Photo by A. Wild, Wikimedia Commons
(Many thanks to Chris Urik, one of my old students, for keeping my interest in fire ants alive!)
There aren’t any fire ants in Western Pennsylvania, and even if there were they would not be active in the winter. If fact, it is our winter that keeps fire ants from invading our yards and fields (Tennessee is farthest north the fire ants can go before the prolonged and intense cold of the winter kills the colonies. Who knows what will happen with on-going global warming, though?).
Anyway, I am just using this winter period to reminisce about my interactions with fire ants and think about some of the newest research concerning them.
I first encountered fire ants in southeastern Texas in 1970. I was camping near Lake Corpus Christi and since the night was warm and humid I was sleeping out on tarp near the lake shore. A breeze kept the mosquitoes down, and I had just fallen asleep when all of sudden my arm and leg were set upon by a stinging swarm of tiny attackers. I had spread out my tarp near a fire ant nest and the foragers were coming out to look for food and to deal with intruders. I jumped into the lake not caring about the water moccasins I had seen earlier in the day and washed the ants off. There were no alligators in Lake Corpus Christi then (there are some now thanks to the on-going, Texas recovery of the species!) but I would not have cared about them either. I can still vividly remember the pain of those stings and the fight-or-flight panic they triggered!
Fire ant colony. Photo by M. LaBar, Flickr
Red imported fire ants (“RIFA,” or Solenopsis invicta) were first identified in Alabama in the 1930’s. They undoubtedly entered the United States via the seaport in Mobile. Recent analysis of their DNA indicates that these ants are from a northern province of Argentina. Natural dispersal mechanisms (seasonally generated, winged alates) and human-assisted dispersal mechanisms (including the transport of plants with infested root balls, shipments of grass sod and soil, and the long distance movement of many other types of agricultural products) facilitated their rapid spread across the continent. They are now found in fourteen states stretching from Georgia all the way to California.
For the most part control and eradication methods have been ineffective against RIFA’s. The pesticide Mirex was specifically used against them from 1962 to 1975 but with little impact. The toxicity of the Mirex and its high rate of accumulation in biological tissues turned out to be an even more severe environmental problem than the fire ants themselves! Mirex manufacturing and use was banned in 1978. One of the reasons that neither chemical control nor physical control (fire or flooding) are effective against RIFA’s is that each colony contains multiple queens. The survival of even one of these queens enables the ants to quickly re-establish a colony in nearby locations.
Fire ants are very aggressive and will kill not only the native ant species they encounter but also many other insect species. They can make a pasture unusable by grazing animals and can even make the use of agricultural machinery impossible in heavily infested fields.
Photo by M. Klassen, Pixabay
Fifteen years ago RIFA invaded Hong Kong, and they have since spread throughout the province’s urban and rural habitats (see November 1, 2017 article in The Scientist). These ants have established themselves in the extensive parkland of Hong Kong and also have made colonies under concrete sidewalks and streets and even inside of electrical equipment. Pesticides have been used on specific colonies of these ants, but authorities recognize that they will not be able to eradicate them but only control their eventual distribution. Taiwan also has an extensive, established population of invasive fire ants, and they have also been reported at several seaport sites in Japan. So far, though, no colonies have been established in Japan.
Fire ants are extremely adaptive and resilient. A single queen arriving in stored cargo is enough to establish a massive ant invasion. It is thought that the multiple queening seen in the fire ant colonies in the United States is an adaptation to attempts at population control using pesticides. Also, the Argentinian province from which they originate is prone to flooding, so fire ants have evolved the ability to form large, interconnected floating masses of individuals by which they ride out the flood. These fire ant masses were seen in the Houston area this summer following the flooding from Hurricane Harvey. Also, fire ants can merge small colonies into larger and larger “super” colonies, and, thus, more easily overwhelm their competitors and not waste their energies competing with each other.
Photo by Bentleypkt, Wikimedia Commons
Another invasive ant species from Argentina, though, is beginning to interfere with the dominance of fire ants in the Gulf Coast region of the United States (Science (February 28, 2014)). This new ant (the “tawny crazy ant” (Nylanderia fulva) (the name “crazy” comes from the erratic patterns of movement exhibited by individuals of this species) is able to coat itself with its own formic acid-rich secretions and, thus, denature many of the proteins in the fire ant’s venom. The functional loss of these proteins makes the venom less effective and enables the tawny crazy ant to out-compete and even destroy the previously nearly invincible RIFA. The tawny crazy ant is from the same Argentinian province as the RIFA and it is thought that its secretory and behavioral specializations came about after a long evolutionary history of RIFA encounters.
The venom of the fire ant contains a group of chemicals called “solenopsins” (a term derived from the genus name of the RIFA). Medical research into the therapeutic uses of these solenopsins have revealed several interesting potential applications. Researchers at Emory University and Case Western Reserve in a paper published in Scientific Reports (September 11, 2017) reported that solenopsins help to reduce skin thickening and inflammation in mouse models of psoriasis. They can also inhibit the formation of new blood vessels and may thus be useful as anti-cancer medications. There might be some considerable human health benefits, then, from these destructive, invasive ants!
I am very glad that we don’t have fire ants here in Western Pennsylvania! We have to deal with brown, marmorated stink bugs, gypsy moths, emerald ash borers, spotted lantern flies, wooly adelgids, and many more invasive insects. None of them, though, would make me jump into a lake full of water moccasins!