Key to species of Nylanderia in the southeastern United States

(from Trager 1984 and Kallal and LaPolla 2012)

*A recent revision by LaPolla et al. (2010) elevated the subgenus Nylanderia to generic level, and in 2012, Kallal and Lapolla (2012) revived the genus for the Nearctic region.

There are several undescribed species in this group, a couple of which may be parasitic on other Nylanderia species.  These species 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, but will be added after they are described.

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

1 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
...2
  The thorax and gaster with pubescence greatly reduced, appearance shiny
...5
2(1) Uniform dark brown to almost black; macrochaetae on mesosoma 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 or yellowish-brown; macrochaetae longer, more flexuous; head in frontal view with scattered pubescence, appearing shiny, side of pronotum with or without dense pubescence; size large or smaller; eye smaller, OI 23-26
...3
3(2) 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)  
  Color of body light reddish-brown; pronotal disk and sides of pronotum with dense pubescence; size large (HL 0.77-0.85 mm) (FL, LA, MS, and TX)  
...4
Note: N. fulva and N. pubens worker are extremely difficult, if not impossible to separate using morphological methods. The most reliable way to separate the following two species (fulva and pubens) is comparing differences in the genitalia of the males.
4(3)    Workers smaller on average (TL 2.0-2.5 mm); posterior border of head straight or only weakly emarginate; head with dense pubenscence. Parameres of male genitalia with sparse pilosity of uneven length and orientation; supercolonial, extremely large populations, found in FL, southern LA and MS, and eastern TX
  Workers larger on average (TL 2.75-3.0 mm); posterior border of head emarginate; head with sparse pubenscence. Paramere of the male genitalia bordered by a dense fringe of at least 30 blondish macrochaetae; outdoor populations in the US restricted to southern FL
5(1) Scape with 4 or less macrochaetae
...6
  Scape with over 5 macrochaetae
...9
6(5) Scape with 0-4 macrochaetae (if 0, then body and macrochaetae pale yellow to white)  
...7
  Scape lacking macrochaetae  
...8
7(6) Color pale yellow to whitish with gaster sometimes slightly darker; thoracic pilosity nearly straight and about the same color as body or only slightly darker; scapes with 0-4 (usually 1-3) standing macrochaetae and pubescence short and appressed; only found in deep sand dunes (MS, AL, GA, and FL)
  Usually bicolored, thorax yellowish to reddish-brown, head and gaster darker, and with middle and hind coxae pale (much lighter than fore coxae or other leg segments); scapes with 1-4 macrochaetae (HL generally 0.51-0.57) (FL, Gulf Coast)
8(6) Overall coloration dark brown, scapes yellow and contrasting with head color
  Overall coloration yellow, scapes also yellow, not contrasting with head color
9(5) Mesosoma, antennae, and legs yellowish; 3 ocelli present; first gastral tergite yellowish and contrasting to the rest of the gaster, which is darker (introduced species, not yet recorded from the SE, but known from Maryland and farther north)
  Color variable; ocelli present or lacking; gaster uniformly colored
...10
10(9) Color predominately yellow; cepahlic pubescense moderate to dense
...11
  Color darker, yellowish-brown to dark brown; cephalic pubescense lacking to dense  
...12
11(10) Gaster brownish distally; gastral macrochaetae abundant; usually found in sandy habitats, but also prairies  
  Gaster uniformly yellow; gastral macrochaetae less abundant; found in forested habitats  
12(10) Coloration brown to dark brown except mesocoxae and metacoxae, which are contrastingly pale compared to the mesosoma in fully developed workers (newly emerged workers are much lighter with body color similar to the color of meso- and metacoxae and can be confused with N. vividula); cephalic pubescence fine, moderate to dense; pubescense lacking on side of propodeum
  Coloration yellowish-brown to brown, all coxae usually colored similarly to body color, but if lighter, then cephalic pubescence sparse and with pubescence on propodeum; cephalic pubescence lacking to dense; propodeum usually at least scattered pubescence  
...13
13(12) 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 pubigerous punctures and dense pubescence (FL, AL, GA, and the Carolinas, in marshes, ditches, damp pastures, swamp edges, rotten wood, cow dung, or tussocks)  
  Yellowish-brown to brown; cephalic pubescence sparse, in the preoccipital area most of the spaces between the 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
...14
14(13) Head somewhat square-shaped with margins of head subparallel (in full face view); eye about 1/4 HL or even slightly larger, OI 24-47 (old fields, cultivated areas, gardens, disturbed areas, etc., widespread in Southeast)
 

Head wth convex lateral margins in full face view; eye smaller, OI usually 20-24 (possible, mostly more western but found in AK, LA, TN, under stones, moss clumps, or bark in forest openings and other open or disturbed places)

Note:  N. bruesii (Wheeler) was recorded by M. R. Smith as occurring in MS, but according to Trager it is western. It is not included in this key.

References

Kallal, R. J. and J. S. LaPolla. 2012. Monograph of Nylanderia (Hymenoptera: Formicidae) of the World, Part II: Nylanderia in the Nearctic. Zootaxa 3508: 1-64.

Lapolla, J. S., S. G. Brady, and S. O. Shattuck. 2010. Phylogeny and taxonomy of the Prenolepis genus-group of ants (Hymenoptera:  Formicidae).  Systematic Entomology 35: 118-131.

Trager, J. C. 1984.  A revision of the genus Paratrechina (Hymenoptera: Formicidae) of the continental United States. Sociobiology 9:  49-162.