Pest Control: Ant Control – Quality Assurance & Food Safety

When thinking of pests that can be found in a food processing plant, ants are a little below the list of cockroaches, flies, food pests, spiders, and rodents. But outside of any building, including a food crop, ants are common residents. Most ant colonies stay outside, but given the right conditions, certain species can invade a food crop and look for additional resources or even additional nesting sites. Certain species of ants, such as the pharaoh ant, can infest a building by being carried inside or by hiding in boxes or other incoming supplies.

The type of ant that could cause a problem depends heavily on the geographic location of the plant. Few species of ants, such as street ants or fragrant house ants, may appear in a food processing facility in a northern state. Numerous species could be found in the south, especially along the Gulf Coast. Examples include Argentine ants, ghost ants, big head ants, fire ants, pharaoh ants, whitefoot ants, rover ants, and various types of crazy ants. In California and other western states, Argentine ants are the most likely pest species to encounter, although others can be seen in specific locations.

Identifying pest ant species can be difficult for a food factory worker, but specimens can be identified by the facility’s pest controller if one is employed. References such as the PCT Field Guide for the Management of Structure-Infesting Ants are available to help anyone identify pest ants that may be found in a building. Remember that there are many uninfected species of ants in landscapes and lawns and that these can potentially invade a building. In such cases, it may be necessary to send samples to the state university of entomology to identify ants that cannot be found in reference books.

It starts with the ant.

The first indication of ants in a food processing facility usually comes from an employee’s sighting of the ants. Typically, ants infestation come from outside and ants are spotted near outside walls. Occasionally, ants can be found deep within the facility. In any event, samples should be taken for identification as described above, as the species involved will often determine where to look for the source of the infestation and what control measures are best suited to control the situation.

Useful examples

Every situation and facility is different and may require a specialized approach based on the facility’s needs, but the following real-world examples from consultant Stoy A. Hedges relate to solving an ant infestation in food processing plants.

Case No. 1

A Florida grocery store was infested with common mad ants (Paratrechina longicornis). The ants came from outside beds along the foundation, where the ants nest in leaf litter that had accumulated under the bushes there. Leaf litter was raked out and ant colonies treated directly. The facility was advised to periodically remove the accumulation of leaf litter to prevent recurrence of ant problems.

Case No. 2

A pharmaceutical company in California saw Argentine ants in large numbers at the facility with occasional invasions inside. This facility has been beautifully landscaped with low maintenance grass plants and citrus trees near the building. Ants tended aphids for their honeydew on the trees and nestled in the grass plants and landscape mulch. In this case, liquid ant bait stations were installed around the building and at the base of each citrus tree. The constant maintenance of the liquid bait stations throughout the season led to a large reduction in the ant populations and enticed the ants to stay outside to look for food. Internal sightings of ants were no longer reported.

Case No. 3

A food factory in Wisconsin reported Argentine ant activity deep inside the building during the cold winter months. It was believed that the ants were carried into the building at some point during the replenishment and had settled inside the building. The pest controller succeeded in following the ants’ tracks back to a hollow block wall, where they penetrated through a small crack and also to an expansion joint in the slab floor. During a shutdown period, the hollow block wall was drilled in numerous places, a residual dust product was introduced into the cavities and the boreholes sealed. The active expansion joints were injected with a residual insecticide applied using a crack and crevice tip on the sprayer. The plant maintenance department then closed the expansion joint with a durable sealant.

For example, pharaoh ants will nest inside the building and bait is the best control strategy. Fire ants, on the other hand, nest in the ground and can forage long distances inside from colonies along the outer foundation. Fire ants are also known to nest on flat roofs of commercial buildings. Street ants nest under slab floors and penetrate through expansion joints. Large-headed ants are known to live in the soil of potted plants found in an office area. Other species, such as Argentine and fragrant house ants, nest mostly outdoors, but build sub-colonies indoors.

Effective inspections.

The key to quickly controlling an ant infestation is to locate and treat the colony or colonies directly. A lot of time can be spent looking for ant colonies, but a few tips can help make the inspection more effective.

Links: April Noble,,; right: © Eli Sarnat, Antkey, USDA APHIS PPQ,

1. Look for locations where the target ant is most likely to be found nesting. Ants nesting in the ground such as pavement, fire or large head ants can be found in the ground near the building or in the ground under a slab ceiling. Look for piles of displaced soil that indicate possible nesting sites. Inside, there may be displaced soil along expansion joints or behind equipment.

2. Follow the paths inside along the walls to points where ants can enter under the floor or through walls. If an area of ​​activity is carpeted, needle-nosed pliers can be used to pull the carpet up just enough to see if ants are dragging along the tack strip.

3. Use foods like swabs of jelly or honey to entice ants into recruiting for these foods and creating paths that are easier to follow. This technique can be used indoors and outdoors to determine if (and what types) of ants are present. Put these foods on index card squares for 10-30 minutes indoors, then check activity. In food areas, these placements should be removed and not left in place.

4. Focus on structural guidelines. Ant trails usually appear along corners and edges, e.g. B. along skirting boards, cracks, etc. If you are following an ant trail, look ahead where the structural guide breaks and go there to see if the trail continues. If not, go back to see where the path changed course. Try to follow the paths to the colony location where they enter the building.

5. For many species, if a colony is found, don’t stop looking. Many of our most troublesome ant species are polydomain, which means that the colony is made up of many nesting sites. The placement of food attractants (see # 3) can reveal species of ants that are not currently present.

6. Turn objects outside to look for colonies. Use a hand rake or other tool to rake through mulch and leaf litter, causing nesting ants to emerge and release colonies. It’s also a good idea to have a sprayer with you to treat colonies outdoors if they are revealed – disturbed colonies can relocate in minutes and disappear when you come back to treat them.

Target colonies.

Most ant plagues come from outside or are tied to off-site colonies. Exceptions are pharaoh ants, an occasional infestation deep inside a building, and one that can originate from a flat roof. As soon as the inspection has uncovered colony locations, these can be directed to direct treatment.

In the open air, a colony is controlled by soaking colonies with an appropriately labeled water-based product. Care should be taken to distribute it well and may require the use of a tool to move mulch, soil, or leaf litter to facilitate penetration. Large colonies, such as fire ants, require larger amounts of product for satisfactory control.

Fire ant infestations in landscape and lawn areas can also be treated with granulate baits. For facilities in areas of endemic fire ant activity, widespread use of fire ant bait early in spring can help minimize the number of anthills that occur during the season.

Within a food processing plant, the use of residual products may be restricted or not recommended, especially in processing, packaging and similar food areas. The rest of the treatment can be carried out directly in the wall cavities or under panels, with any drill holes being closed after application. Ant trails leading back to the treated outer colonies can be treated with a contact insecticide and the treated areas cleaned before operations resume. A soapy cloth can also be used to wipe away internal ant marks after the colonies have been treated.

If the colony cannot be located indoors, ant baits can be used in refillable stations in areas where there is activity. Note that such stations in food processing / packaging areas can only stand still when the area is not in use and must be removed when operations resume. In these cases, frequent checks of the stations during use are recommended to determine bait acceptance, and other types of bait are substituted if the target ants ignore the bait. Repeated bait placement when the area is idle should be done until ant activity ceases and / or the offending ant colony has been definitively located and treated.

The author is the owner of Stoy Pest Consulting and one of the leading urban entomologists in the country and author of several books.

To order the PCT Field Guide for the Management of Structure-Infesting Ants, call 800-456-0707, visit or send an email to [email protected] The 325-page third issue costs $ 9.95.

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