many ant species that invade buildings, they are not the best choice for controlling fire ants indoors because they are more likely to draw more ants inside and potentially increasing the chance that someone will be stung.
For this reason, it is important to positively identify the ants that are invading your home before applying any control measures. Information about other ant species can be found in A Guide to House-Invading Ants and Their Control.
control of fire ants that invade indoor areas can be achieved only by locating and then treating
outdoor mound(s) using the methods explained above.
A good summary of fire ant
control products available for use by the general public can be found in this publication from Auburn University. Options for control are more restricted for areas such as pastures that may be used for grazing horses or livestock. Consult the following publications for advice in dealing with these situations:
Fire Ant Management in Pastures
Fire Ant Management in Horse Operations
NON-CHEMICAL CONTROL OF FIRE ANTS
There are some non-chemical methods available that
can be used against fire ants; however, they may be limited in their effectiveness (or may be ineffective).
Hot Water and Mechanical Disruption
QUARANTINE INFORMATION & ASSISTANCE FOR NURSERY CROPS
Since the major sources of new infestations outside the current fire ant range are often infested sod and nursery stock, limiting this source or ants is critical to slowing the spread of fire ants.
The North Carolina
Department of Agriculture & Consumer Services and the USDA-Animal and Plant
Health Inspection Service (USDA-APHIS) cooperatively regulate shipments
of nursery and sod farm items, such as balled nursery stock and turf,
to areas outside of the quarantine zone. Under the terms of the compliance
agreement, nursery operators have several ways to obtain certification
and to ship nursery stock out of the quarantine zone. For information
and assistance, contact the NCDA&CS.
NCDA&CS Imported Fire Ant Regulations
Fire Ant Information for Nurseries & Plant Growers
Pest information and control
recommendations presented here were developed for North Carolina and may
not be appropriate for other states or regions. Any recommendations for
the use of chemicals are included solely as a convenience to the reader
and do not imply that insecticides are necessarily the sole or most appropriate
method of control. Any mention of brand names or listing of commercial
products or services in the publication does not imply endorsements by
North Carolina Cooperative Extension nor discrimination against similar
products or services. All recommendations for pesticide use were legal
at the time of publication, but the status of pesticide registrations
and use patterns are subject to change by actions of state and federal
regulatory agencies. Individuals who use chemicals are responsible for
using these products according to the regulations in their state and to
the guidelines on the product label. Before applying any chemical, always
obtain current information about its use and read the product label carefully.
For assistance, contact the Cooperative
Extension Center in your county.
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of the acts of Congress of May 8 and June 30, 1914. North Carolina State
University and North Carolina A&T State University commit themselves
to positive action to secure equal opportunity regardless of race, color,
creed, national origin, religion, sex, age, or disability. In addition,
the two Universities welcome all persons without regard to sexual orientation.
North Carolina State University, North Carolina A&T State University,
U.S. Department of Agriculture, and local governments cooperating.