Red imported fire ant

Solenopsis invicta, the red imported fire ant (Formicidae), is a small to medium-sized ant: workers measure 2.4–6.0 mm, queens 8–10 mm. Native to the Paraná River basin of South America, it reached Mobile, Alabama, in the 1930s and by 2004 occupied about 128 million hectares across thirteen southern US states; it has also spread to Queensland, Taiwan and southern China. Mounds stand 10–60 cm high and about 46 cm wide. It is omnivorous and aggressive, forming single-queen and multiple-queen colonies and floating rafts during floods. IUCN has not assessed it; it is ranked among the world's worst invasive alien species.