Practical information to identify and manage non-native, invasive plants and animals
The Quiet Invasion:
A Guide to Invasive Species of the Galveston Bay Area
Red imported fire ant; RIFA
Solenopsis invicta

ITIS TSN:154239
Presence:Current Invaders
Habitat:Terrestrial
Native Range:South America
Human Health
RIFA have a venomous sting that improves their ability to capture large prey (Holway et al. 2002; ISSG 2009e). They are aggressive and will attack humans, pets and livestock. RIFA bite their prey in a grasping motion and then inject an alkaloid venom called Solenopsin from a stinger located on the abdomen. It is the injection of the venom that results in the painful sting commonly associated with this species. A RIFA sting will result in immediately painful, itchy red welts which may turn in small blisters over time. Those allergic to fire ant venom may also experience difficulty breathing, rapid heart rate, and throat swelling (Heller 2009).
Prohibited Lists
As of 2010, much of Texas is included in the quarantine area for this species. The U.S. Department of Agriculture (USDA) along with some state governments have established quarantine areas to prohibit the movement of items such as nursery stock and soil-moving equipment out of states where RIFA is known to exist (see geographic distribution below) (USDA 2010).
Introduction Pathways
RIFA was introduced into the U.S. from South America at the port of Mobile, Alabama in the late 1930's. The species likely came to the port in soil used as ballast in cargo ships (USDA 2010). S. invicta may also be introduced via the movement of agricultural/aquacultural material and equipment, and nursery and landscaping materials (potted plants, soil, and mulch) (ISSG 2009e). Locally, the RIFA infestation reached the upper Texas coast in the early 1970's (Glass and Roach 1997).
Geographic Distribution
S. invicta is found in Alabama, Arkansas, California, Florida, Georgia, Louisiana, Mississippi, New Mexico, North Carolina, Oklahoma, South Carolina, Tennessee, Texas, and Puerto Rico (NAPIS 2010). RIFA is found in all counties of the Lower Galveston Bay watershed as well as nearly every county in Texas with the exception of a few counties in the Texas Panhandle.
Specific Primary Habitats
Red imported fire ants are found in many areas including coastal habitats, deserts, forests, croplands, pastures, grasslands, riparian zones, scrub/shrub lands, and suburban/urban areas.
Ecological, Economic, or Social Impact
S. invicta often dominate due to their aggressive foraging behavior, high reproductive capability, lack of predators and strong competitors (Allen et al. 2004). RIFA compete with native ant species and prey on other animals including reptiles, amphibians, birds, and small mammals. Locally, RIFA predate on colonial waterbird eggs and nestlings on bay rookery islands with higher elevations (Glass and Roach 1997). S. invicta cause major economic losses and public health nuisances. They are documented as damaging agricultural commodities (crops and livestock) and electrical equipment. Economic losses and costs to control this invasive species are estimated to be $1 billion annually in the U.S. ($300 million per year in Texas). Additionally, two people were reportedly killed by fire ants in Mississippi in 2002 (Pimentel et al. 2005).
Physical Description
RIFA are small, varying from 2 to 6 mm in length, and are reddish-brown in color. Nests are found in open areas, but mounds may not be evident (ISSG 2009e). Distinguishing between imported and native fire ant species is difficult. However, the native fire ant (S. geminata) can be distinguished from S. invicta. The heads of the largest S. geminata workers are wider than their abdominal segments.
Reproduction Characteristics
The queen produces 800 to 2,000 eggs per day. She produces sterile worker females and occasionally fertile females and males. Fertilized females may start new colonies by leaving the nest with a cohort of workers and larvae (ISSG 2009e).
Feeding
RIFA feed on invertebrates, vertebrates, plants, and oily or sugary foods. However the species is known to prefer protein-rich food sources (ISSG 2009e).
Control
RIFA are commonly controlled with high-protein content insecticidal baits applied in a targeted manner. When using any chemical to control pests great care should be exercised to limit exposure of humans and the environment to potentially dangerous chemicals.

This species belongs to the following lists:
Images
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Mound of the red imported fire ant (<i>S. invicta</i>). Photo courtesy USDA APHIS PPQ Archive, Bugwood.org.
Mound of the red imported fire ant (S. invicta). Photo courtesy USDA APHIS PPQ Archive, Bugwood.org.
Mound of the red imported fire ant (<i>S. invicta</i>) with adults and pupae visible. Photo courtesy Chris Evans, River to River CWMA, Bugwood.org.
Mound of the red imported fire ant (S. invicta) with adults and pupae visible. Photo courtesy Chris Evans, River to River CWMA, Bugwood.org.
Closeup of abdomen and stinger of the red imported fire ant (<i>S. invicta</i>). Photo courtesy Pest and Diseases Image Library, Bugwood.org.
Closeup of abdomen and stinger of the red imported fire ant (S. invicta). Photo courtesy Pest and Diseases Image Library, Bugwood.org.
Closeup of head of the red imported fire ant (<i>S. invicta</i>). Photo courtesy USDA APHIS PPQ Archive, Bugwood.org.
Closeup of head of the red imported fire ant (S. invicta). Photo courtesy USDA APHIS PPQ Archive, Bugwood.org.
Page Updated/Reviewed: 07/14/2010 1:39 PM
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