[Ant Control] Tackling ANT Infestations

A basic tenant of sound ant pest management, there is no shortcut around a thorough inspection.

April 14, 2004

According to pest management professionals from  around the country, ants are still the No. 1 reported nuisance pest in the United States. When talking to pest management professionals around the country I’ve learned that ant treatments are still a bread-and-butter service for many companies. Controlling ants in and around structures is sometimes portrayed as difficult and complex but it doesn’t always have to be.

Basically you have to follow four steps to implement ant control: 1) Identify the ant species in question; 2) Perform a thorough inspection, searching for ants, damage, past ant activity, etc.; 3) Determine the location of the ant colony; and 4) Attack the colony directly (either by direct spray or by insecticide translocation with a bait). Follow these steps and you are on the road to providing your client with a sound pest management strategy. There are, of course, a number of pest species in the United States each with specific feeding, foraging and reproductive behaviors. Getting to know the specifics of these particular ants in your area of the country is paramount.

This story will focus on inspection techniques and discuss some tips for conducting inspections for the five major pest ant species in the United States. Of course, these methods may be modified to suit your needs when you are certain of the ant species you are trying to control.

In most cases when you receive a nuisance call the homeowner will be able to tell you little more than they are "little red ants" or "big black ants." Did I already mention that the first step is to identify which ant species you are working with? Well, having no fear of sounding like a broken record, make certain that you properly identify the species of ant you are working against.

What is the best way to ensure a proper ID? There are plenty of good ant identification resources out there; don’t be afraid to use them and train your technicians that do ant inspections/treatments to use them as well. Technicians should be familiar with the key pest species in the area where your business operates. Training technicians to identify worker ants, damage, mound structure, etc., is impressive and helps build client confidence.

I also recommend that you confirm the species in question using a key or other reliable identification source if there is any question whatsoever as to what you are dealing with. If ants are a major part of your operation, and they should be, technicians also should be trained as much as possible in basic biology and behavior of the primary pest ant species in your area.

Since baiting for many species of ants is a popular treatment technique, learning how each ant species forages, feeds, nests and reproduces is important. This knowledge helps you attack a particular infestation but the customer satisfaction and trust that is gained when a technician shows that they know more about a pest than just how to kill it is also a highly valued trait in today’s best trained pest management professionals. State and county extension agents can steer you in the right direction of good ant identification materials and there are also a number of publications, guides and taxonomic keys available directly from The PCT Media Group (www.pctonline.com/store).

Thank goodness only about a few dozen or so of the 700 ant species that are found in the United States have reached pest status by regularly infesting homes and other buildings. Likely you will not have to deal with all of these species within a given geographical area. Usually the top five we take into consideration in the United States are as follows: Argentine ants, fire ants (complex), carpenter ants (complex), Pharaoh ants and pavement ants. Each of these species or species complex has a unique set of characteristics and behaviors. Following are some tips for conducting inspections when targeting each of these pest species.

ARGENTINE ANTS. Argentine ants are common in many parts of the United States and are especially problematic in California. They are capable of building nests in almost any situation including soil, firewood piles, mulch, tree holes, and even under concrete and blacktop drives and sidewalks. Their colonies can consist of thousands upon thousands of workers and multiple queens. Additionally, this species is capable of "budding." Budding results when a queen and some workers from the main colony split off to form their own colony. This is one reason that residual insecticide treatments must be used with caution as they can cause budding if workers and a mobile queen are trapped/prevented from returning to the main colony. Inspect for Argentine ants by searching for their large trails.

Where Argentines are present they are readily found along edges of a structure or edges of the landscape (e.g., walkways, branches, shrub beds, etc.). As with other ant species, you can turn over any object lying on the ground to search for nests in the outdoor environment. Additionally, nests can be found underneath landscaped lawns. Following trailing ants can be difficult in this case but necessary if the nest is to be located. If there are mulch beds around the structure these too should be inspected for ant colonies or foraging ants.

Argentine ants can enter the home through any entranceway from the ground but wires and cables entering the house should also be inspected for trailing ants. Trees or brush that contact the house is also another potential entry point where trailing ants can gain access to the structure. Once inside the structure foraging/trailing ants tend to follow edges of walls or furniture. As with all indoor ant inspections you may have to pull the carpet back from the floor and wall to find these foragers. Be sure to have the tools necessary to do this and to make positively sure that the carpet is returned back to its original state when you are finished with the inspection. Argentine ant trails found inside the structure should be followed. It is likely that the ants are coming from the outside, however this species will sometimes colonize a wall void.

FIRE ANTS. Due to their aggressive behavior and sting, fire ants can be a problem both in and out of the structure because of the serious health risk they pose. In fire ant country, mounds can be found anywhere around the structure and therefore a thorough inspection of the front and back yard area is important. Mounds are generally built in the open sunny area, e.g. the back yard, however as we have dealt with this pest over the years we’ve learned that they can be adaptive in where they construct nests. Sprinkler heads, junction boxes, under log piles, or debris wood, around the base of swimming pools, at the base of trees or fence posts, underneath the concrete patio slab or blacktop driveway, etc. — the list is endless. Suffice it to say that when inspecting a residential home a thorough outdoor inspection cannot be stressed enough.

Often, fire ants will not enter the structure unless extreme drought conditions occur in which case they can enter the house from almost any opening. In slab foundations, fire ant nests can be found in wall voids inside the structure. Ants gain entrance to the structure from the ground and can usually successfully follow plumbing lines to gain access. For this reason, water traps, showers (bathrooms in general), and hot water heaters are all key areas to inspect for fire ant activity. As with all of the ant species mentioned here, you may attempt to follow ants as they trail to learn more about their entry points which will lead to the colony or provide information for where baits may best be placed.

Fire ant trails are often quite large, comprised of more than one row of workers. Trails may be observed around the edges of structures, in the yard or grassy areas, or on walls even above the first story. A common entrance point for fire ants from the exterior to the interior is the expansion joint/slab area. Once inside, fire ants will trail along room edges usually under the carpet. You should plan to lift up carpet edges during inspections to find trailing ants.

CARPENTER ANTS. Carpenter ants are best known for hollowing out moist wood to be used as a nesting site. Probably the single most important factor to key in on when performing carpenter ant inspections is locating high moisture areas within the structure and pinpointing your inspections to these areas. A useful tool for determining high levels of moisture is one of the many moisture meters that are available on the market. You may already have this tool if you also conduct termite inspections.

Although your client may tell you otherwise, carpenter ants do not eat wood. They form their nests by chewing off and removing small bits of the usually moist wood from an area in which they build their nests. These bits of wood are usually placed right outside of the nest, sometimes in distinct piles. This is one telltale sign of a carpenter ant infestation. Carpenter ants feed on a wide variety of foods but their mainstays include dead insects (proteins) and honeydew from the many insects (such as aphids) that produce this carbohydrate-rich substance.

In addition to the traditional hollowed out tree or wood structure, carpenter ants are also capable of nesting in any hollow void, usually if it provides sufficient moisture. Within the structure this can result in a number of different places that will need to be inspected. Wall voids, hollow wooden doors or any hollow structure for that matter, under insulation in crawlspaces, and, of course, firewood piles and any debris wood that is in contact with the ground are just a few spots that carpenter ants may set up shop. Remember that these sort of places, coupled with higher than surrounding moisture gradients (more than 20 to 25 percent), are likely spots for an infestation. It is a good idea to discuss the history of water leaks within the structure with clients, as these are good starting points for an inspection.

Carpenter ants are capable of forming satellite colonies, comprised of workers and immature larvae/pupae. The main colony may be outside of a structure whereby one or more satellite colonies can be found within the structure. Additionally, one carpenter ant colony may have a main nesting site on one property with one or more satellite colonies located on adjacent properties in urban settings where houses are not separated by a great deal of real estate. These are a few characteristics that make controlling a carpenter ant infestation tricky. Once a colony is located you must still inspect other areas like those mentioned previously to ensure that there are not other satellite colonies that are in or near the structure.

PHARAOH ANTS. Pharaoh ants are found all over the United States. They are most common in the South but can be found as a major pest in institutions, such as hospitals and retirement homes, in the northern parts of the country as well. This particular species often tops the list as one of the most difficult species to control and has left many a pest management professional frustrated. Many factors contribute to this.

Pharaoh ants do not have structured nests as do other pest species. Any dark, protected and moist spot can provide them with a nesting site. That means that they can hide almost anywhere within the structure. Colonies can be quite large, in the hundreds of thousands, with multiple queens and the ability to bud or branch out. All that is needed to start a new colony is a few workers and brood and a dark, moist nesting site. This is, in fact, how many Pharaoh ant infestations are started, especially in the northern regions of the U.S., where this species does not overwinter outdoors. As a result, inspecting for these ants can take some time because you may have to look everywhere.

In residential areas, focus your inspection on areas where food, water and moisture are present, usually the kitchen, laundry room and bathrooms. Food cabinets, drain pipes, faucets, showerheads, underneath stoves and behind microwave ovens, etc., need to be inspected. You may want to employ the use of a non-toxic food substance (such as jelly) to place out in areas where the ants are suspected to be foraging to determine if indeed Pharaoh ants are the culprit. This method will let you make a positive ID on the pest, plus you can replace non-toxic baits with baits that have active ingredients in them and start to control the population. It is important in any indoor inspection — but particularly so for this species — to interview the client or homeowner and have them show you where ants were seen foraging.

Although I previously have mentioned some common areas based on food water and shelter (the three things all living things need to survive) remember that this species can be almost anywhere in the structure. Finding Pharaoh ant key locations is the hardest and longest part of the job.

Finally, don’t forget the outside of the structure especially in southern states. Generally, Pharaoh ants can been seen trailing on/around exterior walls, gutters, potted plants, wall edges and windows. Although generally thought of as an "indoor-only" ant, inspecting and treating any activity found outside of the structure can help your long-term success in dealing with problematic Pharaoh ant calls.

PAVEMENT ANTS. This common ant species in the eastern United States can be found under almost any structure outdoors that provides a suitable nesting site. Pavement ants get their name from the mounds of soil they construct between slabs of a sidewalk or driveway. In the event of nest formation, worker ants neatly pile small mounds of soil 2 to 6 inches in diameter around a nest entrance in an inverted cone shape. Like the other ant species discussed in this article, pavement ants nests can be constructed underneath almost any object that contacts the ground, wood piles, wood debris and rocks are, of course, most common but any sort of refuse that provides shelter will do.

Pavement ants are great foragers and will travel upwards of 50 feet from the colony in search of food and water. They are also general feeders and readily feed on high protein (dead insects), high carbohydrates (sweets and honeydew) as well as lipids (greasy food particles). When pavement ants are active, nests that are difficult to locate can be found by placing small bits of food items near trailing ants and following workers back to the nest site. It’s quite common to see large groups of individual workers recruited to a dropped food item on the sidewalk, driveway or inside of the house on the floor. Pavement ants can enter the structure through almost any crack or crevice, doorways, foundation cracks, in between expansion joints, improperly sealed windows, etc. In the process of gaining entrance, ants may indeed displace soil, and the previously mentioned mounds or piles of soil present in these areas are a good sign of a pavement ant infestation. If pavement ants are suspected, all of the sites mentioned above should be thoroughly inspected.

Once inside these ants will trail along edges and corners and it may be necessary to pull back the carpet in a room to determine which direction and where the ants are traveling to and from. Pavement ants can also enter from plumbing origins such as a toilet, sink or bathtub. These sites should also be inspected, especially if there is a history of leaks or high moisture/water associated with them due to poor construction or neglect of a persistent leak. Look for either foraging ants or the telltale piles of soil to tell you that ants are indeed present. Many times you may get a call for ants in the dead of winter. Pavement ants will frequently stir during periods of extreme dryness or freezing in some structures in response to a search for moisture.

CONCLUSION. Capitalize on providing good detailed ant inspections in your residential accounts. These thorough inspections will build you and your technician’s knowledge of ant biology and behavior, and provide a professional image of your business in the client’s eyes. Finally, you’ll be poised to win big when battling these formidable pests.


Hedges, S.A. 1998. Field Guide for the Management of Structure-Infesting Ants, GIE Inc. Publishers. Cleveland, Ohio.

Holldobler, B. & Wilson, E.O. 1991. The Ants. Harvard University Press. Cambridge, Massachusetts.

Mallis, A. 1990. Handbook of Pest Control 7th Edition. Franzak & Foster Co. Cleveland, Ohio.

The author is a senior research scientist at SC Johnson & Son Inc., Racine, Wis., in the New Product Development Division of the company’s Worldwide Consumer Products Group.