Excerpts from Steve Tvedten's book "The Best Control
MONITORING AND THRESHOLDS FOR FIRE ANTS
The first step is to correctly identify the species of fire ants in the area. Population monitoring for fire ant control generally consists of determining the number of active mounds in a particular unit area. Any fire ant mound where at least three ants are observed after mound disturbance should be considered active. Heavily infested fields can contain over 100 active fire ant mounds per acre.
Another method of estimating fire ant populations for comparison studies is by collecting fire ants attracted at baits in a test area. A small piece of hamburger and a small piece of agar containing 40% honey are each placed on a small piece of aluminum foil or in a small plastic cup. The two baits are placed on the ground at each bait station, l’-3' apart, at each bait station. Bait stations are placed about 10 yards apart. The number of fire ant workers attracted to the baits per unit is monitored. Remember this mix if you decide to use baits to kill - mix in 5% or less boric acid or 3% or less sodium borate - keep out of reach of people and animals.
Fire Ant Threshold/Action Population Levels
The National Park Service has noted that threshold population levels for fire ants will vary according to the species and the sites. In certain camping and recreational areas, for example, very few active fire ant mounds per acre would likely be tolerated, particularly of the imported species. In contrast, a few active mounds per acre probably would be acceptable in other types of sites; little-used hiking areas, for example. Every effort should be made to correlate fire ant populations observed through the use of monitoring techniques with complaints received. In this way, a complaint threshold level can be established for each area.
In areas where fire ants are not causing any problems, the best solution is to do nothing. Some sites will only support a limited number of fire ants. These may be in the form of a few large colonies or many small ones. Established mounds defend territories, preventing the establishment of new colonies. Maintaining several large, and perhaps well-marked, colonies may be a sound way to stabilize fire ant populations in an area, as long as there is a low risk of people or pets stumbling into the nests.
Some researchers believe it may be best to selectively control fire ant colonies - allowing native species to flourish as a way to prevent the introduction of the imported species, or leaving single queen imports alone to prevent the area from invasion by a multiple-queen “supercolony.”
Mounds built by fire ants in fields often interfere with mowing and
farming operations. Not only is equipment damaged by dried and hardened
fire ant mounds, but operators may refuse to enter fields infested by ants.
The number of mounds per acre that can be tolerated as regards equipment
damage must be determined on a case-by-case basis.