Fatal electrical attraction: Invasion of the insects from Hell

Electrical Apparatus, Sep 1997 by Elsberry, Richard B

They are on the march from the Deep South to the heartland of America

THEY FORAGE AS THEY GO, ravaging valuable crops. The U.S. Department of Agriculture currently rates them No. 22 on its list of public enemies, even though they are established in only 11 states. At every opportunity they fanatically make obeisance to their deities-ac and d-c electric fields. Electric fields are a fatal attraction, sending out a siren call that leads them to mob relays and switches, and then to remain lethargically next to their gods, enjoying a secret rapture, until they die of starvation or are electrocuted.

As they infest active electrical equipment they create short circuits by bridging terminal blocks, building nests and stripping-but not eatinginsulation from wires. They also enter mechanical switches and interfere with their action, causing malfunctions.

When disturbed by utility linemen, telephone technicians, appliance servicers, and plant electricians, they turn nasty and swarm to the attack. With pinching jaws and a bee-like sting, they inject a venom into their victims that produces a persistent burning sensation and raises small pustules. Estimates of the number of victims bitten annually range from three to five million.

These relentless invaders are solenopsis invicta Buren, the red imported fire ant, which arrived in Mobile, Ala., from Brazil in 1918, and currently infests some 400 million acres. (There is a less aggressive native red fire ant, solenopsis xyloni Mc Cook. )

The Gulf Coast states from Florida to Texas are the most heavily overrun, with imported fire ants today present in some areas in densities of 179 ants per square foot, or 7.8 million per acre. But invicta is on the march and has already moved north into Arkansas, Tennessee, Oklahoma, and the Carolinas. An outpost was recently discovered near Santa Barbara, Calif., and the small reddish-brown invaders are threatening to continue their relentless advance into Virginia, New Mexico, and Arizona.

Will fierce northern winters check their spread? It's likely, but no one knows for sure. Entomologists point out that many of the 8,803 ant species have not been deterred by sub-zero temperatures and consider it likely invicta will spread to all areas where winter temperatures remain above 10(deg)F.

While no one has yet translated the depredations of red fire ants into dollars, state highway departments already rate them a serious menace. The ants like to infiltrate traffic control cabinets where they get inside the flasher controls and strip insulation from control wiring, causing short circuits, which can result in potential tort liability claims. A service call to repair the damage averages $200.

In Texas, which has 15,000 traffic signals, a study conducted for the Department of Highways by Texas A&M University estimated that controlling the ants with insecticides would produce annual maintenance savings of $600,000.

The ants also have been a major factor in air conditioner failures. Service personnel in Texas have reported that fully one third of all summer repairs stem from ants shorting out terminal blocks. They also have been found to have set up housekeeping in televisions, well pump controls, telephone junction pedestals, airport runway lights, utility watthour meters, electrical plugs and lamp sockets, computers, and transformers-where they prefer to nest on the high-voltage side.

Why are imported red fire ants attracted to electric fields? No one is yet ready to offer a theory. But biologist Dr. William P. MacKay of the University of Texas at El Paso and entomologist Professor S. Bradleigh Vinson of Texas A&M have succeeded in eliminating a number of possible factors.

They have found fire ant behavior does not correlate with a-c frequencies, or with the presence of ozone, electromagnetic or magnetic fields. Nor is the type of insulation used on wiring a factor. In tests up to 140V a-c and 350V d-c, both attracted almost the same number of ants at the same voltage and distance. However, they did find that when electricity was turned off, ants attracted to d-c power dispersed more rapidly than those who had been experiencing the nirvana of an a-c source.

While the Texas researchers still don't understand the reasons why the ants have a fatal attraction to electric fields, they have been able to devise successful control techniques. Based on their studies, they recommend using terminal cap protectors to prevent bridging, and denying entrance to the insects by enclosing mechanical relays in metal or plastic cases and sealing them, as well as all entrances to padmounted equipment, with epoxy cement. In laboratory tests, silicone rubber sealants and roofing cement proved ineffective.

MacKay and Vinson also recommend applying insecticide annually to the interior of electrical equipment cabinets. While 157 chemicals have been registered as fire ant controls, they have tested three commonly used insecticides: 1,1,1 Trichloroethane; a combination of pyrethrin, piperonyl butoxide, and silica gel; and chlorpyrifos.