Texas Invasive Species InstituteSolenopsis richteri
Black Imported Fire Ant (BIFA)
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Photographer: Eli Sarnat
Source: Bugwood.org
Adult Description: Originally this species was thought to be a sub-species of the Red Imported Fire Ant (Solenopsis invicta) but has been described as its own species because of a large difference in range and living habitats of the two imported fire ants. Ants belonging to the genus Solenopsis can readily be distinguished from all other ant species in North America by their 10-segmented antennae with a 2-segmented club. These characteristics, combined with the presence of a sting, a two-segmented pedicel and an unarmed propodeum make identification of the genus relatively easy. Characteristics that differentiate this ant from the RIFA are humeral processes on major worker ants and a large reddish-orange colored spot on the first segment of the gaster.
Ecological Threat: This ant out-competes the native fire ants and hundreds of other species of ants. The two native fire ants, S. geminata and S. xyloni, have not been collected in either MS or AL in many years and it is thought that the two imported fire ants and their hybrid have out-competed them for resources and effectively driven them out of this area. Thankfully, BIFA is less aggressive than the Red Imported Fire Ant so it hasn’t spread as quickly. However, being omnivorous (mostly insectivorous) is still a threat to native ant species, other insect species and has also been observed to have a large impact on the ground nesting animals from insects to reptile, birds and mammals.
Biology: One of the identifying characteristics of a fire ant colony is the earthen nest or mound. The mound is a conically-shaped dome of excavated soil that has a hard, rain-resistant crust. Ants have different castes so there are different types of ant morphologies for one species. There are major workers (pictured above), minor workers, alate males (winged) and the queen ants. All workers are sterile and males are strictly used for reproduction and the colonization of a new ant colony, and once that is done they die. One or more wingless queens can be present in an ant colony it just depends on the size of the colony but they never leave the colony. All foraging and up keeping of the larvae broods are done by the worker ants.
Eggs hatch after 5 to 8 days with the time variance due mainly to caste and sex of the egg. Worker ants then care for the larvae which have four molting periods (instars) and then pupate. When they enter the pupal stage it is moved into storage with the other pupae. Once done young adult ants emerge from the pupae and are soft and pale becoming darker and harder within a couple of days. Colonies mature in two years. In the United States, egg production is seasonal, beginning in March. Sexual broods are laid before worker broods. Egg production ends with the onset of winter. Workers live a little over half a year in the wild, and live anywhere from 10 to 70 weeks in laboratories. Successful queens live approximately five years in the wild, and 6 to 7 years in captivity.
History: Solenopsis richteri, arrived at the port of Mobile, Alabama in 1918, from South America, probably Argentina; as a stowaway within soil used as ballast in cargo ships. Over the past century the BIFA has slowly expanded into surrounding states of Alabama; unlike the RIFA which has expanded as far west as Texas and as far North as Maryland.
U.S. Habitat: The BIFA prefers open area grasslands, predominantly pastures and lawns. The pampas of Argentina was its original preferred habitat. Young BIFA colonies prefer moister areas in which to build their mounds, whereas more mature colonies tend to emigrate to drier soil as they grow larger. Most BIFA colonies are found at lower elevations, but can be found at elevations as high as 12,000 feet in South America.
Distribution
Native Origin: South America; S. Brazil - N. Argentina and Uruguay
U.S. Present: AL, FL, MS, TN, VA
Management
Efforts to eradicate imported fire ants have been deemed virtually impossible by the USDA but management of these voracious insects are crucial to the survival of other native species. BIFA is susceptible to means of physical, chemical and biological control efforts. 3 gallons of boiling hot water poured onto a mound can eliminate almost 60% of the mound. By chemical means there are pesticides that can be bought at local home and garden stores and can be applied to mounds on a local scale but don’t work on a larger scale. Decapitating flies of the genus Pseudacteon have been used in studies for predation against the imported fire ants. The and P. curvatus is a native of Argentina but only attacks the smaller fire ants while P. tricuspis has been observed to attack large to medium sized fire ants. Together the Pseudacteon species complex could help with management of imported fire ants but the flies have to be able to establish themselves. Also, the other drawback of the biological control is the flies that would be used are also invasive but they would have less of the impact that the imported fire ants have. Researchers are also looking into bacteria and viruses that can infect only the imported fire ants that could also be used as biological controls.
Text References
Holldobler, B., E. Wilson. 1994. Journey to the Ants: A Story of Scientific Exploration. Cambridge, MA: Harvard University Press.
Taber, S. 2000. Fire Ants. College Station, TX: Texas A&M University Press.
Williams, D. F., Oi, D. H., Porter, S. D., Pereira, R. M., & Briano, J. A. 2003. Biological control of imported fire ants (Hymenoptera: Formicidae). American Entomologist, 49(3):150-163.
Internet Sources
http://ipmworld.umn.edu/chapters/lockley.htm
http://animaldiversity.ummz.umich.edu/accounts/Solenopsis_richteri/
http://invasive.org/browse/subinfo.cfm?sub=4676
http://www.issg.org/database/species/reference_files/solric/solricmanage.pdf
