This is a draft key for workers of South American species of Pogonomyrmex

that lack striae on their first gastral tergum. Note that species in the

brevibarbis-group lack these striae, but this group will be treated in a

separate manuscript. Please send comments or edits to RAJ so as to increase

accuracy and utility of the key. Note that several species are keyed out

twice (denoted by [part]) because they exhibit intraspecific variation with

respect to striae on their first gastral tergum, i.e, individuals lack striae

or individuals with striae that extend well beyond the base of the first

gastral tergum – such variation can occur within colonies. Only individuals

lacking these striae are treated herein.

Species names given in apostrophes (“ “) represent unpublished manuscript

names (status changes and undescribed species) that are not to be used until

this monograph is formally published. The couplet for each species is

linked to a web page for that species with taxonomic history, descriptions,

photos, and other information.

Pogonomyrmex of South America; key to species based on the worker caste

1 Fine, dense, incised striae (usually longitudinal) cover anterior

one-third to all of first gastral tergum ----------------- *** (see below)

-- Fine, dense, incised striae lacking or restricted to base of first gastral

tergum ----------------------------------------------------------------- 2

2 Head with scattered small foveae; in full-face view, part to all of

cephalic dorsum with fine longitudinal striae; antennal scapes short,

extending less than one-third the distance from posterior margin of eye

to posterior corner of head (coarctatus-group) ------------------------- 3

-- Head lacking foveae; in full-face view, cephalic dorsum with prominent

longitudinal rugae or rugoreticulate; antennal scapes longer, extending

more than one-half the distance from posterior margin of eye to posterior

corner of head --------------------------------------------------------- 6

3 Striae cover most of cephalic dorsum, areas lacking striae shining to

strongly shining ------------------------------------------------------ 4

-- Striae cover entire cephalic dorsum, entire dorsum weakly shining ----- 5

4 Workers usually larger, strongly polymorphic with supermajors

(HW = 1.94-3.54); weak to moderately coarse rugae on posterior surface of

petiole; rugae on dorsum of postpetiole absent or weak, if present usually

restricted to posterior margin; inferior propodeal spines lacking or

very reduced in size, broadly rounded; interrugal spaces on mesosoma

granulate, weakly shining ------------------------------------- coarctatus

-- Workers smaller, monomorphic (HW = 1.91-2.33); coarse rugae on posterior

surface of petiole; weak to moderately coarse rugae on dorsum of

postpetiole; inferior propodeal spines pronounced, wider than long, apex

bluntly angulate to acuminate; interrugal spaces on mesosoma smooth,

strongly shining ------------------------------------------------- marcusi

5 In profile, lateral lobe of clypeus massively enlarged with narrow

gap (much less than width of antennal scape) between clypeal lobe and

frontal carina; concolorous ferruginous orange to orange-red ---- lobatus

-- In profile, lateral lobe of clypeus not enlarged with broad gap (similar

to width of antennal scape) between clypeal lobe and frontal carina;

bicolored, head dark red to reddish-black, gaster blackish -------- micans

6 In frontal view, head elongate (CI < 90); hind femur long, HFI > 120;

entire scape strongly striate; psammophore poorly-developed, consisting of

hairs scattered over ventral side of head (cunicularius-group) --------- 7

-- In frontal view, head subquadrate to quadrate (CI > 90); hind femur rarely

long, HFI rarely > 100; scape smooth to moderately striate; psammophore

poorly to well-developed ----------------------------------------------- 9

7 In profile, node of petiole rounded; inferior propodeal spines wider than

high, broadly rounded; first gastral tergum smooth and polished,

strongly shining; superior propodeal spines shorter than distance between

bases ------------------------------------------------------- cunicularius

-- In profile, node of petiole angulate; inferior propodeal spines about as

wide as high, acuminate; first gastral tergum moderately to strongly

coriarious, dull to weakly shining; superior propodeal spines longer than

distance between bases ------------------------------------------------- 8

8 Sculpturing on dorsum of mesosoma and posterior surface of petiole coarse,

rugoreticulate to vermiculate; bicolored, mesosoma and petiole medium

to dark orangish-brown to reddish-brown, rest of body lighter - “serpens”

-- Sculpturing on dorsum of mesosoma and posterior surface of petiole weak

to moderately coarse, rugae irregular to weakly rugoreticulate;

body concolorous tannish-red ------------------------------ “pencosensis”

9 Superior propodeal spines absent or consisting of small to moderate sized

denticles or tubercles ------------------------------------------------ 10

-- Superior propodeal spines present, moderately to well developed ------- 11

10 Dorsum of postpetiole with regular to wavy transverse rugae ---- theresiae

-- Dorsum of postpetiole lacking transverse rugae ------------------- inermis

11 Superior and inferior propodeal spines long, acuminate; in profile,

posterior surface of petiole with crest along anterior margin;

anteroventral margin of peduncle with acuminate spine; mesosoma with at

least several long flexuous hairs; anterior margin of clypeus with minute

medial tooth (sylvestris-group) --------------------------------------- 12

-- Superior and inferior propodeal spines rarely long and acuminate; in

profile, posterior face of petiole rarely with crest along anterior

margin; anteroventral margin of peduncle straight or with triangular

process, but lacking acuminate spine; mesosoma rarely with long flexuous
hairs; anterior margin of clypeus lacking minute medial tooth --------- 14

12 Larger species (HW > 1.55 mm); mandible with seven teeth; compound eye

lacking hairs between ommatidia; clypeus with prominent medial carina;

anterior margin of postpetiole not offset from helcium ------ striatinodis

-- Smaller species (HW < 1.35 mm); mandible with six teeth; compound eye

with hairs between ommatidia; clypeus lacking prominent medial carina;

anterior margin of postpetiole offset from helcium -------------------- 13

13 Posterior surface of petiole rugulose-punctate, dull to weakly shining;

in profile, procoxae transversely striate; femur and tibiae smooth

to weakly coriarious, weakly shining to shining ------------------ stefani

Posterior surface of petiole smooth to undulated, shining; in profile,

procoxae finely imbricate; femur and tibiae very strongly coriarious,

dull ---------------------------------------------------------- sylvestris

14 Hairs on head (including psammophore) and mesosoma very short,

thin, and delicate, maximal length similar to width of cephalic

interrugae (note that one to few long coarse hairs are occasionally

present along posterior margin of head and/or pronotum) ------ tenuipubens

-- Hairs on head (including psammophore) and mesosoma not thin

and delicate, maximal length much longer than width of cephalic

interrugae ------------------------------------------------------------ 15

15 Dorsum of mesosoma and posterior surface of petiole rugoreticulate to

vermiculate ----------------------------------------------------------- 16

-- Dorsum of mesosoma usually rugose, sometimes rugoreticulate to

vermiculate; posterior surface of petiole with transverse or oblique rugae

or otherwise, but never rugoreticulate to vermiculate ----------------- 17

16 Small lobe projects dorsally from anterior margin of antennal fossa;

peduncle and anterior surface of petiole meet at obtuse angle; in dorsal

view, posterior surface of petiole narrow, width similar to or only

slightly greater than distance between tips of superior propodeal spines;

mesosomal hairs moderately short, longest rarely > 0.7-0.8x MOD ----------

---------------------------------------------------------- naegelii (part)

-- Lacking small lobe that projects dorsally from anterior margin of antennal

fossa; peduncle and anterior surface of petiole meet at or near right

angle; in dorsal view, posterior surface of petiole distinctly wider than

distance between tips of superior propodeal spines; mesosomal hairs

longer, longest approaching to slightly exceeding MOD - abdominalis (part)

17 Dorsum of postpetiole with transverse rugae -------------------------- 18

-- Dorsum of postpetiole smooth and shining, granulate, punctate, or

otherwise, but lacking transverse rugae (rarely with one to few

longitudinal rugae) --------------------------------------------------- 30

18 Deeply incised fine, regular rugae on head and mesosoma, interrugal

spaces only slightly wider than rugae; humeral angles enlarged, distinctly

elevated above medial portion of pronotum; head and mesosoma black, gaster

dark ferruginous orange --------------------------------------- mendozanus

-- Rugae on head wavy to irregular, not deeply incised, interrugal spaces

distinctly wider than rugae; rugae on mesosoma irregular, rugoreticulate,

or vermiculate; humeral angles flush with to slightly elevated above

medial portion of pronotum; color variable, but if head and mesosoma black

and gaster dark orange, then wide interrugal spaces on head are strongly

granulate ------------------------------------------------------------- 19

19 Interrugal spaces on head smooth to moderately coriarious, weakly shining

to shining ------------------------------------------------------------ 20

-- Interrugal spaces on head moderately to strongly granulate, dull ------ 21

20 Body concolorous black except for dark reddish band encircling eye; rugae

on promesonotum longitudinal, usually regular; rugae at medial occipital

margin longitudinal, rarely rugoreticulate ------------------- “tinogasta”

-- Head and mesosoma dark reddish-black, gaster black; rugae on promesonotum

transverse, oblique, or irregular, rarely longitudinal; rugae along medial

occipital margin usually partly rugoreticulate ------------------ laticeps

21 Body concolorous black ------------------------------------------- atratus

-- Body bicolored or concolorous ferruginous orange, reddish-orange, or

reddish-brown --------------------------------------------------------- 22

22 Head and mesosoma blackish to black, gaster light to dark ferruginous

orange or orangish-black ---------------------------------------------- 23

-- Body concolorous or if bicolored then head and mesosoma not black ----- 24

23 Usually larger (HW = 1.76-2.06 mm); first gastral tergum moderately to

strongly coriarious anterad, dull to weakly shining; pronotal rugae weak

to moderately coarse; medial rugae on mesonotum usually continuing to

anterior margin of pronotum --------------------------------- meridionalis

-- Usually smaller (HW = 1.61-1.81); first gastral tergum weakly to

moderately coriarious, weakly shining to smooth and shining anterad;

pronotal rugae coarse; medial rugae on mesonotum diverging or becoming

transverse to rugoreticulate on pronotum, but not continuing to anterior

margin or pronotum -------------------------------------------- pronotalis

24 Bicolored – head dark reddish-brown, mesosoma and gaster black (mesonotum

occasionally dark reddish-black) --------------------- vermiculatus (part)

-- Body concolorous or if bicolored then mesosoma and gaster not black --- 25

25 First gastral tergum (including posterior margin) moderately to strongly

coriarious, dull ------------------------------------ “semistriata” (part)

-- Posterior margin and usually posterior one-third to one-half or more of

first gastral tergum smooth and shining to strongly shining, rarely

weakly coriarious ----------------------------------------------------- 26

26 Head ferruginous orange to reddish-brown; mesosoma blackish to black

with strong orangish to reddish infusion on promesonotum -------------- 27

-- Head and mesosoma concolorous to nearly concolorous light to dark

ferruginous orange to reddish-brown ----------------------------------- 28

27 Promesonotal suture usually present, pronotum lighter than mesonotum

along suture; interrugae on pronotal sides and mesopleura strongly

granulate, dull; clypeus orangish to orangish-red, concolorous with

adjacent cephalic areas -----------------------------------– “intermedia”

-- Promesonotal suture usually absent, pronotum and mesonotum concolorous

along their juncture; interrugae on pronotal sides and mesopleura weakly

to moderately granulate, dull to weakly shining; clypeus reddish-black to

blackish, notably darker than adjacent cephalic areas --------“maulensis”

28 Anterior surface of petiole meets peduncle at or very near to a right

angle; in profile, gaster dark blackish-red, usually darker than head and

mesosoma –---------------------------------------------------- “chilensis”

-- Anterior surface of petiole meets peduncle at an obtuse angle; in profile,

gaster mostly ferruginous orange, usually concolorous with or slightly

lighter than head and mesosoma ---------------------------------------- 29

29 Antennae blackish, notably darker than cephalic dorsum – “araucania”

-- Antennae orangish, nearly concolorous with cephalic dorsum --- “spinolae”

30 Posterior surface of petiole lacking rugae or rarely with few weak

longitudinal rugae; head and mesosoma usually concolorous dark brown to

black, rarely with blackish head and orangish mesosoma; metanotal sulcus

usually present, weakly to strongly impressed; inferior propodeal spines

well-developed, usually acuminate; propodeal spiracles circular

(brevibarbis-group) -------------------------------------- *** (see below)

-- Posterior surface of petiole with weak to moderately coarse transverse

rugae; head and mesosoma concolorous light to dark ferruginous orange;

metanotal sulcus rarely present; inferior propodeal spines absent to

poorly-developed; propodeal spiracles narrowly ovate ------------------ 31

31 Larger (HW = 1.75-2.05 mm); body concolorous ferruginous orange to

reddish-orange; in frontal view, frontal lobes enlarged, lateral margins

convex, projecting at a strong vertical orientation from cephalic

dorsum -------------------------------------------------------- bispinosus

-- Smaller (HW = 1.24-1.61 mm); head and mesosoma concolorous ferruginous

orange, gaster sometimes blackish; in frontal view, frontal lobes small,

lateral margins subparallel, projecting nearly parallel to cephalic

dorsum ------------------------------------------------------ uruguayensis

*** these species will be treated in separate manuscripts.