Humid Subtropical Zone The South Eastern United States, including the southern part of heaven, is classified as a Humid Subtropical Zone on global climate maps.  (See map right.)  Humid Subtropical Zones are characterized by warm temperatures, heavy precipitation, and they are, as the name implies, humid. While this environment can be challenging for humans over the summer, it’s sort of like nirvana for insects.  Here in the Southeast we expend a staggering amount of effort and money trying to alter the natural order things by enveloping ourselves in conditioned air and engaging in chemical warfare on our insect neighbors.

Insects evoke some of our deepest and most visceral fears.  Their shear numbers and seemingly relentless natures have provided fodder for many a disaster film.  My personal favorite, starring Joan Collins, was Empire of the Ants, released in 1977 and based on a short story by H.G. Wells.  As a bit of nostalgia, here is the movie poster.

empire of the ants The battle against insects in the Southeast parallels the development of the U.S. chemical industry which saw significant growth following World War I and thus provided ever more effective pesticides.  The initial results seemed impressive, with the most noteworthy outcome being the elimination of previously widespread malaria in the U.S. by 1949.  Unfortunately, this result came from voluminous application of the pesticide DDT, later found to be harmful to birds, including the American eagle.  Advances in pesticides also led to economic growth in the Southeast by facilitating the construction of long-lasting wooden structures here in our termite-friendly environment.

Despites our massive investments in pesticides and other control measures, the insects did not go gently into that goodnight.  Consider ants as an example.  The Red Fire Ant, native to South America, arrived in Texas in the 1930s.  Since then they have spread throughout the entire humid subtropical zone of the U.S.  Two or three colonies of fire ants take up residence in my yard each year.   I dislike using pesticides, but after a couple of episodes where I have ended up with multiple painful bites, I have succumbed and resorted to chemical warfare.

Recently the Red Fire Ant’s turf has been invaded by another native of South America, the Tawny Crazy Ant.  (Is that a great name or what? It’s based on their color as well as their rather convulsive body movements.)  The tawnies were first seen in the U.S. in Houston in 2002 and have since spread to Mississippi and Florida.  It is only a matter of time until they expand their range across the Humid Subtropical Zone.

Though lacking the painful bite of the fire ant, the tawny has some rather problematic characteristics.  They are two to three time larger than a fire ant and live in colonies with multiple queens which have populations 100 times greater than a fire ant colony. Although they are somewhat vulnerable to a couple of commercial termite pesticides, tawnies are not susceptible to any pesticides approved for consumer sale.  While fire ants tend to build their colonies in the ground and stay in their mounds unless distributed, tawnies like to colonize walls, crawlspaces, appliances, and, in particular, electrical cabinets where they chew through wires.

If you have ever had negative feeling about fire ants and hoped something bad would happen to them, I suppose you can now rejoice.  When tawnies move in, fire ants and other ants are wiped out.  Scientists are currently studying the details of the mechanism of this ant genocide. As with all invasive species, the invasion of the Tawny Crazy Ant is likely to have a series of negative impacts.  One which has become apparent already is the desiccation of grasslands in their territories leading to more problematic wildfires.

In the long run, our efforts to maintain a low-humidity, 66°F, insect-free Humid Subtropical Zone will fail and things will return to the way Mother Nature intended.  Want some further evidence?  Google mega mosquito.  In the mean time, we’ll keep up the fight.

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