Subfamily MYRMICINAE
Tribe SOLENOPSIDINI
Solenopsis invicta X richteri

Introduction
The genus Solenopsis includes both the "fire ants", known for their aggressive nature and potent sting, and the minute "thief ants", many of which are lestobiotic subterranaen or arboreal species that are rarely collected. Many species may be polygynous.

Solenopsis invicta X richteri, is a hybrid between S. invicta(the red imported fire ant) and S. richteri (the black imported fire ant). The hybrid fire ant, along with both S. invicta and S. richteri, is a major agricultural and urban pest throughout the southeastern states that also causes both medical and environmental harm resulting in a cost of many millions of dollars per year for southeastern states.

Identification
Generic level identification of Solenopsis is relatively straight forward, although sizes are greatly variable ranging from approximately 1.0 mm to over 4.0 mm. The genus can be basically characterized by the following: mandible with four teeth (usually), bicarinate clypeus with 0-5 teeth, median part of clypeus with a pair of longitudinal carinae medially or at lateral edges, 10-segmented antennae that terminates in a distinctive 2-segmented club, overall shiny appearance and general lack of or reduced sculpture (when present usually restricted to rugulae or striae on the head, alitrunk, petiole, and postpetiole), lack of propodeal spines or other protuberances on the alitrunk, well developed petiole and postpetiole, and a well developed sting. Workers are either polymorphic (especially in the fire ant group) or monomorphic (especially thief ants).

Hybridization is not uncommon among the larger fire ant group, which can make identification of some species difficult. Identification of thief ants is perhaps even more challenging due to their minute size, similar appearance of workers of one species to another, taxonomic problems, and lack of knowledge of all castes.

Solenopsis invicta X richteri can generally be recognized by their large mounds, polymorphic castes (varying sizes of workers), 10 segmented antennae ending in a 2 segmented club, lack of spines on propodeum, reddish to brownish color, median tooth on the anterior border of the clypeus, and combination of characters of both S. invicta and S. richteri. However, because they are hybrids, they can be a challenge to differentiate from S. invicta and S. richteri. The most reliable method for identification of this group is a cuticular hydrocarbon test, which some labs are now equipped to do.

Biology and Economic Importance
The red impored fire ant, intduced from Argentina or Brazil sometime between 1933 and 1945, together with Solenopsis richteri, the black imported fire ant, introduced sometime near 1918 from South America (probably Argentina), have wreaked havoc on the economy of the South. These two species can mate with one another producing a hybrid, which can in turn prorduce viable offspring. Consequently, there is some question of whether or not S. invicta and S. richteri are truely "good" species.

Distribution
Distributionally, S. invicta is found in the southern halves of both AL and MS and also found in the western portion of MS following the Mississippi River northward (also in several other states), whereas S. richteri tends to be found in the northeastern part of MS and northwestern portions of AL, with the hybrid found in a band between the two populations. This is not a static situation and S. invicta appears to be on a continuous path northward, bounded only by temperature restraints (which it appears to be overcoming). As S. invicta moves northward, so also do the populations of S. richteri and the hybrid.

Literature Cited

Links
Extension Fire Ant Site- http://www.extension.org/fire+ants
Texas A & M Fire Ant Site- http://fireant.tamu.edu/
The Imported Fire Ant and Its Control - http://msucares.com/insects/fireants/index.html
Imported Fire Ants in Tennessee - http://fireants.utk.edu/
Imported Fire Ant and Household Insects (IFAHI) research site-http://www.ars.usda.gov/Main/site_main.htm?modecode=66-15-10-15
LSU red imported fire ant research- http://www.lsu.edu/ants/index.shtml
Control of the Red Imported Fire Ant -http://www.ces.ncsu.edu/depts/ent/notes/Urban/ifa.htm
List of Fire Ant Web Page Links - http://hbs.bishopmuseum.org/ants/Solenopsis/Sollinks.html