Repeated ant image: © Stoy A. Hedges

When one thinks of pests that may be found inside a food processing plant, ants are a bit down the list from cockroaches, flies, stored product pests, spiders and rodents. Yet, outside any building, including a food plant, ants are common inhabitants. Most ant colonies remain outside, but under the right conditions, certain species might invade a food plant searching for additional resources or even additional nesting sites. Certain ant species such as the Pharaoh ant can infest a building by being carried inside or hiding in boxes or other incoming supplies.

Which ant species might cause a problem depends largely on the geographic location of the plant. A food processing facility in a northern state may only encounter a couple of ant species, such as pavement ants or odorous house ants. In the south, especially along the Gulf Coast, numerous species could be encountered. Examples include Argentine ants, ghost ants, big-headed ants, fire ants, Pharaoh ants, white-footed ants, rover ants and several species of crazy ants. In California and other western states, Argentine ants are the most likely pest species encountered, although others may be seen in certain locales.

Identification of pest ant species may prove difficult for employees of a food plant, but specimens can be identified by the facility’s pest professional, if one is employed. References such as the “PCT Field Guide for the Management of Structure-Infesting Ants” are available to assist anyone in identification of pest ants that may be encountered in a building. Keep in mind that many non-structure-infesting ant species occur in landscapes and lawns and any of these could potentially wander into a building. In such cases, sending specimens to the state entomology university may be necessary to obtain identification of ants not found in reference guides.

It Starts with the Ant.

The first indication of ants inside a food processing facility will usually come via an employee sighting of the ants. Typically, ant infestations will originate from outside and sightings of ants will be near exterior walls. Occasionally, ants may be found deep within the facility. In either case, specimens should be collected for identification as discussed above as the species involved often determines where to search for the source of the infestation and what control measures may be best to control the situation.

For example, Pharaoh ants will be nesting within the building and baiting is the best control strategy. Fire ants, by contrast, nest in the soil and can forage long distances inside from colonies located along the exterior foundation. Fire ants are also known to nest on flat roofs of commercial buildings. Pavement ants will nest under slab floors and enter through expansion joints. Big-headed ants are known to be carried inside living in the soil of potted plants that might be found in an office area. Other species such as Argentine and odorous house ants nest primarily outside but will establish sub colonies indoors.

Effective Inspections.

The key to quick control of 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 for a more effective inspection.

Left: April Noble, Antweb.org, Bugwood.org; right: © Eli Sarnat, Antkey, USDA APHIS PPQ, Bugwood.org

1. Search sites where the target ant is most likely to be found nesting. For example, soil-nesting ants such as pavement, fire or big-headed ants will be found in the ground outside near the building or in the soil beneath a slab floor. Look for piles of displaced soil which indicate possible nest sites. Inside, displaced soil may be found along expansion joints or behind equipment.

2. Follow trails inside along walls to points where ants may be entering from under the floor or through walls. If an area with activity is carpeted, a pair of needle-nose pliers can be used to pull up the carpet just enough to see if ants are trailing along the tack strip.

3. Use foods, such as dabs of jelly or honey to entice ants to recruit to those foods and establish trails that are more easily followed. This technique can be used inside and outside to determine if (and which kinds) ants are present. Indoors, place dabs of these foods on squares of index cards for 10-30 minutes, then check for activity. In food areas, these placements should be removed and not left in place.

4. Focus on looking at structural guidelines. Ant trails mostly occur along corners and edges such as along baseboards, cracks, etc. When following an ant trail, look ahead to where the structural guideline breaks and go there to see if the trail continues. If not, backtrack to see where the trail did alter course. Attempt to follow trails to colony location where they enter the building.

5. With many species, don’t stop looking when one colony is found. Many of our most troublesome ant species are polydomous, meaning the colony consists of many nest sites. Food attractant placements (see No. 3) can reveal ant species that are currently unknown to be present.

6. Outside, turn over items to look for colonies. Use a hand rake or other tool to rake through mulch and leaf litter, causing nesting ants to emerge and reveal colony locations. Also, it is a good idea to carry a sprayer to treat outdoor colonies as they are uncovered — disturbed colonies can relocate in a matter of minutes and be gone by the time you return to treat them.

Target Colonies.

Most all ant infestations originate from outside or are tied to exterior-located colonies. Exceptions include Pharaoh ants, an occasional infestation deep within a building and one that may be originating from a flat roof top. Once the inspection has revealed colony locations, these can be targeted for direct treatment.

Outdoors, drenching of colonies using an appropriately labeled, water-based product will control a colony. Care should be taken to ensure good distribution and may require using a tool to move mulch, soil or leaf litter to aid penetration. Large colonies, such as fire ants, will require larger volumes of product for satisfactory control.

Fire ant infestations in landscaping and lawns may also be treated with granular baits. For facilities in areas with endemic fire ant activity, broad application of fire ant bait early in the spring can help minimize the number of ant mounds occurring through the season.

Inside a food processing facility, applications of residual products may be limited or not recommended, particularly in processing, packaging and similar food areas. Residual treatment may be applied directly into wall voids or underneath slabs, with any drill holes sealed following application. Ant trails leading back to exterior colonies that are treated may be treated with a contact insecticide and the treated areas cleaned before operations resume. A rag with soapy water can also be used to wipe away interior ant trails after colonies have been treated.

If the colony cannot be located indoors, ant baits placed in refillable stations may be used in areas where activity is present. Note that such stations can remain in place in food processing/packaging areas only when the area is not in operation and must be removed when operations resume. In these cases, frequent checks of stations while they are in use is recommended to determine bait acceptance, and other types of baits substituted if the target ants are ignoring the bait. Repeated placement of the baits whenever the area is not in operation should be implemented until ant activity ceases and/or the offending ant colony is finally located and treated.

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