At times ants seem omnipresent. They can literally be anywhere and everywhere. Of course, when dealing with ants, and any pest problem, it is best to identify the pest species you’re dealing with. This is so because the biology and behavior of the individual pest may vary or be significantly different than other pests. Additionally, the control strategies implemented are usually tailored to the biology and behavior of the target pest species.

Below is a field case study regarding an ant problem occurring at a hospital. The concepts and methodologies successfully implemented to resolve this ant problem may be utilized in other situations as well.

Feel free to post your ant or other pest questions on our Ask the Expert page.

Good luck !


Case Study: Solving a Long Term Serious Ant Problem

By: Paul J. Bello, President
PJB Pest Management Consulting

Date: August 14, 2017

A call arrived from a local hospital where Argentine ants had been a long term problem. As usual with this species, the ants were seen trailing in kitchen, pantry and break room areas where they foraged for food and numerous ants were frequently observed as they trailed to various locations.

Ants are generally viewed as tolerable insect intruders in comparison to cockroaches, which are usually seen as being disgusting. It was when these ants made their way to the cardiac intensive care unit that the problem became serious enough to garner the attention of management.

The section of the hospital where this problem was happening involved five stacked floors. According to staff representatives Ants had been a continued problem here for at least two years. The problem was regarded as serious when ants were found foraging on patient beds, intravenous lines and patients themselves in the ICU. In fact, the problem was so significant that two entire ICU floors were vacated and patients relocated. This is what prompted the call.

Of course, the first step in resolving a pest problem is the correct identification of the target pest. These ants had been previously identified as Odorous House ants but the ants observed here were Argentine ants. These ant species are similar in appearance and behavior. While a misidentification would be incorrect, their behavior would be close enough such that the control methodologies would be similar for both.

The hospital staff had explained that “they’ve done everything” to get rid of these ants and that “nothing was working”. Review of the treatment records indicated that hundreds of gallons of insecticide had been applied both indoors and out. The staff stated that they had weekly “power sprays” done around the outside of the building for the past eight weeks yet the ant problem continued.

Experienced pest professionals already know that individual ants are relatively easy to kill. As such, consideration of the available information would lead one to a thought process which would consider; if all this work was being done correctly, what’s going wrong and why are we still seeing so many ants?

Under such circumstances it is wise to question and consider what factors are being missed, what are the various possibilities and how might the known biology and behavior of these pests affect the situation. Such themes are useful when working to resolve problematic pest situations.

During the inspection of the facility things just didn’t add up. Something was going wrong and my suspicions could be confirmed with relatively little effort and time if only the ants would cooperate.

As you may know, Argentine ants are a type of tramp ant. These ants utilize pheromones, or chemical signals, to establish forage trails to and from food resources and back to their nest locations. We know this trailing is part of their normal behavior and we can use this behavior against them.

The staff informed me of several areas where ants were being seen on a daily basis. Jelly packets “borrowed” from the hospital cafeteria were opened and placed in a few areas for the ants to find and we went on a lunch break. Given sufficient time the ants would establish forage trails to and from the jelly placements such that nest locations could be found.

As expected the ants had begun to feed on the jelly packs while we were at lunch. Heavily traveled forage trails of ants were easily seen. What was unexpected was what was learned when following these trails. At just about 1/8th inch long these ants are small. As such, these ants can gain entry through doors, windows and wall voids which appear impassable. Here, these ants were trailing up the painted concrete block walls, across the window sill and through the window frames to the exterior.

A look out the window showed that the ant trails were headed upward and not down toward grade level. Looking out additional windows on floors above enabled us to see that the ants were headed up to the roof level. A trip to the roof was needed to inspect the roof area and see where these ants were going.

Like other commercial buildings this was a flat roofed structure. As commonly seen, the roof surfaces was covered with gravel. Beneath the gravel was a water proof bladder. Beneath the bladder were sheets of about four inch thick rigid foam board insulation. The ants had hollowed out galleries and nest locations within the foam board insulation. Once we knew where the nest locations were, the ants would soon be easily eliminated.

Note that the power spray applications to the building’s exterior perimeter would never control these ants because the source, or nest, was not being treated. Ant field research work conducted in the nineties provided the basis and experience for tracking ants using suitable baits. Trailing or tracking ants using this technique can be successfully used to your advantage to resolve ant problems when needed.