Red Imported Fire Ants; Ant Colony Information; Q: How do I identify fire ants? Imported fire ants first came to the United States around 1930. Where do fire ants come from? Fire ants in your house: what you need to know. They are aggressive, particularly near the nest, and can inflict painful stings. Now there are five times more ants per acre in the United States than in their native South America. The painful sting of the fire ant’s bite is another good indicator, but not recommended as a method of identification. A: In areas where fire ants are commonly found, most people identify this pest by the appearance of the mound. They were accidentally introduced into the U.S. around the 1930’s through the port of Mobile, Alabama; probably in soil used for ships’ ballasts and have been spreading since. Red and black imported fire ants (Solenopsis invicta, and S. richteri) are native to South America. If you've spotted red ants in your home, don't automatically assume they are fire ants. The fire ants that came to the United States escaped their natural enemies and thrived in the southern landscape. Fire ants (Solenopsis invicta) are quite small (2-6mm) and come in an unusual variety of sizes within one nest.Their heads and bodies are coppery-brown and their abdomens are darker. However, in their search for food, they can come indoors through even the tiniest of openings.