Structural and Public Health Pests: Ants

Pest Management In and Around Structures October 13, 2009 Print Friendly and PDF
Structural and Public Health Pests

Structural and Public Health Pests



Several species of ants cause problems inside schools. Removing individual ants and using detergent and water to clean up any chemical (pheromone) recruitment trail can be immediately effective in stopping a limited invasion. This should be followed by identifying and sealing the point of entry as a permanent solution.

The key to solving persistent ant problems is proper identification of the species. After the problem ant has been identified, information on life cycle, preferred food, harborage and nesting sites and effective management options can be readily obtained.

Stinging ants are addressed with other stinging insects below. Carpenter ants are also addressed separately below.

Ants typically enter school buildings from a colony located outside the school building. In each colony, one to several queens produce workers who seek out food and water for the larvae in the colony. With the advent of warm weather in the spring, ant populations and the demand for food increase dramatically. It is during this time that ants are most commonly sighted and become a nuisance. Most nuisance ants do not damage structures. Their entry into buildings is entirely a response to the availability of food, water, warmth or sometimes to escape flooding.

Occasionally, in the spring or fall, an ant colony will send out winged ants, usually around the time of a rain. This is a temporary event and does not require intervention other than vacuuming up any ants present. These ants do not bite or sting but rather are looking for mates and will disperse. It is very important not to mistake these winged ants for termites and wrongly determine that the school needs to be treated for termites.

Table 1. Nuisance ant species most likely to be encountered in schools and other structures in search of food, water or shelter. Stinging ants are addressed with other stinging insects below.

Table 1

Common and species name Geographic distribution
Argentine ant, Linepithema humile Southeastern US and California
Acrobat ant, Crematogaster spp. Throughout the US
Big-headed ant, Pheidole spp. Eastern US from Canada to Florida
Crazy ant, Paratrechina longicornis Southeastern US from Florida to Texas
False honey ant, Prenolepis impairs Throughout the US
Ghost ant, Tapinoma melanocephalum Southern (tropical and sub-tropical) US
Little black ant, Monomorium minimum Throughout the US
Odorous house ant, Tapinoma sessile Throughout the US
Pavement ant, Tetramorium caespitum Eastern US from Canada to Florida
Pharaoh ant, Monomorium pharaonis Throughout the US
Pyramid ant, Dorymyrmex spp. Throughout the US, most common in southern states
Thief ant, Solenopsis molesta Throughout the US

Monitoring and inspection for nuisance ants

Identifying the problem ant is the most critical step to take to solve a persistent problem. Monitoring for nuisance ants to determine which species are present is primarily visual inspection for foraging individuals, trailing ants or colonies. Additionally, bait stations may be monitored for evidence of feeding. Adhesive-coated monitoring traps may also capture ants. Finally, index cards can be baited with honey or sugar-water solutions, peanut butter and/or vegetable oil to attract and capture ants to identify which species are active in a specific area. On arrival at a site, the technician can place these and then check and remove after 30 minutes. Individual ants captured for identification purposes should be held in a small vial to preserve key identifying characters and sent to experts for identification, e.g., to your local county extension office or regional or state extension specialist.

Inspection practices should include checking for vegetation touching buildings, mulch contacting foundations, trash cans or dumpsters placed too close to building entryways, exposed food, inadequate clean up of spilled food or drink, unrinsed recycling, unsealed openings through the building exterior and missing or damaged door sweeps and door and window seals. Nests can also often be located by visual inspection and/or following trailing ants.

Cultural and physical options for nuisance ant management

Cultural and mechanical management options are preferred and include prompt clean up of spills, proper food storage and waste handling, preventing access to water by fixing plumbing leaks and repairing damp wood, eliminating harborage and access to the building by sealing cracks and crevices, and trimming vegetation and moving mulch away from buildings.

Many ant species leave behind a pheromone trail to recruit other ants to food and water sources. Small numbers of ants can be wiped up with a soapy sponge and washed down the drain. Care should be taken to wipe any trails that ants may be following with soap and water to eliminate any recruitment pheromones. This should be followed by identifying and sealing the point of entry as a permanent solution. Finally, exterior lighting should be positioned to avoid attracting crawling and flying insects to building entryways at night, which can then attract ants and other pests to these entryways to feed on dead insects.

Cultural and physical strategies for nuisance ants.

  • Remove individual ants using a vacuum or wipe.
  • Use detergent and water to clean surfaces where ants have been traveling to eliminate any pheromone recruitment trail.
  • Eliminate the access point where ants are entering by sealing cracks, installing door sweeps, repairing door and window seals, etc.
  • Clean up food and drink spills immediately.
  • Store food items in sealed containers.
  • Use liners for waste containers and empty at the end of the day so that food is not left in the building overnight.
  • Place exterior trash cans and dumpsters away from building entrances.
  • Fix plumbing leaks, gutters that hold water and damp wood to eliminate access to water.
  • Trim vegetation away from buildings to prevent ant access.
  • Rake back mulch at least 6" from building foundations to ease inspection for ant trails.
  • Position exterior lighting to avoid attracting crawling and flying insects to building entryways at night.
  • Use sodium vapor or yellow bulbs for exterior lighting to reduce attraction to insects.

A limited number of non-chemical products are used for nuisance ants including monitoring devices, sealants and exclusion devices.

Table 2. Commonly used products for physical, cultural or mechanical management of nuisance ants and their uses.

Type Example Products Uses
door sweeps and seals Sealeze Weatherseal Install to close gap between bottom of door and sill, and between edges of door and frame.
index cards baited with honey, peanut butter or vegetable oil Place on ground near building, e.g., where ants have been reported, check in 30 minutes to help identify problem species.
insect monitors Catchmaster® Insect Trap and Monitor Trapper® Monitor and Insect Trap Victor® Insect Glue Trap Continuous monitoring of ants and other arthropods.
reusable bait stations Ant Café Reusable Insect Bait Station AntPro® Ant Bait Station Kness Ants-No More Ant Bait Station Installed indoors. Installed outdoors, e.g., on a stake driven into the ground.
sealants many Close potential entryways.

Pesticide options for nuisance ants

Pesticides should not be used on a routine or calendar-based schedule but only where persistent ant problems occur, the ant species has been identified and non-chemical approaches have proven unsuccessful or uneconomical, e.g., repairs to old structures to exclude ants are not affordable.

Pesticide options that reduce potential for exposure include insecticide baits in pre-manufactured, enclosed bait stations and gel or liquid baits placed in cracks and crevices. Effective baits are available for most nuisance ant species.

Pesticide options that increase potential for exposure for students, staff and other facility users include spray formulations applied to exposed surfaces or broadcast granulars. These formulations are typically not required for successful management of nuisance ants in schools. Danger or Warning-labeled pesticides are not required for nuisance ant management. In addition, barrier applications to exposed impervious surfaces including foundations, walkways and driveways are prone to runoff into surface water and should be avoided.

Table 3. Commonly used insecticide products for nuisance ants and their uses.

a. Insecticides carrying a CAUTION label or exempt from EPA registration, in formulations that reduce potential for exposure.

Active ingredient Example products Uses
disodium octaborate tetrahydrate Indoxacarb Ant X® 739-12-2 Drax® Gel 9444-131 Intice™ Ant Gel 73079-1 Pre-manufactured enclosed bait station that can be placed in inaccessible areas.
boric acid, orthoboric acid Ant X® 739-12-2 Drax® Gel 9444-131 Intice™ Ant Gel 73079-1 Pro-Joe® Ant Bait 54452-7 Solution or gel that can be applied as drops in inaccessible areas where bait stations do not fit. Wipe up any over-application.
borax Terro® Ant Killer II 149-8
disodium octaborate tetrahydrate Gourmet Ant Bait Gel 73766-1
Indoxacarb Advion® Ant Bait Gel 352-746

b. CAUTION-label or exempt formulations with greater potential for exposure.

Active ingredient Example products Uses
fipronil Maxforce® Prof Insect Control Ant Bait Station 432-1256 Volatile active ingredient in pre-manufactured enclosed bait station. Use alternative non-volatile products.
sulfluramid Prescription Treatment Advance® Dual Choice Ant Bait Stations 499-459 Same as above
boric acid Borid® 9444-195 Dust formulation. To reduce exposure hazard, use alternative formulations if available, use only in voids that will be sealed after use or apply to surfaces in inaccessible areas. Wipe up any over-application.
diatomaceous earth Eaton‘s KOI System 56-67 Same as above
disodium octaborate tetrahydrate Boracide® 64405-7 Same as above
limestone NIC 235 Pro Organic® (EPA Exempt) Same as above
boric acid Prescription Treatment® 240 Permadust® 499-384 Pressurized aerosol formulation. Boric acid will leave dust residual. To reduce exposure hazard, use alternative formulations if available (Table 3 a), use in voids that will be sealed after use or apply to inaccessible areas. Botanicals must be applied directly to insects (no residual activity). To reduce respiratory exposure, use outdoors.
mint oil Earthcare® Naturals Ant & Roach Killer (EPA Exempt) Victor® Poison-Free Insect Killer (EPA Exempt) Same as above
2-phenethyl propionate, eugenol EcoEXEMPT KO Same as above
boric acid ECO 2000-GR® 1677-191 Niban® FG 64405-2 Granular formulations which may be broadcast on ground. Granular formulations have potential to be picked up by non-target organisms. Apply only when ants are actively foraging and restrict reentry until granules are removed by ants.
orthoboric acid Intice® Ant Granules 73079-2 Same as above

c. CAUTION-label formulations with greater potential for toxicity and/or exposure.

Active ingredient Example products Uses
bifenthrin Talstar® One 279-3206 Liquids sprayed or otherwise applied to exposed interior and/or exterior surfaces. Spray applications can contaminate an area and make baiting ineffective until the residue degrades. To reduce exposure hazard and avoid contamination, use alternative formulations (Table 3 a).
boric acid Mop-Up® 9444-132 Same as above
chlorfenapyr Phantom® 241-392 Same as above
cyfluthrin Tempo® SC Ultra 11556-124 Same as above
deltamethrin Suspend® SC 432-763 Same as above

Emerging issues, new strategies and priorities for nuisance ants

Argentine and other ants may be tempted away from areas where they are causing a problem by ―bribery‖ or ―diversionary baiting.‖ This strategy involves regular maintenance of bait stations placed outside and away from buildings, e.g., on the perimeter of a property. Starting by placing the baits outside and adjacent to the building, baits can be gradually moved out to the perimeter, drawing ant activity with them.

Granular formulations of botanical pesticides are broadcast around foundations to reduce ant activity. More information is needed on efficacy for specific ant species including residual activity.

Pyrethroids have been found at levels of concern in sediment of surface water in urban and suburban environments and associated with impacts on aquatic organisms. Other pesticides widely used for barrier perimeter treatments for ants including fipronil are also being examined for these potential hazards.

Priorities for nuisance ants.

  • Efficacy of botanical pesticide products on nuisance ants including use along dripline of structures where nuisance ant activity is present.
  • Efficacy of and optimum methods for diversionary baiting, e.g., baiting along perimeter of properties, away from structures, to reduce nuisance ant movement into structures.
  • Alternatives for perimeter barrier treatments of residual insecticides for ants that are toxic to aquatic organisms and have potential for runoff into surface water.
  • Education
  • Support materials for PMPs and others on effective diversionary baiting strategies.

Additional resources for nuisance ant management

Arizona Cooperative Extension. 2004. Ants. Pest Press. (PDF)

Daar, S., T. Drlik, H. Olkowski and W. Olkowski. 1997. Chapter 5. IPM for ants in schools. Pp. 27-34. In IPM for Schools: A How-to Manual. US EPA. Line drawings, identification, communication, monitoring, management.

Flint, M.L., ed. 2000. Pests of Home and Landscape. University of California Statewide IPM Project. Color images, description, biology and management. Available at

Hedges, S.A. 1992. Field Guide for the Management of Structure-Infesting Ants. 155 pp. Color and B&W photos, line drawings, identification keys, biology, management. Available from GIE Media, Richfield, OH (800) 456-0707.

Hedges, S.A. 1997. Chapter 12. Ants. Pp. 503-589. In Handbook of Pest Control, A. Mallis, ed. Color and B&W photos, line drawings, identification keys, biology, management. Available from GIE Media, Richfield, OH (800) 456-0707.

Klotz, J., D. Williams, B. Reid, K. Vail and P. Koehler. Ant Trails: A Key to Management with Baits.

National Park Service. 2003. Ants. In Integrated Pest Management Manual.

University of Florida. 1998. IPM for Ants in Schools.

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This work is supported by the USDA National Institute of Food and Agriculture, New Technologies for Ag Extension project.