There is general consensus that when fire ants and other ant species get shocked, they release pheromones that attract other worker ants to the site. Those workers also get shocked, release pheromones, and attract still more ants to the site.
As a result, switching mechanisms can get stuck "open" due to an accumulation of dead ant bodies, which allows the current to flow. How and why worker ants are initially attracted to electrical switches and similar situations where they get shocked is poorly understood. Their presence in these areas could be due to random foraging, or there may be something about electrical fields that attracts them.
Dr. Brad Vinson, Professor of Entomology at Texas A&M University, was involved with earlier lab studies that seemed to indicate that the ants have "an affinity" for electrical fields that makes them rest in those areas, thus making it more likely that they get shocked.
To keep fire ants out of electrical equipment, seal all sensitive electrical components, especially those that are not insulated. Examples are plastic housings containing contact points of switches, relays, and circuit breakers. Apply long-residual contact insecticides around housing, making sure to avoid the electrical circuitry or components. Treat the inside of equipment housings with products labeled for this use. Barrier-like pesticide strips are also available as a preventive measure. Proper placement of these strips is essential for adequate protection.
Regular inspections and treatment of nearby mounds, either individually or with broadcast bait applications over a surrounding area, will prevent fire ants from moving into the equipment boxes.
Find more information about fire ants in eXtension's Imported Fire Ant Resource Area.