Integrated Pest Management Manual
Ants are among the most successful insects. Experts estimate that there could be 20,000 or more species of ants in the world. They have evolved to fill a variety of different ecological niches as predators, herbivores, leaf-cutters, seed-harvesters, aphid- tenders, and fungus-growers. They are found in deserts and rainforests, mountains and valleys, from the Arctic Circle to the tip of South America. They are interesting organisms that should be studied to better understand their unique behaviors and their roles in the earth's ecosystems.
They can also be pests, however. Fire ants and others may sting or bite people and animals. Pharaoh ants get into wounds and dressings in hospitals. House-infesting ants can become pests by their presence in kitchens and living areas. Carpenter ants tunnel into structural wood. Mound-building ants mar the appearance of lawns and landscaped areas. Sometimes ants must be managed to suppress a pest problem.IDENTIFICATION AND BIOLOGY OF ANTS
Only a comparatively small proportion of ant species are damaging and require control. For National Park Service personnel, the ants most often of concern will be species in three groups: fire ants, carpenter ants, and house-infesting nuisance ants. The first two are discussed in separate Integrated Pest Management modules. This module addresses the third group, house-infesting ants--those ants that most commonly invade structures looking for food, water, or nesting sites.
A detailed description of every pest ant is beyond the scope of this module. Well over a dozen are considered common pests of structures, and many others are occasional pests. The species most likely encountered will depend on geographic location and surrounding habitat. Detailed information on identification, biology, and management of specific pest ants should be obtained from the local Cooperative Extension Service, your regional National Park Service Integrated Pest Management coordinator, or from the References listed at the end of this module. A table that lists key features used to identify major pest species of ants follows.
|Species||Worker size||Color||Thorax shape||No. of nodes||Other id characteristics||Treatment||Bait|
|Pavement ant||3/16"||dark brown||uneven||two||Grooves on head and thorax. Stinger at tip of abdomen.||
|Thief ant||1/32"||yellow||uneven||two||Stinger at tip of abdomen||barrier-poor||sweet or protein|
|Crazy ant||1/8"||dark brown||uneven||one||Very long legs. First antennal segment twice as long as head.||
|sweet or protein|
|Field ant||3/18"||brown to very dark brown||uneven||one||none||barrier-excellent||sweet|
|Pharoh ant||1/16"||yellow with red abdomen||uneven||two||none||barrier-poor||sweet or protein|
|Argentine ant||1/8"||brown; sometimes light brown||uneven||one||sparse body hairs; no hairs on thorax||barrier-poor||sweet|
The Ant Colony and Life Cycle
Ants belong to the insect order Hymenoptera, which also includes the wasps and bees. Ants are distinguished from many of their nearest relatives by two characteristics: a narrow "waist" (the slender free-moving portion of the abdomen called a (pedicel) and elbowed antennae.
Ants also differ from most other insects in that they are social, similar to termites and certain bees and wasps. This means that ants live in large cooperative groups called colonies. Two or more generations overlap in the colony; adults take care of the young and are divided into castes, specialized groups that take care of certain tasks. Ants have reproductive castes, the queens and males, and nonreproductive castes, the workers.
Queens. A queen is generally the largest individual in the colony. She has wings until after her mating flight, when she removes them. The primary function of the queen is reproduction, but after establishing a new nest she may also care for and feed the first brood of workers. Once she has produced her first brood, she becomes an "egg-laying machine," cleaned and fed by her offspring. She may live for many years until replaced by a daughter queen. Some ant species have more than one queen in the nest.
Males. Male ants are generally winged and usually keep their wings until death. Apparently, the male ant's only function is to mate with the queen. Once he does, he dies, generally within two weeks. Males are produced in old, mature colonies.
Workers. The workers are sterile, wingless females who build and repair the nest, care for the brood, defend the nest, and feed both immature and adult ants, including the queen. There may be workers and soldiers of different sizes that specialize in certain tasks.
Ants develop through a complete life cycle of egg, larva, pupa, and adult. The egg is tiny, almost microscopic in size. The larva is legless and grub-like, very soft and whitish in color. It is also helpless and depends totally on workers for food and care. The pupa looks somewhat like the adult but is soft, unpigmented, and cannot move around. Some are enclosed in a cocoon, some are not. A newly-emerged adult requires several days for its body to harden and darken.
New Colony Formation
Once a colony of ants matures, it can establish new colonies through various methods, depending on the species. The two most common are budding and swarming. The appropriate management strategy depends on how a colony spreads, so it is essential to correctly identify the ant species before deciding how to manage it.
Budding. Budding is the breakaway of a group of ants from a mature colony to form a new colony. The group usually consists of one or more queens and some workers carrying larvae. Budding is common with species of ants that have multiple queens, such as Pharaoh ants and Argentine ants. Residual insecticides should not be used for ants that undergo budding because they can stimulate this process.
Swarming. Most ants establish new colonies through swarming. Every now and then, particularly in spring or early summer, mature ant colonies generate large numbers of winged forms. These are the young queens and males, going off to mate. An inseminated queen then rids herself of her wings and attempts to start a new nest in a cavity, under a stone or a piece of bark, or by excavating a hole in the ground. She rears her first brood alone, feeding them with salivary secretions and infertile eggs. If successful, the first brood opens up the nest and brings in food for themselves, the queen, and subsequent broods, and the colony grows. However, the percentage of queens that successfully begin new colonies is thought to be very small.
The Difference Between Winged Ants and Winged Termites
Although ants and termites are very different, they are often confused. They are alike in that they live in colonies and periodically swarm. Swarming forms of both are dark and winged. But worker termites are whitish and never seen running freely about as do ants. Instead, termites remain protected in their nests and galleries in wood and soil.
Winged adult ants can be told from winged termites by the following differences. Winged ants have a narrow waist, front wings that are larger than the rear, and elbowed antennae. Winged termites have a fat waist, equally sized wings, and straight, beaded antennae.
Most outdoor ants increase in population and activity from spring into summer months and then decline from fall into early winter as the temperature drops and the ants' natural food supplies dwindle. Other ants, such as the Argentine ant, may increase in numbers in the fall as various colonies aggregate together to overwinter. Some ants, such as the Pharaoh ant, which may live entirely indoors, exhibit little seasonality.
Knowing the food habits of the particular ant species is important in ant management because it may enable the location and elimination of the food that is attracting the ants to the site, it can help to locate foraging trails to track the ants back to their nest, and it can help to choose an effective bait.
Ants feed on many different types of food. Some species will feed on practically anything; others may limit their food to a narrow range. Ants infesting structures are typically feeding on "people food," both food in storage (sugar, cakes, cookies, breakfast cereals, etc.) and food from spills and garbage. But they may also be preying on other insects or scavenging on dead insects in windows or lights.
Food preferences are often seasonal. When the queen is actively laying eggs, worker ants typically gather protein- based foods for the queen. At other times they may ignore protein foods completely and restrict their foraging to sugars and greases.
Many ants obtain sugar by feeding on honeydew, a sweet substance secreted by aphids and other plant-sucking insects. They often defend these insects from predators and tend them as if they were their personal food supply. Indoor infestations of ants are occasionally traced to large populations of aphids on outdoor foundation plants or indoor houseplants.
The six most common ant species that infest buildings are the pavement ant, the thief ant, the crazy ant, the field ant, the Pharaoh ant, and the Argentine ant.
Pavement Ant Identification and Biology
Pavement ants (Tetramorium caespitum) were introduced to the United States from Europe and occur throughout the eastern United States. They are an important pest in the Midwest and New England. These are small ants, about 3/16" long, and are dark brown in color. They build nests along sidewalks, building foundations, and under stones, boards, bricks, and mulch or leaf piles. These ants readily make trails to and from food sources and often forage along the edge of carpeting or baseboards. They are also common around the base of toilets. They often nest in protected areas so the nests may be hard to locate, but this is essential to manage infestations of this species. There can be several thousand in a colony.
Pavement ants feed on a wide variety of foods including other insects, greasy foods, and plants. While they are often found in damp areas, lack of moisture does not limit their development, so solving moisture problems alone will not affect these ants. Vegetation-free borders should be installed around buildings, and any cracks in building foundations should be sealed. Any loose material under that could provide nesting habitats and should be raised off the ground.
Thief Ant Identification and Biology
The native thief ant (Solenopsis molesta) is found throughout the United States, but primarily in the eastern and central states. A very small ant, thief ants are easily confused with the Pharaoh ant. The best way to tell them apart is to look at the club on the end of the antenna with a magnifying glass and count the number of segments; thief ants have two segments, while Pharaoh ants have three. Thief ants are named for their habit of stealing food from the nests of other ants. They nest outside under debris, rocks, or logs; indoors they nest in wall voids and behind baseboards. They are very small and can easily enter packaged foods, so food should be enclosed in tightly-sealed containers. Locating thief ants' nests can be difficult and time-consuming because their small size can make it difficult to follow the trail. Thief ants feed on both protein and sweets and will tend aphids, mealybugs, and scales to obtain the honeydew they excrete.
All cracks in walls should be sealed to keep these ants from entering buildings. Patience is essential in managing the ants because the nest can be so hard to locate. Baits do not seem to be effective for thief ants since they tend not to eat enough bait to bring sufficient quantities back to the nest for it to work.
Crazy Ant Identification and Biology
Crazy ants (Paratrechina longicornis) were introduced to the United States from India. Their distribution is limited to the Gulf coast from Florida to Texas. They are easily identified by their long legs and their habit of erratically moving from place to place (hence the name "crazy"). Crazy ant trails are not readily obvious because of this erratic movement. The easiest way to find the nest is to look for workers carrying pieces of food or workers with swollen abdomens. These ants are carrying food back to the nest. By observing their movement, it should be possible to find the nest. Crazy ants are highly adaptable and will nest in a variety of locations, from very dry to moist. They will nest under objects, in rotten wood or trash, in tree cavities, as well as in debris left standing in buildings for long periods of time.
These ants feed on a variety of foods including grease, sweets, and other insects. In some areas they are considered a biological control agent for houseflies. They also tend aphids and scales to feed on their honeydew. While crazy ants need moisture, elimination of water by itself will not get rid of these ants since they can survive under a wide range of conditions. Elimination of food sources and nest sites are equally important in the management of this ant.
Crazy ants do not respond well to baits, so they cannot be relied upon for management of this ant. Surrounding buildings with vegetation-free barriers such as stone or brick (but not wood mulch) will keep ants from entering buildings to nest.
Field Ant Identification and Biology
Field ants (Formica spp.) are found throughout the United States but primarily in the Midwest and North. They are large (3/8" long) and dark brown to black. They are often confused with the carpenter ant, but can be distinguished by an uneven thorax (see ant identification chart at the end of this module). Field ants feed on other insects as well as insect honeydew. They cause concern because they usually nest near structures and are often mistaken for carpenter ants. Nests are often made in grassy areas and can be difficult to see because they are low to the ground. Field ants will also nest in leaf litter or mulch that is more than two inches thick, and can live under stones, firewood, or other debris that might be found in a lawn area. If pesticide drenches of mounds are used to manage this insect it should be remembered that they will be slow to act because it often takes foraging ants days to return to the nest.
Pharaoh Ant Identification and Biology
Pharaoh ants, (Monomorium pharaonis), are small yellow ants about 1/16" long. They are easily confused with thief ants, also a small yellow ant. To distinguish the two, it is necessary to look at the antennae. Pharaoh ants have twelve segments with a three-segmented club on the end, while thief ants have ten segments with a two-segmented club. Pharoah ants are native to tropical Africa but are now distributed throughout the world. They are usually associated with heated buildings since they cannot survive outside year round in the majority of the United States. These ants will nest in any dark void in a structure as well as in folded bags or newspapers. In the subtropical United States they will nest outside in leaf litter, piles of bricks, potted plants, or under roof shingles.
Pharaoh ant colonies can become quite large, often containing as many as 300,000 workers with several queens. New colonies are formed by budding, when some of the workers, brood, and a few queens move to a new location. In warm areas where they can survive outdoors they will move from building to building.
Pharaoh ant management is more dependant on locating areas of ant activity than eliminating the colony, since they are so large and can spread so easily. Place jelly baits on 1" squares of paper or tape and place in damp, dark areas. These ants move along electrical wires, so an inspection should include areas where wires enter walls or appliances, as well as behind switchplates and outlets. Pharoah ants will also nest in and around appliances such as refrigerators or stoves that have food or water around them. A useful tool for the management of this ant is to make a map of the site and mark locations where ants and their colonies are found. This will help to identify new areas of activity over time.
Sanitation is essential for Pharaoh ant management, since elimination of food sources will make them more receptive to insecticide baits. Residual insecticides should not be used for Pharaoh ant management. They can repel ants, forcing more colonies to form through budding while killing only a small number of ants. During the first two to four weeks of the program, place baits containing an insect growth regulator and a food attractant inside a soda straw throughout the area of infestation. These should be located along edges and in corners where ants are most likely to encounter them. Placing baits inside straws will keep them fresh and away from people and domestic animals. Replace these with boric acid/food attractant baits. One food bait is three parts honey: two parts peanut butter: one part mint apple jelly : one part egg yolk baby food. Commercial baits are also available. Exterior treatments may be necessary in subtropical areas of the United States or during the warmer months in northern areas. Remember that both insect growth regulators and boric acid are EPA- registered pesticides, so your regional National Park Service Integrated Pest Management coordinator should be consulted before using these materials.
Argentine Ant Identification and Biology
Argentine ants, (Iridomyrmex humilis), are an imported species common throughout the southeast and southern California. These ants will nest in soil and mulch, as well as under stones, logs, and debris. They are often found in tree holes, bird nests, leaf litter, and bee hives. These ants form large colonies; workers from different colonies do not fight and will often join together to form larger colonies. This means that areas from which colonies are eliminated can quickly be repopulated. These large colonies will often split by budding during the warmer months. Although Argentine ants form winged reproductives, they do not swarm. They feed on a variety of foods but seem to prefer sweets and will feed on aphid honeydew. They will even feed on fruit crops and are considered an agricultural pest in some areas.
Argentine ant trails are easy to locate along sidewalks, foundations, and along the edges of buildings. If grass grows to the edge of the building it should be pulled back during an inspection. These ants will also move into buildings by climbing up trees onto wires entering buildings, so any place where branches touch buildings should be inspected as well. As with so many other ants, use of a vegetation-free border and correction of moisture problems will help in management of Argentine ants. Insecticide baits are useful for managing this ant.
MONITORING AND THRESHOLDS
Identification of the species will help to determine where the nest might be located, what the ants might be feeding on, and the best tactics for control. All parts of the building and the surrounding area should be inspected for ant activity as well as food and water sites. People that work in the building might have seen the ants also. Some species are most active in the evening. For these, a daytime inspection might discover little, while significant ant activity might be observed at midnight.
Some infestations may require an intensive survey program using nontoxic baits to determine likely nesting sites. Good baits are jelly, honey, peanut butter, bacon grease, or raw liver. The baits (or a combination of baits) should be placed on small pieces of cardboard, aluminum foil, masking tape, or plastic pill bottle lids throughout the building and periodically checked for feeding ants. Active sites should be noted on a survey diagram. Baits that haven't had any feeding activity in 24 hours should be moved. Over a period of days the survey diagram will pinpoint areas of activity. In addition, trails of ants feeding on the bait can sometimes be followed back to the nest site.
There is no single threshold level for house-infesting ants. Threshold levels need to be set separately for each site. For example, a single ant in a first-aid station may be one too many. In an eating area, control actions might be initiated if there were more than a half-dozen ants in a day, while most people's tolerance for ants in a rustic and open recreation room would likely be much higher.
NON-CHEMICAL CONTROL OF ANTS
The most effective ant control results from the destruction of the queens and the nest itself. If the nest is found by tracking workers, or through a survey, eliminating that nest is fairly simple, particularly if it is located, as it often is, outdoors, or in the soil beneath a cracked floor. It is simply a matter of mechanically destroying the nest.
But effective ant management is rarely that simple. Sometimes you can't find the nest. Often there are multiple nests. (One species, the Pharaoh ant, can have hundreds of small nests within a single room.) There may be a constant pressure from ant colonies invading from surrounding areas. In most cases, long-term management of pest ants means integrating improved sanitation, structural repairs, and habitat modification along with one or more direct control tactics such as insecticide baits, crack and crevice treatments, and direct physical controls.
Successful ant management usually requires a combination of management tactics, ranging from caulking to cleanup, improved sanitation to habitat modification, as well as targeted and limited insecticide treatment.
The keys to success in ant management are, first, vigorous inspection to determine the nature and extent of the infestation, and, if at all possible, the location of the nest. Second, meticulous sanitation to eliminate readily available food and water. Third, the choice of the right combination of tools to eliminate the problem. The listing for each ant species provides more information on management strategies relevant to that ant.
Like all pests, ants need food, water, and shelter to survive. By limiting these three essentials, you make it more difficult for ants to live in the infested area. Simply by improving sanitation you can often suppress existing populations and discourage new invasions.
Ants can enter many types of food packaging, particularly once the package has been opened. (They have even been found inside glass jars after traveling around the threads of a screw-on lid!) Cereals, sugar, and other bulk food should be stored in plastic containers with snap-on lids, in glass jars with rubber seals, or in a refrigerator.
Food spills also feed ants. As with cockroaches, enthusiastic cleaning helps to minimize ants. Frequent vacuuming, sweeping, or mopping of floors and washing of counter and table tops eliminates much of the food ants may be foraging on. Trash should be stored away from infested areas and monitored for spills.
Ants can get their water from many sources inside a structure: condensation on pipes and air conditioners, leaky plumbing, aquariums, pet dishes, houseplant containers, floor drains, etc., and limiting these is rarely practical.
Ants can enter and move through a structure through innumerable tiny cracks and openings. Yet caulking and otherwise sealing cracks and crevices being used by ants can often have great effect in suppressing the population. Many easy-to-use and effective silicon sealers and expandable caulk products have been recently developed, including some designed specifically for pest management. Repairing torn screens and installing doorsweeps can also prevent ants from easily entering a structure. Non-vegetation barriers such as stones or brick walkways next to a building can be helpful in helping to keep ants out of structures as well.
Trim the branches of trees located close to structures so the branches do not act as runways from nest sites to roof or siding. Alter landscaping to minimize the number of aphids and other honeydew-producing insects that attract ants. Firewood kept indoors should be moved outdoors or regularly inspected for ants. Don't stack wood next to structures and move trash, since ants often nest under objects. Moisture accumulation in buildings can also result in ant infestations.
Direct Physical Control
Ants can be discouraged from foraging in certain limited sites with sticky barriers. For example, commercially available sticky repellents or petroleum jelly can be applied in a narrow band around table legs to prevent ants from walking up to the tabletop. Double-sided tape can also be used.
Large numbers of worker ants can be mopped or sponged up with soapy water. Water, especially boiling water, has also been used to flood ant nests. Some ground-ant nests have been destroyed by digging them up and destroying the nest structure.
CHEMICAL CONTROL OF ANTS
Many people, on discovering ants, simply spray insecticide wherever they have seen ants. This is a poor strategy, usually doomed to failure. Applying undirected, general insecticide sprays indoors is unsatisfactory because the sprays only "harvest" a small portion of the workers and have little effect on the colony, the ultimate source of the problem. A further problem is that some species are apparently triggered into "budding" new colonies when they contact insecticide near their nests and foraging sites.
The chemical tools available for ant control have changed in the past few years with the addition of insect growth regulators, new baits, and commercial bait stations, and new tools can be expected in the future. Even so, insecticides are only one of the tools available for control of ants, and not always the best or most important. Ant biology should be considered when deciding whether or not to use insecticides. For example, insecticides are often not effective against mound ants because it often takes foraging ants several days to return to the nests. Consult your regional National Park Service Integrated Pest Management coordinator for information on using pesticides as part of an ant management program.
Ant baits. The best baits for ants are those whose toxicant kills ants slowly. In this way, worker ants live long enough to take the baits back to the nest and feed it to the colony and queen. A number of baits are now available. Some are prepackaged in child-resistant bait stations. Some are gels or pastes designed to be placed in small pea-shaped amounts throughout an area. Some products (such as boric acid) are designed to be mixed with a food. Bait products typically will work against certain species of ants but not against others, so it is important to check the label to make sure the ant you wish to control is listed.
Insect growth regulators (IGRs). These are available in bait form for some ant species. Insect growth regulators inhibit normal development of insects. They are slow-acting because they stop the next generation from developing rather than killing the current generation. A recent study comparing the insect growth regulator fenoxycarb to a commercial bait found that the growth regulator was more effective than the bait in eliminating Pharaoh ants. This is most likely because the bait kills ants too quickly to be effectively distributed throughout the colony (Williams and Vail 1994). Crazy ants do not seem to respond well to bait, and baits may be slow-acting against field ants since they often stay away from the nest for several days.
Liquid and aerosol insecticides. Nearly all of the insecticides labeled for use against cockroaches are also labeled for use against ants. These insecticides are most effective when used to treat actual nest sites. Insecticides are less effective, but still may provide acceptable results when used to treat inside cracks and crevices used by ants in and around infested sites. They are least effective, as well as offering the highest potential of human exposure, when they are simply applied to sites where activity has been observed.
Drenches. For certain ground-nesting ants that dig deep nests outdoors, a soil drench or mound drench can be effective where other treatments are not. As its name implies, a soil drench consists of applying enough insecticide dilution directly to a mound or nest so that the entire nest is drenched.
Dusts. Dusts may also be used on occasion for ant control if they are used lightly or directed into nests. In large amounts, dusts tend to repel ants. But they have the advantage of floating back through wall voids to reach nests that may not be accessible with other formulations.
Granules. Granules are rarely used in household ant control. They may be useful, however, when a lawn or field is heavily infested with many colonies of a shallow, ground- nesting species of ant.
1. Williams, D.F., and K.M. Vail. 1994. Control of a natural infestation of the Pharoah ant (Hymenoptera: Formicidae) with a corn grit bait of fenoxycarb. Jrnl. of Econ. Entomol. 87(1): 108-115.
Sources of Additional Information
1. Bennett, G. W., Owens, J. M., and R. M. Corrigan. 1988. Truman's Scientific Guide to Pest Control Operations. (4th Edition). Edgell Communications, Duluth MN.
2. Ebeling. W. 1975. Urban Entomology. Univ. Calif., Div. Ag. Sci.
3. Hedges, S. 1991. Field Guide for the Management of Structure-Infesting Ants. GIE Inc. (PCT), Cleveland, OH.
4. Mallis, A. 1990. Handbook of Pest Control (7th ed.). Franzak & Foster Co., Cleveland, OH.
5. Olkowski, W., Daar, S., and H. Olkowski. 1991. Common- Sense Pest Control. The Taunton Press, Newtown, CT.
6. Smith, M.R. 1965. House-infesting ants on the Eastern United States. Tech. Bull. 1326. Agricultural Research Service, U.S. Department of Agriculture, Washington, D.C.