Threat Level: High

Solenopsis invicta is a medium-sized reddish species with 10-segmented antennae, two-segmented antennal clubs, no antennal scrobes, no propodeal spines, unsculptured heads and bodies, abundant thin and erect pilosity, and a polymorphic worker caste. The largest workers have disproportionately large heads. Like all myrmicines, S. invicta has a two-segmented waist and a gaster armed with a stinger.

Solenopsis geminata is easily confused with S. geminata. The workers of both species overlap strongly in color, size and shape, and are impossible to differentiate in the field. The most reliable character for separating the two is the absence or presence of a middle tooth on the anterior clypeal margin. The middle tooth is present in S. invicta and absent in S. geminata.

Solenopsis papuana is easily distinguishable from S. invicta by its minute size, minute eyes and monomorphic worker caste.

Monomorium can sometimes be mistaken for Solenopsis because both genera lack propodeal spines. However, the PIAkey Monomorium all have 12-segmented antennae with three-segmented antennal clubs, and PIAkey Solenopsis all have 10-segmented antennae with two-segmented antennal clubs.

Solenopsis invicta, commonly known as the Red Imported Fire Ant (RIFA), is the most well studied and notorious ant in the world. The extensive damage caused to ecological and agricultural systems by S. invicta is well documented, and the multiple painful stings caused by multiple attacks can cause allergic reactions to humans. Solenopsis invicta is considered by the IUCN/SSC Invasive Species Specialist Group (ISSG) to be one of the world's worst 100 invasive species. Recent introductions of S. invicta into China, Australia and New Zealand are evidence of the potential for the species to spread throughout the Pacific Island area.

If a specimen collected from an uninfected region is identified as S. invicta it is recommended that the sample be sent to a taxonomic specialist for confirmation. If confirmed, it is recommended that an emergency eradication or management plan be initiated as quickly as possible.

		large worker	smaller worker
Waist with two segments (petiole & postpetiole)
Propodeal spines absent
Antennal scrobe absent
Antennae with a total of ten segments Antennal club with two segments
Eyes large with many facets
Anterior clypeal margin with middle tooth between two lateral teeth (compare with S. geminata)
Worker caste polymorphic

	S. invicta	S. geminata	S. papuana	Monomorium spp.
Head
Profile
Antennae segments (total)	10	10	10	12
Number of antennal club segments	two	two	two	three
Eyes	large with many facets	large with many facets	small with few facets	(not applicable)
Worker caste	polymorphic (workers of different sizes)	polymorphic (workers of different sizes)	monomorphic (workers all of same size)	(not applicable)
Size	Moderate (>2mm)	Moderate (>2mm)	Small (<2mm)	(not applicable)
Anterior clypeal margin with middle tooth	present	absent	(not applicable)	(not applicable)
	S. invicta	S. geminata	S. papuana	Monomorium spp.

• Antweb: specimen images, data & maps
  
  
• Global Invasive Species Database: information about ecology, distribution, impacts, management, references, links and contacts
  
  
• Bolton, B. (1995) A new general catalogue of the ants of the world. Harvard University Press, Cambridge, Massachusetts, 504 pp.