200 CHAPTER 9 Sustaining Biodiversity: The Species Approach
The ants may have arrived on shiploads of lumber or
coffee imported from South America. Without natural
predators, fire ants have spread rapidly by land and wa-
ter (they can float) throughout the South, from Texas
to Florida and as far north as Tennessee and Virginia.When these ants invade an area, they can wipe out
as much as 90% of native ant populations. Mounds
containing fire ant colonies cover many farm fields and
invade people’s yards. Walk on one of these mounds,
and as many as 100,000 ants may swarm out of their
nest to attack you with painful and burning stings.
They have killed deer fawns, birds, livestock, pets, and
at least 80 people who were allergic to their venom. In
the United States, they also do an estimated $68,000
of economic damage per hour to crops and phone and
power lines.
Widespread pesticide spraying in the 1950s and
1960s temporarily reduced fire ant populations. But this
chemical warfare actually hastened the advance of the
rapidly multiplying fire ants by reducing populations of
many native ant species. Even worse, it promoted de-
velopment of genetic resistance to pesticides in the fire
ants through natural selection (Concept 4-2B,
p. 80). In other words, we helped wipe out
their competitors and made them more genetically re-
sistant to pesticides.
In the Everglades in the U.S. state of Florida, the
population of the huge Burmese python snake is in-
creasing. This native of Southeast Asia was imported
as a pet, and many ended up being dumped in the
Everglades by people who learned that, when they
get larger, pythons do not make good pets. They can
live 25 years, reach 6 meters (20 feet) in length, weigh
more than 90 kilograms (200 pounds), and have the
girth of a telephone pole. They have razor-sharp teeth
and can catch, squeeze to death, and swallow whole
practically anything that moves and is warm-blooded,
including raccoons, a variety of birds, and full-grown
deer. They are also known to have survived alligator
attacks. They are slowly spreading to other areas and,
by 2100, could be found in most of the southern half of
the continental United States.Figure 9-16 The Argentina fire ant, introduced accidentally into
Mobile, Alabama, in the 1930s from South America (green area),
has spread over much of the southern United States (red area). This
invader is also found in Puerto Rico, New Mexico, and California.
Question: How might this accidental introduction of fire ants have
been prevented? (Data from S. D. Porter, Agricultural Research
Service, U.S. Department of Agriculture)Image not available due to copyright restrictions