Key to species of Paratrechina in the southeastern United States

(from Trager 1984)

There are a couple of undescribed species in this group that may be parasitic on other Paratrechina species.  These species do apparently do not have a worker caste and the males are unusual in that they have characteristics of both males and workers.  These undescribed species are not included in the key.

 For explanations of measurements and indices see "How to Use the Keys".

1 

Scapes and legs very long (SI > 165, FI >115); color weakly shining black or gray with bluish reflections; pubescence sparse, short, and barely visible (usually associated with human dwellings and urban areas)
...longicornis (Latreille) (subgenus Paratrechina)
  Scapes and legs not unusally long (SI < 130, FI < 105); color varies, but never with blueish reflections; shiny or dull, if dull, then due to dense pubescence
..2 (subgenus Nylanderia)
2 (1)   Color yellow to pale whitish; nests are found in sandy soil or sand dunes and are surrounded by a conspicuous crater in clearings between vegetation
....3
  Color uniformly dark colored or bicolored; usually nest in more mesic habitats (except parvula which may be in sandy areas, but color not uniformly yellow) and usually nests are more inconspicuous being found under moss, rocks, logs, litter, etc. or near man-made structures
...4
3(2)  Color yellow with the gaster being infuscated posteriorly; macrochaetae (macrochaetae are large, free standing setae with barbs) on thorax are flexuous and dark brown (obviously darker than body color); scapes have 5-17 (usually 7-12) macrochaetae and suberect pubescence (sandy areas)
  Color yellow or whitish and gaster only slightly darker at most; the thoracic pilosity is nearly straight and about the same color as body or only slightly darker; scapes have 0-4 (usually 1-3) standing macrochaetae and pubescence is short and appressed (coastal, dunes)
4(2)  Scapes with 4 or less macrochaetae
...5
  Scapes with 4 or more macrochaetae, usually with at least 7
...6
5(4)  Usually bicolored, thorax yellowish to reddish-brown, head and gaster darker, and with the middle and hind coxae pale (much lighter than the fore coxae or the rest of the legs); scapes with 1-4 macrochaetae; the eyes either reach the sides of head or only fail to do so by 1-2 facet widths (in full face view); size small (HL generally 0.51-0.57) (FL, Gulf Coast)
  Usually uniform dark brown (at most weakly bicolored or some populations lighter in color); the appendages are somewhat lighter or yellowish, but the middle and hind coxae usually are not contrastingly pale compared with the fore coxae; scapes always lack macrochaetae; the eyes fail to reach the sides of head by about 1/4 of their width (in full face view); size larger (Hl >0.60)
6(4)  The thorax and gaster covered with pubescence, except in some cases where it is only lacking on the pleura and pronotal disc, giving a dull appearance
....7
  The thorax and gaster with pubescence greatly reduced, appearance shiny
....9
7(6) Uniform dark brown or black; macrochaetae on alitrunk thick, nearly straight, relatively short and abundant; entire body pubescent, head in frontal view with dense pubescence; size large (HL about 0.70 - 0.81 mm); eye large, OI 26-30; ocelli present
  Color reddish-brown, yellowish-brown, to dark brown; macrochaetae longer, more flexuous; head in frontal view with scattered pubescence, appearing shiny, side of pronotum with or without dense pubesence; size large or smaller; eye smaller, OI 23-26
8
8(7)    Color of body light reddish-brown; pronotal disk and sides of pronotum with dense pubescence; size large (HL 0.77-0.85 mm) ( FL and TX)
  Yellowish brown to dark brown with middle and hind coxae distinctly lighter; pronotal disk and sometimes side of pronotum glabrous and shining; size smaller (HL usually 0.56 - 0.66 mm) (only known from FL)
9(6) Color a uniform dark brown with the appendages only somewhat lighter; a dense row of longitudinally aligned pubescence found on the anterior edge of the propodeum (caution: some workers of P. vividula also have similar pubescense); the front of pronotum and the mesonotum with at least some dilute pubescence; the head with shallow pubigrous punctures and dense pubescence that is mostly aligned with the long axis of the head (found in FL, AL, GA, and the Carolinas, in marshes, diches, damp pastures, swamp edges, rotten wood, cow dung, or tussocks)
  The middle and hind coxae and/or the thorax and legs are lighter than the gaster and the head; promesonotum with pubescence either lacking or very sparse, propodeum often lacking pubescence as well; the head smooth and shining or weakly and irregularly punctate beneath pubescence; the pubescence on head may or may not be dilute and is not parallel to the long axis of the head (usually not found in marshes or poorly drained pastures)
...10
10(9)  The pubescence on head is dilute, in the preoccipital area most of the spaces between the setae (not the macrochaetae, but the simple setae) are as wide as the length of the setae or wider; the anterior 1/2 of the head (except sometimes the frons) lacking pubescence
...11
  The pubescence of head is denser, in the preoccipital area most of the spaces between setae are no wider than the length of the setae and usually less (common in mesic woods)
11(10) Eye about 1/4 HL or even slightly larger, OI 24-47 (old fields, cultivated areas, gardens, disturbed areas, etc.)
 

Eye smaller, OI usually 20-24 (possible, mostly more western but found in AK, TN, under stones, moss clumps, or bark in forest openings and other open or disturbed places)
Note:  P. brusii (Wheeler) was recorded by M. R. Smith as occurring in MS, but according to Trager it is western.  Also, there is a specimen identified as P. fulva (Mayr) in the MEM collection from MS, but it the id is questionable as it is generally a more tropical species.  It is within the realm of possiblity that it could be found as an introduction, but it is not an established resident by any means.