- Argentine ant Linepithema humile
- Pharaoh ant Monomorium pharaonis
- Bigheaded ant Pheidole spp.
- Odorous house ants Tapinoma sessile
- Crazy Ant Paratrechina longicornis and Nylanderia spp
Generally small (less than 1/8 inch), persistent and abundant ants that are commonly attracted to various kitchen and classroom foods, including sweets, oils and proteins. Tramp ants are usually non-territorial, quick to spread and often found many small nests. They represent some of the most common and important indoor and outdoor nuisance ants. Odorous house ants and Argentine ants have a pungent odor when crushed. The smallest of these ants include the Pharaoh ant and rover ants. Each ant species has its own unique biology, food preferences and control methods, so identification can be critical to selecting the best control. The following are general guidelines for dealing with tramp ants/nuisance.
Several species of ants cause problems inside schools. Ants are social insects. Their nests or colonies can be found indoors and out, although some species have preferred nesting sites. A nest contains one or more queen ants laying eggs and being cared for by worker ants. Worker ants-- sterile or non-reproductive female ants--tend the queen and brood (eggs, larvae and pupae) and forage for food. Foraging ants can invade buildings from colonies outdoors.
Nests often can be located by following "trails" of foraging ants. Indoors, ants nest almost anywhere. For instance, Pharaoh ants readily nest in attics, appliances, linens, heating ducts, wall voids and light switches or fixtures. Killing foraging ants rarely solves an ant problem in the home because the colony remains unaffected.
During certain times of the year, most species produce reproductive’s, winged male and female ants that leave the nest to mate and establish new colonies. When winged ants swarm inside, their colony is likely to be located somewhere inside.
Ants form new colonies in several ways. Most are started by a newly mated, winged reproductive, now called the queen. After finding a suitable nesting site, the queen loses her wings and begins laying eggs, which hatch into legless, grub-like larvae. The queen feeds the larvae as they develop through several stages in which they molt and grow between each stage. Afterward, they form pupae and soon emerge as adult ants. The eggs, larvae and pupae are often referred to as “brood”. Once worker ants have developed, the queen no longer needs to care for the brood. The brood is cared for by worker ants. Cooperative brood care is important to successful baiting because this is one way bait toxicants can be passed through a colony.
Some ant colonies have more than one queen, and mating may occur within the nest without swarming. These ants form new colonies when one or more queen ants, along with some workers and brood, leave the nest and move to a new location. Ant colonies do not nest in permanent locations; frequently entire colonies move from one nesting site to another almost overnight. Particularly during very wet or abnormally hot and dry weather, ant colonies whose nesting areas are flooded or lack food and water often migrate indoors. It is not uncommon to receive complaints about ants after a heavy rain. Worker ants foraging for food and water become a concern when they infest food or other items in the structure. Although most ants consume a wide variety of foods (they are omnivorous), certain species prefer some types of foods and some even change their preferences over time. When baiting ants that can change their diet preference, it is important confirm that the ants are feeding on bait being offered. So, if the ants are not feeding on protein-based bait, try sweet-based bait. Foraging workers of some ants establish temporary chemical (pheromone) trails that help other ants find food and water. These species can "recruit" other ants to a resource quickly and in high numbers. Food is brought back to the colony and fed communally among the other members of the colony, including the queen(s) and brood, a process called trophallaxis.
Suggested Thresholds First sign of ant trails consisting of 6 or more ants. When only winged (reproductive) ants are present in such sites, no treatment is probably necessary. However, the IPM technician should be consulted to ensure that such insects are not confused with termites.
Monitoring and Inspection
- Identifying the problem ant is the most critical step 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 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. To find your local agent or specialist go to www.nifa.usda.gov/Extension/index.html
- 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.
Nonchemical Control Measures
Sanitation/Cultural Control Measures
- Disrupt ant trails by applying District-approved all purpose cleaners. Wash trails with cleaner to remove scents that ants use to return to a site with food.
- Preferred management options 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.
- 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.
Physical/Mechanical Control Measures
- Remove individual ants using a vacuum or wipe or wash away.
- Eliminate the access point where ants are entering by sealing cracks, installing door sweeps, repairing door and window seals, etc.
- 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.
Chemical Control Measures
- At times, non-chemical methods alone prove insufficient to solve the problem. Integrating a pesticide into your management program may be necessary to gain control of the ant problem.
- Pesticides must be used in accordance with their EPA-approved label directions. Applicators must be certified to apply pesticides and should always wear protective equipment during applications. All labels and Material Safety Data Sheets (MSDS) for the pesticide products authorized for use in the IPM program should be maintained on file. Do not apply these materials when buildings are occupied, and never apply them where they might wash into drains or sewers.
- When treating ants, all baits and dusts should be placed in cracks, crevices, and in precise areas where ants are active.
- Insecticide-impregnated plastic barriers can also be used to protect inaccessible wiring and electrical boxes.
Baits greatly reduce the amount of pesticide that must be used to kill ants. Foraging ants take the bait back to the nest to feed to other members of the colony resulting in colony death. Even if the queen is not killed, baits will usually stop an ant invasion. If a colony has been starved by effective sanitation measures, baits will be more readily accepted.
Always place baits out of sight and reach of children, or, if this is not possible, use baits at night or on weekends and remove when children are in school. Some ants are very susceptible to baits, some are less so. There are many reasons for these differences, only some of which we understand. If you are having difficulty in controlling ants with bait, the following points may be helpful:
- It is important to correctly identify the species of ant that is invading the school since each species differs in its food preferences. Some baits contain a sweet attractant and others use a protein or oily attractant. Therefore, the attractant in the bait must be preferred by the type of ant identified. If you cannot determine the type of attractant by looking at the label, call the manufacturer for more information. You should also ask if the company has data to support the efficacy of their product against the ant species you are dealing with.
- After setting out bait, observe to see if the target ant is taking the bait.
- Ant colonies have changing nutritional requirements that can pose problems in baiting. A colony that accepted protein bait one week may be more interested in sugar bait the next.
- The nesting and foraging environment can also affect bait acceptance. Ants nesting and foraging in dry areas will be more interested in baits with high water content than will ants nesting in moist environments.
- When there are several competing ant species in one area, non-target ants may accept your bait more readily than the pest ant and, in some cases, prevent the pest ant from getting to the bait.
- Do not spray pesticides when using baits. Bait stations contaminated with pesticide are repellent to ants, and sprays disperse the ant infestation, making it more difficult to place baits effectively.
- Place bait stations along foraging trails, but do not disturb ant trails between the nest and the bait. Killing the ants or disturbing the trails prevents the ants from taking the bait back to the colony to kill nest mates.
- Do not apply bait until an ant problem is noticed. If you use baits preventively you may attract ants into the building.
- Some baits come packaged in plastic disc "bait stations" that comes with double-sided tape so they can be attached to various surfaces out of view. It is important to remove bait stations once control is attained because the stations may serve as harborage for cockroaches. Some baits are formulated as granules or gels that can be injected into wall voids through small holes. Gel baits can also be placed near ant trails in inconspicuous places where they will not be disturbed.
When using bait methods allow approximately 6 to 8 weeks for effective population reduction.
Authors: Compiled from publications by Mike Merchant, Karen Vail, Faith Oi, S. Darr, T. Drlik, H. Olkowski, and W. Olkowski