Control of Argentine Ants and Odorous House Ants in the Home
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Control of Argentine Ants and
Odorous House Ants in the Home
Although several species of ants of an inch long, do not have a
will invade homes in Mississippi, sting, and are light brown or brown
Argentine ants and odorous house in color. Although there are distinct
ants are, by far, the two most com- differences that can be seen easily
monly encountered species. Both under a microscope, these are diffi-
are primarily outdoor species that cult to see without magnification.
go largely unnoticed by homeown- One way to tell the difference
ers until they invade homes and between these two ants is by the
begin raiding pantry shelves. smell of freshly crushed workers.
To the untrained eye, Argentine Argentine ants have a stale, musty
ants (Figure 1) and odorous house odor, while the smell of odorous
ants (Figure 2) look similar. Workers house ants often is compared to that
of both species are about one-tenth of rotten coconuts.
Figure 1. The Argentine ant, Linepithema humile
(Mayr), lateral view of a worker. Note the single,
pointed node between the thorax and abdomen.
The scale bar equals 2 mm (about 1/12 inch).Because Argentine ants
tend to displace other ant
species, odorous house ants
are less common in areas
infested with Argentine
ants. Another species that
occasionally invades homes,
the little black ant, could be
confused with these two
ants, but it is smaller and
shiny-black in color. The
little black ant also moves
more slowly than the other
two ants.
Odorous house ants
and Argentine ants are
difficult to control, with
Argentine ants being espe- Figure 2. The odorous house ant, Tapinoma sessile
cially challenging. Unfor- (Say), lateral view of a worker. Note the single, flat-
tened node between the thorax and abdomen. The
tunately, there is no single, scale bar equals 2 mm, or about 1/12 inch.
simple means of controlling
these ants, and effective
control requires using a combination of but the bite is not very painful. When work-
several methods. A basic understanding of ers of this species are disturbed or freshly
the biology and habits of these pests will crushed, they emit a stale, musty odor.
give you a better chance of successfully Nest sites may consist of little more than a
controlling them. moist, protected area where eggs, larvae, and
pupae are kept in piles and tended by work-
ers. Unlike fire ants, Argentine ants do not
Argentine Ants
nest in single, easily recognized—and, there-
The Argentine ant is one of the most per-
fore, easily treatable—nest sites. Instead, a
sistent and troublesome of the house-infest-
single colony will have many different nest
ing ants. This species, known by the scientific
sites, connected by trails. These nest sites
name of Linepithema humile (Mayr), was intro-
normally are hidden and difficult to detect.
duced to the United States from Brazil and
A colony may consist of tens of thousands of
Argentina in the late 1800s. It is now well
workers and hundreds of reproductive
established through much of Mississippi and
queens. Despite their aggressiveness toward
is especially abundant in the southern half of
other species of ants, Argentine ant colonies
the state. It is typically an outdoor ant
will peacefully coexist with other colonies of
species, but it frequently invades homes.
Argentine ants and will even cooperate with
Argentine ants can be recognized by their
other colonies to form “super colonies.”
small size (workers are about one-twelfth of
Outdoor nest sites often are found in the
an inch long), their uniform brown color, and
soil under things like bricks or boards, rotting
the single upright node found between the
wood, and refuse piles; under bark or other
thorax and abdomen. Unlike fire ant workers,
crevices in stumps or trees; in moist leaf litter
which vary greatly in size, Argentine ant
or organic mulch (this is a real favorite); and
workers all are similar in size. Argentine ant
in bee hives, bird nests, and other similar
workers do not have stings. They can bite,
2locations. Environmental conditions, such as Argentine ants will feed on live and dead
drought, excessive rainfall, or the onset of insects, honeydew produced by insects,
cool weather, may trigger Argentine ants to meats, pet foods, sweets (such as sugar,
move some nests indoors. The presence of syrup, etc.), and many other things. Due to
attractive food sources also may result in the the wide variety of foods they will eat, these
establishment of indoor nests. ants are serious pests in households or other
Indoor nest sites may be located in wall places where food is prepared or stored.
voids, behind insulation, under house siding Although they may not eat large quantities of
or shingles, behind brick veneer, in potted food in homes, they contaminate the food
plants, under carpeting or other flooring, stores, and generally the entire amount of an
and in other protected sites. Nest sites usual- infested product is thrown away.
ly are located in moist areas like bathrooms When they invade homes, these ants also
and kitchens, and indoor nests often are asso- can cause problems simply because of their
ciated with plumbing or structural leaks. sheer numbers, crawling anywhere in the
The Argentine ant is a very aggressive home including shelves, closets, stoves, dish-
species that often displaces native ants. washers, countertops, refrigerators, beds, in
Despite their lack of a sting, Argentine ants clothes, or anywhere else imaginable. These
can even displace imported fire ants. In fact, ants also may spread disease because they
fire ants may be essentially absent in land- tend to crawl over such things as feces, dead
scapes where Argentine ants are well estab- and decaying animals, sewage, and other
lished. Once established, Argentine ants forms of refuse, and then contaminate foods.
become the dominant ant species, and mil- In areas where Argentine ants have be-
lions of ants can be present in a landscape. come well established, it is not likely that
It is not unusual to see large lines of foraging they can be eliminated totally from the land-
workers running up and down trees, on scape. However, there are several things you
fences, on the ground, and throughout can do to help reduce the frequency of indoor
infested landscapes. invasions by Argentine ants. In order to bat-
Because of their small size and hidden tle this ant effectively, you must be proactive,
nests, large populations of Argentine ants using a combination of different methods,
can be present outside without being noticed including sanitation, exclusion, baiting, and
by the homeowner. It is when foraging work- treating with insecticides.
ers enter homes and begin feeding on food
items that they become pests. Because these Odorous House Ants
ants are omnivorous (they eat both animal Odorous house ants (OHAs), known by
and vegetable foods), they will readily feed the scientific name of Tapinoma sessile (Say),
on most types of food they can get to inside are one of the most common species of ants
your home. encountered indoors. These native ants are
When foraging workers locate a suitable quite adaptable and occur throughout the
food source, they lay a chemical trail back to United States. They nest in a wide variety
the nest site, which allows other workers to of habitats, including sandy beaches, pastures
return to the site quickly. This is why indoor and fields, forests, wet areas (such as bogs),
infestations of Argentine ants can appear and houses or other buildings.
overnight. Once they find their way inside, As long as they remain outdoors, OHAs
foraging workers often will branch out, locat- go largely unnoticed by humans and are
ing other food sources. not considered pests. It is when they invade
homes and begin foraging in the sugar bowl
or on other foods that they become a problem.
3Odorous house ant workers are about Inside the home, OHAs feed on a wide
one-tenth of an inch long, are uniformly variety of foods, including meats, vegetables,
brown to blackish-brown, and do not have pet foods, and fruits. They are attracted espe-
an upright node between the thorax and ab- cially to sugar, honey, sweetened cereals, pas-
domen. Like Argentine ants, these ants do not tries, syrup, and other sugary foods. Because
have stings, but they are capable of biting. they like sweets so much, OHAs will take
However, the bite is not very painful because sweet baits readily, especially liquid baits.
the ants are so small. As their name suggests, These baits can help you control OHAs.
odorous house ants have a distinctive odor, In homes, OHAs are most commonly
especially when crushed, and this odor can found in the kitchen/pantry area, but they
help you identify them. can occur anywhere in the house where there
OHAs do not produce large, easily visible is an attractive food source, such as where
nests like those of fire ants. Instead, their pets are fed, where pet food is stored, or
nests are much smaller and may be found in where garbage cans are kept. Because these
the soil or beneath rocks, stones, bricks, logs, ants nest primarily outdoors, indoor infesta-
boards, or other objects on the ground. They tions are likely to be linked to outdoor
also nest under the loose bark of stumps colonies. Foraging ants lay a chemical trail
and logs; in stacks of firewood; in plant from the colony to the food source, and
cavities, insect galls, trash piles, and animal with a little patient effort, these trails often
nests; under mulch in flower beds; under can be identified and followed back to the
shingles or siding; behind ivy or other vines nesting site.
on external walls; behind brick veneer; in
wall voids; and in many other locations. Control of Home-Invading Ants
Indoor nests usually are located in or near a Short-term control of Argentine or odor-
source of moisture. ous house ants can be as simple as locating
This pest has the habit of moving its nest their trail, wiping it away with a damp, soapy
site every few weeks, which can make control cloth, and removing the food source that
more challenging. OHA colonies often consist was attracting the ants or storing it in an ant-
of a main colony, or nest site, and many proof container. Without their scent trail, the
satellite nest sites with queens and broods ants lose their way to the food source, and
of their own. The main colony and satellite are forced to either re-establish the trail or
colonies are interconnected by foraging trails. forage elsewhere.
In most cases where they nest in homes, the If you can follow the trail to a point where
colony also will have other nest sites located the ants are entering your house, apply an
outside. Colony size may range from several appropriately labeled insecticide at this point
hundred to many thousands of individuals. to discourage the ants from re-establishing the
Colonies of OHAs will contain many trail. This is most effective when an outdoor
reproductive queens. colony has only recently established a single
In natural habitats, OHA workers are foraging trail into your home. However, if
noted for their love of honeydew produced there are heavy populations in or around the
by insects such as scale insects, aphids, home, they will likely return eventually, espe-
mealybugs, and plant hoppers. They eat the cially if they have nests already established in
honeydew and tend and protect the insects your home or have readily available routes
that produce it. Additionally, workers regu- into your home.
larly feed on flower nectar and other plant Long-term control of these ants can be
secretions. They also feed on both live and quite challenging, requiring a combination of
dead insects, dead and decaying animals, methods and much persistence and patience.
and a variety of other things.
4Some of the practices that are most useful locally, you can purchase them from mail-
in controlling home-invading ants are order or Internet suppliers.
discussed below. When treating outdoor ant colonies,
choose insecticides that contain one of the
Locate and Treat Nest Sites following active ingredients: bifenthrin, cy-
One step toward eliminating infestations fluthrin, deltamethrin, lambda-cyhalothrin,
of these home-invading ants is to locate and or permethrin.
treat nest sites. Do this by looking for forag-
ing trails and attempting to follow them back Eliminate Attractive Food Sources
to their source. It is especially important to Eliminate attractive food sources by prac-
identify and treat any nest sites located inside. ticing good sanitation and storing food prod-
It usually is impossible to locate all nest sites, ucts in ant-proof containers. If pet food bowls
especially all outdoor sites, but this is an are the cause of the problem, simply limit the
important first step. When you locate a nest amount of time you leave the food bowls out.
site, treat it with an appropriately labeled Remove the food at other times, rather than
residual insecticide. If you think ants are giving the pet—and, consequently, the ants—
nesting indoors but you cannot locate or free access to the food.
access the nest sites, use baits as described You may need to make a thorough search
in a following section. of your home to identify food sources and
When choosing an insecticide, read the label either remove them or store them in ant-proof
carefully before you purchase the product, and containers. Storing foods in ant-proof contain-
be sure that it is labeled for the particular use ers, or in the refrigerator or freezer, is a key
that you have in mind. If you need to treat ant management tool, especially in homes
inside your home, be sure that the insect- that suffer chronic infestations. This practice
icide is specifically labeled for indoor use. also helps prevent infestations of other
Note that two products with the same active stored-food pests.
ingredient may have very different labels;
one may be formulated specifically for in- Seal Entry Points
door use while another may be restricted to Although it is usually impossible to locate
outdoor use. and seal all potential entry points, sealing
Examples of insecticides that can be used points where you have observed trails enter-
to treat indoor infestations of ants include ing your house can help divert foragers to
aerosol sprays containing active ingredients other outside food sources. When sealing
such as prallethrin + tralomethrin, prallethrin cracks and entryways for ant control, keep
+ esfenvalerate, or pyrethrins + PBO + in mind that it is important to retain adequate
permethrin; and ready-to-use trigger pump ventilation of your home for health and
sprays containing active ingredients such as safety reasons.
bifenthrin, cyfluthrin, permethrin, delta-
methrin, or tralomethrin. Prune Trees and Shrubs
Treat nest sites located inside walls or Limbs of trees or shrubs that touch the
other voids with an insecticide dust contain- exterior of your house provide convenient
ing the active ingredient deltamethrin, or with travel ways for foraging ants to enter.
dusts containing silica or diatomaceous earth. Keeping limbs and branches pruned away
Apply dusts using a commercially available from your house can aid greatly in ant con-
bulb duster that allows you to “inject” dusts trol. Also, remove any ivy or other vines
through small holes drilled into the target growing on the building because vines can
void. If you cannot find dust applicators provide nesting sites and lead ants inside.
5Control Honeydew-Producing Insects on Baits are intended to work slowly so that
Landscape Plants they will be carried back to the nest site and
Because these ants thrive on honeydew spread throughout the nest to both adult and
produced by pests such as aphids, scales, and immature ants, eventually eliminating the
whiteflies, controlling these pests on land- entire nest. Do not apply insecticide sprays in
scape plants can aid in ant control. Likewise, areas where you are using baits because the
because ants tend and protect these honey- sprays tend to repel ants and prevent them
dew producers, controlling ants can help from taking the bait. Likewise, do not disturb
control the plant pests. the foraging trails to the bait; just keep check-
ing and replenishing the bait as needed.
Avoid Excessive Mulch and Leaf Litter Examples of baits that can be useful
Both Argentine ants and OHAs readily against home-invading ants include liquid
nest in the moist, protected environment pro- sweet baits, gel baits, and bait stations. These
vided by organic mulch or leaf litter. Help may contain active ingredients such as ortho-
control these ants by keeping mulch and boric acid, disodium octaborate tetrahydrate,
leaves away from the foundation wall of your fipronil, abamectin, or arsenic trioxide. Finely
house and avoiding the use of excessive ground granular baits containing ingredients
amounts of mulch. Where feasible, use rock, such as orthoboric acid or abamectin also
pea gravel, or some other non-organic mulch may be useful in some situations. When
in the area immediately adjacent to the foun- using baits, you must put the baits in all loca-
dation. Maintaining a mulch- and leaf-free tions where ants are foraging. If you have
area of even 3 to 4 feet around the immediate seen ants in the kitchen, den, and a bathroom,
perimeter of your house can aid greatly in ant bait all three locations. You also may want to
control. This also helps eliminate entry points place appropriate baits outside where you
for termites. have observed foraging trails. However, out-
door infestations often are difficult to control
Use Appropriate Baits Properly with baits simply because of the large num-
Against Argentine ants and OHAs, baits bers of ants involved. This is especially true
are most useful for eliminating indoor nest with Argentine ants.
sites that cannot be located and treated direct-
ly. Note, however, that baits designed for con- Apply Perimeter Insecticide Treatments
trol of fire ants usually are not very effective If heavy outdoor populations are causing
against Argentine ants or OHAs, and neither continuous re-invasion of your home, try
of these ants are as easy to control with baits applying treatments of residual insecticide
as are fire ants. to a 3- to 10-foot-wide band around the
Baits that are designed for use against perimeter of your house. These perimeter
these ants can be useful, but they take time to treatments can help control any nests located
work, usually several weeks, and you must in the area and control or discourage foraging
keep the bait fresh and replenish it regularly. workers from nests located farther away from
The objective is to place baits along foraging your home.
trails where the ants will find them readily Examples of active ingredients used in
and to keep providing bait as long as the ants insecticides labeled for such perimeter treat-
are foraging on it. Sometimes the ants will ments include: bifenthrin, carbaryl, cyfluthrin,
detect the insecticide in a bait and quit feed- deltamethrin, lambda-cyhalothrin, and per-
ing on it. When this occurs and ants are still methrin. Read and follow the label directions
present in your house, change baits and bait- carefully. Some labels allow treatment of a
ing locations in an effort to get ants to resume portion of the outer wall of the home and
taking the bait. around doorways and windows, while others
6do not. Also, the width of the treated band can take time and several repeat visits to
varies from product to product. obtain results. Once the ants are under con-
trol, continued service will be necessary to
Hire a Professional Pest Control Company maintain control.
Obviously, this is an alternative to the do- One useful treatment that can be applied
it-yourself approach. Professional technicians only by licensed professionals is a perimeter
will have access to useful treatments that are treatment of fipronil (Termidor is the brand
not readily available to the general public. name) around the outside of the building.
They also will be better equipped to drill and This involves applying a spray 1 foot up the
treat wall voids if such treatments are neces- side of the building and 1 foot out from the
sary. Most companies have experienced tech- base of the building, as well as to entry points
nicians who know and understand how to and trails. This treatment has proven to be
deal with ant problems. especially helpful when combined with the
However, don’t expect an overnight other methods previously discussed.
solution. The technician still will have to
use the methods discussed above, and it
7The information given here is for educational purposes only. References to commercial products, trade
names, or suppliers are made with the understanding that no endorsement is implied and that no dis-
crimination against other products or suppliers is intended.
By Blake Layton, PhD, Extension Entomologist, and Joe MacGown, Scientific Illustrator, Biochemistry,
Molecular Biology, Entomology, and Plant Pathology.
Discrimination based upon race, color, religion, sex, national origin, age, disability, or veteran’s status is
a violation of federal and state law and MSU policy and will not be tolerated. Discrimination based
upon sexual orientation or group affiliation is a violation of MSU policy and will not be tolerated.
Publication 2407
Extension Service of Mississippi State University, cooperating with U.S. Department of Agriculture.
Published in furtherance of Acts of Congress, May 8 and June 30, 1914. GARY B. JACKSON, Director
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