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Fire Ants (Solenopsis invicta)

Detailing the physical features, habits, territorial reach and other identifying qualities of the Fire Ants

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The most notorious of Fire Ants, Red Imported Fire Ants are a pain in every possibly way, and they are proving difficult to get rid of.

Updated: 01/03/2022; Authored By Staff Writer; Content ©www.InsectIdentification.org
Introduced into the U.S. after the Great Depression, the Red Imported Fire Ant (RIFA) is now established in southern U.S. states and Mexico. Originally from South America, this species is known for its intensely aggressive defense of its colony by immediately swarming a threat en masse, holding on to it by biting it, and then stinging it. The stinger at the tip of the abdomen injects a chemical that produces a sensation akin to being burned by fire. A severe, lethal, allergic reaction to the ant?s venom is a concern for a small number of victims, but RIFA stings rarely cause death according to the National Institute of Health (American Journal of Forensic Medicine and Pathology: June 1998). Sting sites develop into white, pimple-like pustules that do eventually heal. Itching and possible infection at the sites may develop after the pustules diminish.

Red Imported Fire Ants come in various sizes, unlike many other types of ants with uniform size. Some are much larger than others. Male swarmers are black. The queen and workers have a coppery red head and thorax, but a black rear end (abdomen). A Red Imported Fire Ant colony is built in the ground. Sometimes workers may be seen in trees, but nests are not established there. Many colonies are hidden under logs or debris, but in open areas that lack cover like farms, campgrounds, and playgrounds, soft, earthy mounds are created in plain sight. These more visible mounds can be anywhere from 7 cm to 1 m (3 inches to 3 feet) tall and are usually under 45 cm (18 inches) in diameter. RIFA prefer moist areas, so colonies are often found near water sources. (Floods and heavy rains often bring out the ants, and clusters of them form ?rafts? that can float on water until solid ground is reached.) Large and small individual ants from the colony may be active on and around the mound, but many people and pets unwittingly step on mounds that do not have obvious signs of life. Unlike other ants, RIFA mounds do not have a central opening hole, so they are less likely to be quickly identified as an ant colony. People and children living in areas where RIFA exist should avoid compressing mounded soil with their feet in order push it back into the lawn. Any object that disturbs the mound causes a frenzy of biting and stinging ants to crawl straight up the object, be it a foot, paw, pencil, or wooden stake. Fleeing from the ant nest area as quickly as possible, despite the painful biting and stinging, minimizes the number of ants that attack.

This species of ant eats anything and everything. Plant matter, carrion, and even living animals are all food sources for the colony. It is common to see dead insects, rodents, and even large animal carcasses covered in ants. Red Imported Fire Ants use their numbers and venom to overwhelm living animals as well. Lizards, birds, rodents, and toads have been overwhelmed by the onslaught and killed.

There are many areas of research dedicated to controlling and hopefully eradicating the Red Imported Fire Ant from its non-native countries. Universities, state agencies, and the federal government have spent millions of dollars trying to find ways to reduce and eliminate RIFA. One area of biologic control involves the natural enemy of the ant, a parasitic Phorid Fly. The fly lays its egg on the ant and the fly larva feeds on its tissues, eventually killing the ant by causing the connection between the ant?s head and body to dissolve. This type of fly has been introduced to Texas and Alabama to try to curb the growth of the ant population. Other types of native fire ants have been found to seek out and kill the RIFA queen in a new nest while she is unguarded. A fungus and protozoan are also being studied for their ability to manage Red Imported Fire Ants. Broadcasting chemical insecticides like poisonous fire ant bait, dust, and granules are effective at killing a colony, though it may take weeks to work completely. Extermination efforts using chemicals directly on a mound have also been employed, but do not always kill the queen, which usually results in a reestablished population. Despite claims, grits are ineffective at killing them. Though single mounds can be exterminated, often a new population moves into the same the area within years, so the battle to eliminate RIFA from lawns, parks, and fields should be considered an on-going effort. Cold winters and drought conditions seem to hinder the spread of RIFA into northern and western states, but mild winters and irrigation may aid their migration into those regions. No state has eradicated RIFA yet, so unfortunately, this problematic species is likely to persist in North America for much longer than anyone wants.©InsectIdentification.org

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General Characteristics

Capability, Shape, Texture/Pattern, Benefits, Dangers
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Taxonomic Hierarchy

Species Breakdown
Kingdom: Animalia
  Phylum: Arthropoda
    Class: Insecta
      Order: Hymenoptera
        Family: Formicidae
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          Genus: Solenopsis
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            Species: invicta

Identifying Information

Size, Colors, Features
Scientific Name: Solenopsis invicta
Other Name(s): Red Imported Fire Ant (RIFA)
Category: Bee, Ant, Wasp and Similar
Size (Adult; Length): 2mm to 6mm (0.07" to 0.23")
Colorwheel Graphic Colors: red; brown; black
Descriptors: black butt or rear end; stinging; biting; painful; dangerous; harmful; bent antennae; group; cluster; mound; red head and middle

Relative Size Comparison

Typical Size Between 2mm (0.1in) and 6mm (0.2in)
Lo: 2mm
Md: 4mm
Hi: 6mm

Territorial Map*

U.S., Canada, and Mexico
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Prince Edward Is.  
* MAP NOTES: The territorial heat map above showcases (in red) the states and territories of North America where the Fire Ants may be found (but is not limited to). This sort of data is useful when attempting to see concentrations of particular species across the continent as well as revealing possible migratory patterns over a species' given lifespan. Some insects are naturally confined by environment, weather, mating habits, food resources and the like while others see widespread expansion across most, or all, of North America. States/Territories shown above are a general indicator of areas inhabited by the Fire Ants. Insects generally go where they please, typically driven by diet, environmental changes, and / or mating habits.
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