Three species of fire ants inhabit the desert southwest: the Solenopsis xyloni, the Solenopsis aurea and the Solenopsis amblychila. The common name refers to the ants’ notoriously nasty sting. “Solenopsis” comes from the Greek solen (channel or pipe) and opsis (appearance, face). “Aurea” refers to that particular species’ golden coloring. In Spanish, fire ants are known as hormiga colorada (red ant) or hormiga brava (surly ant). In Portuguese, they are called formiga de fogo (fire ant), formiga lava-pé (wash foot ant) and formiga toicinheira (lard ant). Amblychila means blunt-lip, (Ambl (o,y) Greek for dull, blunt and Chilo = lip) in reference to the toothless clypeus (a mouthpart), and xyloni means of-wood. This one confuses scientists because the form is not good Greek and the meaning doesn’t really fit the habitat, either.
All three species look similar in shape, color and size. Fire ant workers come in two sizes. Minor workers may be as small as 1/10 inch in length. Major workers may measure up to 1/3 inch. Queens are slightly larger than the biggest workers. The S. xyloni generally has a yellowish-red head and a thorax with a black abdomen, known as the gaster. They may also be completely orangish-red or brownish black. California desert species are the reddest. Of the three species, S. xyloni most closely resembles the notorious red imported fire ant, S. invicta, an invasive species which has infested the entire Southeast. S. aurea is more yellowish than the two other species.
S. xyloni has the widest distribution of the three species, occuring across the southern United States from the Carolinas to Georgia through lowland Tennessee and south-central Kansas to California. S. amblychila has been found in Ramsey Canyon, Arizona, in west Texas, and in the Dona Ana Mountains of southern New Mexico at elevations from 5000 to 8250 feet. S. aurea occurs from Texas to California at elevations below 6600 feet.
Predator and Prey
Fire ants are scavenger-predators that prefer oily or fatty meats and seeds. The menu includes insects, vertebrate carrion and fruits. The ants also harvest seeds and obtain nectar from a variety of plants, including many species of cactus. One early naturalist wrote how “not even clothes are immune from these ant rogues [and] these insect villains [will consume] walnuts, almonds, tomatoes, watermelons, and other fruits and vegetables.”
Fire ants are an aggressive species and when a good food source is found, fire ant workers will displace other ant species. They generally accomplish this through a process known as “gaster wagging” or “flagging,” where a worker will produce an aerosolized drop of venom on her hind end and disperse the poison toward or onto the enemy.
The Argentine ant (Iridomyrmex humilis) will attack and annihilate fire ant colonies, according to the early naturalist who viewed the insects as rogues and villains.
Habits and Habitat
Large colonies of fire ants nest in the soil, often near moist areas, such as river banks, pond edges, watered lawns and highway edges. A single nest, usually less than _ square yard, may have several small openings on the surface or in fissures; no opening is central. The ants shift the entrance during the season and may transport immature ants between openings. Excavated soil is often an irregular and variably shaped mound of loose soil, but it can also form a crater.
Near homes, they may nest at the edge of walks, in cracks in the cement, or adjacent to steps. Inside homes, nests are built in the walls, in the vicinity of kitchens. The ants forage at night, with mostly the smaller workers seeking out food. Larger workers spend little time away from the nest, but they come to the surface quickly when disturbed.
Nuptial flights, when males and queens seek out mates and new nests, occur in the afternoon following a rain storm, from May through September. Colonies are founded by small groups of queens or single queens. Only one queen survives, and within a year or so, the colony expands into thousands of individuals.
Fire ants are well known for their propensity to “boil out of the ground” when their nest is disturbed. They will sting and bite the intruder, causing memorably unpleasant pain.