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Fire ants invade and evolve
by the Understanding Evolution team

In the late 1930s, a small but threatening invader arrived in the United States: the Argentine fire ant (Solenopsis invicta). Having hitched a ride from its homeland, S. invicta set up outposts in Alabama — nests inhabited by thousands (and sometimes hundreds of thousands) of tiny red workers (all female — males just hang around for reproductive purposes) and single queens. Over the next 20 years, S. invicta spread throughout the South, inflicting painful stings, building large nests, and generally annoying human populations.

At left, workers tend to the queen in a single-queen colony. At right, a pasture dotted with numerous fire ant nests.

What is it about S. invicta that's made their U.S. invasion so successful? As it turns out, the answer is an evolutionary one.

	In this case study we will explore these key questions: How does natural selection work? How does natural selection favor different genes based on environmental conditions? How can a simple gene affect complex behavior? How can understanding the natural and evolutionary history of fire ants help us to slow their invasion?