Solenopsis geminata - PIAkey factsheet

Threat Level: Medium

Solenopsis geminata 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 and square-shaped heads. Like all myrmicines, S. geminata has a two-segmented waist and a gaster armed with a stinger.

Solenopsis invicta 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. geminata 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 geminata is commonly referred to as the Tropical Red Fire Ant. It is an aggressive species with a painful sting and is known to cause damage to ecological and agricultural systems. For a more complete review of the biology, impacts and management of S. geminata, users are referred to the IUCN/SSC Invasive Species Specialist Group (ISSG) web page. Although S. geminata is an unpleasant ant, it is preferable to S. invicta. If either species is collected during invasive ant surveys, it is highly recommended that specimens from each sample be identified under the microscope to confirm the identity.

	larger worker	smaller worker
Waist with two segments (petiole & postpetiole)
Propodeal spines absent
Antennal scrobe absent
Antennae with 10 segments Antennal club with two segments		(not available)
Eyes large with many facets
Anterior clypeal margin with two lateral teeth, but middle tooth absent (see S. invicta for example of middle tooth present)
Worker caste polymorphic

Solenopsis geminata vs. S. invicta, S. papuana, Monomorium species

	S. geminata	S. invicta	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	absent	present	(not applicable)	(not applicable)
	S. geminata	S. invicta	S. papuana	Monomorium spp.

Solenopsis geminata CASENT0171102 (head, close-up, large worker)	Solenopsis geminata CASENT0171029 (head, small worker)	Solenopsis geminata at sugar bait (units in mm) (Lautoka, Fiji)
Solenopsis geminata CASENT0171102 (head,full face, large worker)		Solenopsis geminata workers at sugar bait (Lautoka, Fiji)
, Solenopsis geminata CASENT0171102 (profile, large worker)	Solenopsis geminata CASENT0171029 (profile, small worker)	Solenopsis geminata workers at sugar bait (Lautoka, Fiji)
Solenopsis geminata CASENT0171102 (dorsal, large worker)	Solenopsis geminata CASENT0171029 (dorsal, small worker)	Solenopsis geminata workers at sugar bait (Lautoka, Fiji)
Solenopsis geminata CASENT0171102 (label, large worker)	Solenopsis geminata CASENT0171029 (label, small worker)

Solenopsis geminata at peanut butter bait (Lautoka, Fiji). There is also several individuals of Paratrechina vaga which are smaller and darker. Notice the different sizes of the S. geminata. In the field, it is nearly impossible to accurately distinguish between S. geminata & S. invicta.

Solenopsis geminata at cotton ball and sugar solution bait (Lautoka, Fiji). There is also a single individual of Paratrechina vaga which is smaller and darker.

Subfamily Myrmicinae

Solenopsis geminata. Atta geminata Fabricius, 1804: 423 (q.) CENTRAL AMERICA. Roger, 1862c: 289 (w.m.); Mayr, 1867a: 110 (w.q.m.); Wheeler, W.M. 1900b: 21 (l.); Wheeler, G.C. & Wheeler, J. 1955c: 132 (l.); Crozier, 1970: 116 (k.). Combination in Solenopsis: Mayr, 1863: 453. Senior synonym of clypeata, mandibularis: Roger, 1862c: 289; of cephalotes, paleata: Roger, 1863b: 32; Trager, 1991: 163; of glaber, laboriosus, polita: Mayr, 1863: 453; Mayr, 1886c: 362; Trager, 1991: 163; of drewseni: Mayr, 1870b: 996 (footnote); Mayr, 1886d: 460; of coloradensis: Mayr, 1886c: 365; of lincecumii, saxicola: Emery, 1895c: 276; of innota: Wheeler, W.M. 1922a: 877; of nigra: Creighton, 1930b: 59; of laevissima, mellea: Donisthorpe, 1932c: 463, 455 respectively; of rufa (and its junior synonym diabola): Ettershank, 1966: 141; of eduardi (and its junior synonym perversa), medusa (and its junior synonym bahiaensis), galapageia: Trager, 1991: 163. See also: Smith, D.R. 1979: 1386. Current subspecies: nominal plus micans.

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.
Wilson, E.O. & Taylor, R.W. (1967) The ants of Polynesia (Hymenoptera: Formicidae). Pacific Insects Monograph, 14, 1-109.