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Solenopsis picta Emery

Solenopsis picta, full face view of a worker (click image to enlarge).
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Solenopsis picta, side view of a worker (click image to enlarge).
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Solenopsis picta, side view of a queen (click image to enlarge).
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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 picta are small, brownish colored, arboreal nesting species that appear to be confined to the Southeast.

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). The thief ant group shares these characteristics, but workers are minute (usually under 2.0 mm in total length), usually have minute eyes (usually with only 1-5 ommatidia (rarely more than 18, except for S. globularia in our region), minor funicular segments 2-3 typically wider than long (usually longer than wide in the fire ant group).

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.

Worker: SIze, minute (1.3 to 1.45 mm in total length). Coloration: concolorus brown to bicolored with a head reddish brown to darker brown, alitrunk reddish brown, and gaster dark brown; appendages yellowish brown to reddish brown. The eyes are small with 4-5 facets and almond shaped. A well developed metanotal suture is present. The node of petiole is placed anterior to the petiolar-postpetiolar juncture giving the petiole a distinct slender posterior peduncle.

Female: SIze, small (about 3:24 mm in total length), slender, concolorous golden brown to darker brown. Head longer than wide, with fine punctures, angulate lateral clypeal teeth and lacking extralateral teeth. Pronotum finely puncture, with smooth, shiny sculpture; mesopleuron smooth, shiny; and metapleuron with horizontal striae. Petiole wider than postpetiole (in lateral view); petiolar node somewhat triangular and rounded; postpetiolar node oval and globose; and petiole and postpetiole lacking ventral tooth or flange (female description from Pacheco 2007).

Male: Unknown?

This species is one of the few thief ants that is unlikely to be confused with other species in the Southeast. The only other brown colored species are S. nickersoni and S. truncorum. Solenopsis nickersoni has only been reported from Florida and is thought to be a subterranean nesting species. Workers are smaller (about 1.2 mm TL), have pale yellow appendages and do not have the appearance of having a posterior petiolar peduncle. Queens are reddish brown and larger than queens of S. picta. Solenopsis truncorum is also only known from Florida. Workers are reddish brown and much larger in size than picta.

Biology and Economic Importance
This species nests in dead wood, hollow twigs, branches, and galls in pines and hardwoods such as Carya sp. (pecan) and Quercus sp. Antweb gives data for this species having been collected in longleaf pine adn in a cynipid gall on Quercus phellos.

I collected a series of workers at peanut butter bait on Quercus nigra. Hundreds of workers were present, although the nest location was not located. Members of the MEM have collected this species in a variety of habitats including bogs, mixed pine/hardwood forests, open maritime forests along the Mississippi Gulf Coast, steep sloped upland forests, and bottomland hardwood forests.

AL, FL, GA, LA, MS, NC, SC, TN, and TX.

Literature Cited
Pacheco, J. A. 2007. The New World ants of the genus Solenopsis (Hymenoptera: Formicidae). PhD dissertation, The University of Texas at El Paso. i-xxi +543 pp.


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