Photograph of fire ants by Scott Bauer.
Widely disliked for their venomous, painful stings, fire ants have spread across much of the southern United States.
Source: http://www.ars.usda.gov/is/graphics/photos/
Image URL: http://en.wikipedia.org/wiki/Image:Fire_ants02.jpg

Red imported fire ant, Solenopsis invicta
Range: Americas, Southern China, Australia
Fire ants are aggressive and have a painful sting. A person typically encounters fire ants by inadvertently stepping into one of their mounds, which causes the ants to swarm up the person's legs, attacking en masse. The ants respond to pheromones that are released by the first ant to attack. The ants then swarm and immediately sting when any movement is sensed.