The distinctive feature of these forms is a deeply invaginated propodeal suture and an elevated and compressed dorsal face of propodeum. From my cursory examination, goeldii , stigmatica , and unciata were very similar. They were bicolored, with red brown head and mesosoma and contrasting black gaster. The anteroventral petiolar tooth was moderately well developed and the pilosity was much like torosa . The types of chodati were uniform red brown, and the setae on the mesosoma and fourth abdominal tergite were longer and less flattened. The types of heathi had the coloration of goeldii and the pilosity of chodati . The invaginated propodeal suture is itself a variable character, grading into the condition seen in crinosa and torosa , and so the discussion regarding the forms with striate face applies here as well. Crematogaster goeldii and related forms may be synonyms of other species, multiple distinct species, or one variable species.

It is unclear whether the variation in face sculpture from smooth and shining to completely striate represents intraspecific or interspecific variation. It may be that selection gradients cause parallel changes in face sculpture among multiple sympatric lineages, such that the above forms may be synonyms of crinosa and torosa . For example, I have examined five collections from Colombia that have completely striate faces. Other than the striate face, one collection has the characters of crinosa , three have the characters of torosa , and one has the characters of rochai . Alternatively, further research may reveal that the forms with completely striate faces are found in sympatry with shiny faced forms, or show discontinuous character variation, such that they are best interpreted as distinct species. If so, it must then be determined whether these forms are distinct from each other or should be interpreted as one widespread species.

1 Face appearing somewhat bare, with dilute appressed pubescence, and usually six or fewer erect setae (Fig. 4); if more (up to 20), workers strongly polymorphic and propodeal spiracle very large (Fig. 7A, stollii ); antennal scapes, when laid back, fail to reach posterior margin or only slightly surpass posterior margin; petiole in dorsal view only slightly longer than wide to distinctly wider than long (PTWI> 83), sides convex or straight and parallel, never long and gradually converging anteriorly ...... 2

 

- Face with abundant erect to suberect pilosity; in some cases setae may be somewhat thickened, relatively short, and curved, but still with a relatively uniform vestiture of standing pilosity (Fig. 4); no underlying short appressed pubescence; scape length variable; petiole in dorsal view variable, subquadrate to elongate, with sides straight and subparallel to converging anteriorly, never with strongly convex sides ............. 9

 

2 Postpetiole distinctly bilobed, much broader than long in dorsal view (PPI> 150), with broad median longitudinal sulcus; head somewhat elongate (CI 100-103); scapes when laid back just reach or slightly surpass posterior margin of head; face completely devoid of erect setae ....................................................................... distans

 

- Postpetiole subcircular or subquadrate, not broadly bilobed (PPI <150), median sulcus absent or weakly impressed; head of larger workers distinctly wider than long (CI> 107); scapes variable; face usually with at least one pair of erect setae ........... 3

 

3 Propodeal spiracle very large (Fig. 7A); face with up to 20 erect setae.. .......... stollii

 

- Propodeal spiracle smaller (Fig. 7B); face usually with 6 or fewer erect setae ........ 4

 

4 Pilosity on fourth abdominal tergite composed of abundant filiform flexuous setae, a combination of long erect setae and abundant, long, suberect pubescence ....... crucis

 

- Pilosity on fourth abdominal tergite a combination of completely appressed pubescence, and, when present, a variable number of erect setae; erect setae short, weakly to strongly flattened and stiff ..................................................................................... 5

 

5 Promesonotum with at least humeral setae long and filiform; dorsal face of propodeum short, not distinctly differentiated from posterior face ..................................... 6

 

- Promesonotum with dorsal setae short and stiff; dorsal face of propodeum differentiated or not ................................................................................................................... 7

 

6 Promesonotum with 7-10 medium length flexuous setae .. ............................ moelleri

 

- Only humeral setae long and filiform, other dorsal setae shorter and stiff ....... erecta

 

7 All except the largest workers (HW> 1mm) without differentiated dorsal and posterior faces of propodeum (Fig. 7C); fourth abdominal tergite completely lacking erect setae; anteroventral petiolar tooth well developed, acute and projecting ......... rochai

 

- All workers, even small ones, usually with short, differentiated dorsal face of propodeum(Fig. 7D); fourth abdominal tergite always with at least a few erect setae; anteroventral petiolar tooth variable .......................................................................... 8

 

8 Anteroventral petiolar tooth relatively well-developed and sharp (Fig. 7E); fourth abdominal tergite with abundant setae that are uniformly distributed ............ crinosa

 

- Anteroventral petiolar tooth relatively less well-developed, forming a right or only weakly acute angle rather than a projecting tooth (Fig. 7F); fourth abdominal tergite with moderately abundant setae that are more dense anterolaterally, often leaving a median strip relatively clear of setae .................................................................. torosa

 

9 Petiole in dorsal view elongate and regularly tapering anteriorly; PTWI <73; postpetiolar node tall, globular, usually about as wide as long, rarely wider (PPI 85-124), with no median sulcus; face with abundant long or medium length erect setae, face setae never short and stubble-like; color brown to black, never yellow or distinctly bicolored; face smooth and shiny, not punctate or striate ( limata complex) ........... 10

 

- Petiole in dorsal view relatively shorter, usually subquadrate to rectangular, not tapering anteriorly (if somewhat tapering anteriorly, color yellow or distinctly bicolored, or face with sparse erect setae and abundant shorter curved setae); PTWI> 67; postpetiole variable in dorsal view; face setae, color, and face sculpture variable.... 17

 

10 Propodeal spines very long, directed upward and outward, SPI usually> 34, if in the range 29-33 (small specimens of nigropilosa ) then hind tibia with appressed pilosity .................................................................................................................................. 11

 

- Propodeal spines shorter (SPI <32), if in the range 29-33 (large specimens of limata ) then hind tibiae with erect pilosity; propodeal spines usually directed posteriorly .................................................................................................................................. 12

 

11 Hind tibia with abundant erect setae; setae on face light yellow ............... longispina

 

- Hind tibia with appressed pilosity; setae on face dark amber .. ................. nigropilosa

 

12 Setae on mesosomal dorsum dark amber; mesosoma highly polished, with sculpture confined to lateral carinae of mesonotum; carinae on dorsal and posterior faces of mesonotum meet at strongly angular to tuberculate juncture; tibiae with a combination of appressed short pilosity and scattered long erect setae ................. sotobosque

 

- Setae on mesosomal dorsum light amber to whitish; mesosoma less highly polished, with varying degrees of carinulae and rugulae on pronotum and katepisternum; carinae on dorsal and posterior face of mesonotum may meet at angle, but not produced as a tubercle; tibial pilosity variable, but usually comprised of abundant long erect setae .................................................................................................................................. 13

 

13 Hind tibia with abundant medium-length subdecumbent setae, no long erect setae; petiole with angular anteroventral tooth; postpetiole with no ventral tooth ................ ..................................................................................................................... foliocrypta

 

- Hind tibia with abundant long erect setae; ventral margins of petiole and postpetiole variable .... 14

 

14 Postpetiole with acute anteroventral tooth .............................................................. 15

 

- Postpetiole lacking anteroventral tooth ................................................................... 16

 

15 Petiole relatively triangular in lateral view (PTHI>60), usually lacking anteroventral tooth; posterodorsal tubercles distinctly higher than posterodorsal margin of tergite (Fig. 7G) ....................................................................................................... tenuicula

 

- Petiole relatively elongate (PTHI <60 in Central America, variable and often higher in South America), with angular to acute anteroventral tooth; posterodorsal border of petiole low, posterodorsal tubercles little higher than posterodorsal margin of tergite (Fig. 7H) ......................................................................................... brasiliensis

 

16 Petiole with angular anteroventral tooth; propodeal spines short (SPI <21) .... carinata

 

- Petiole usually lacking anteroventral tooth; propodeal spines long (SPI> 25) .... limata

 

17 Face largely punctate or otherwise heavily sculptured, with smooth and shiny portion restricted to a median strip ................................................................................ 18

 

- Face largely smooth and shining, with at most small areas of punctation between eye and antennal insertion ............................................................................................. 22

 

18 Tibiae with abundant erect setae; size relatively large (WL> 0.70) ....................... 19

 

- Tibial pilosity fully appressed, not erect; size relatively smaller (WL <0.73) ........ 21

 

19 Dorsal setae on mesosoma and fourth abdominal tergite dark amber; propodeum somewhat inflated; propodeal spines very thin and needle-like (Fig. 7I,J) ..... arcuata

 

- Dorsal setae whitish; propodeum less inflated; propodeal spines more broadly tapering to base (Fig. 7K,L,M,N) ..................................................................................... 20

 

20 Propodeal spines relatively thinner and less diverging, more posteriorly directed in dorsal view (Fig. 7K,L); dorsal and posterior faces of propodeum not well differentiated, more or less in same plane; anteroventral margin of petiole with a low, rounded tumosity but lacking distinct angle or tooth; anteroventral margin of postpetiole with bluntly rounded projection, lacking sharp tooth ............................................. evallans

 

- Propodeal spines stout and diverging (Fig. 7M,N); dorsal and posterior faces of propodeum differentiated, not in same plane; anteroventral margin of petiole developed as distinct right to acute angle; anteroventral margin of postpetiole with sharp, acute tooth .... ............................................................................................................. acuta

 

21 Propodeum somewhat inflated, with propodeal spines reduced to small denticles; anteroventral petiolar tooth lacking .......................................................... montezumia

 

- Propodeum not inflated; propodeal spines well-developed; anteroventral petiolar tooth well-developed .................................................................................... obscurata

 

22 Color uniformly yellow or orange.. ......................................................................... 23

 

- Color amber to dark brown or black, or bicolored with dark head and gaster, lighter mesosoma .... .......................................................................................................... 28

 

23 Mid and hind tibiae with one or more very long erect setae, much longer than maximum tibia width ....................................................................................................... 24

 

- Mid and hind tibiae with appressed to suberect setae, none longer than maximum width of tibia ........................................................................................................... 25

 

24 Propodeal spines upturned; erect setae on pronotal humeri and posterolateral mesonotum very long, subequal in length, longer than setae on anterolateral mesonotum (Fig. 7O) ............................................................................... sumichrasti

 

- Propodeal spines directed posteriorly; erect setae on pronotal humeri and anterolateral mesonotum the longest, longer than setae on posterolateral mesonotum (Fig. 7P) ................................................................................................................ flavosensitiva

 

25 Eyes very small (OI <23); erect setae on face and mesosomal dorsum relatively short, somewhat stiffened, forming a stubble; propodeal spines short, upturned ........ ................................................................................................................. flavomicrops

 

- Eyes larger (OI> 24), erect setae on face and mesosoma longer and thinner; propodeal spines variable .............................................................................................. 26

 

26 Pair of setae on posterolateral mesonotum subequal in length to humeral setae; propodeal spines relatively long, upturned .............................................. monteverdensis

 

- Propodeal spines of variable length, upturned or directed posteriorly; humeral setae much longer than any setae on mesonotum ............................................................. 27

 

27 Propodeal spines short (SPI 15-18); mesosoma relatively compact in lateral profile (Fig. 7Q) ................................................................................................... minutissima

 

- Propodeal spines long (SPI 18-21); mesosoma more elongate in lateral profile (Fig. 7R) ............................................................................................................................. wardi

 

28 Tibiae with setae fully appressed ............................................................................. 29

 

- Tibiae with abundant erect setae .............................................................................. 31

 

29 Postpetiole much wider than long (PPI> 138); setae on face short, flattened, curved or slanted toward median axis; anteroventral margin of petiole lacking angle or tooth; ventral margin of postpetiole with rounded lobe, without acute tooth .............. ....................................................................................................................... abstinens

 

- Postpetiole more globular (PPI <132); setae on face of variable length and stiffness, but not strongly curved or slanting toward median axis; anteroventral margin of petiole with subacute tooth or at least blunt lobe; ventral margin of postpetiole with obtuse to acute tooth ................................................................................................ 30

 

30 Propodeal spines regularly tapering from base to tip (Fig. 7S) .................. bryophilia

 

- Propodeal spines in dorsal view with bases thickened, directed outward, tips short, abruptly narrowed and directed posteriorly (Fig. 7T) .............................. curvispinosa

 

31 Propodeal spines forming angular tumosities, not spiniform, or with at most a minute spiniform denticle .................................................................................. raptor

 

- Propodeal spines distinctly spiniform ...................................................................... 32

 

32 Ventral margin of postpetiole with acute to right angled tooth; propodeal spines relatively long and upturned (SPI 19-23); postpetiole gradually constricted toward helcium; mesosoma often light brown, contrasting with dark brown head and gaster ..... ........................................................................................................................ snellingi

 

- Ventral margin of postpetiole flat, completely lacking tooth; propodeal spines relatively short and posteriorly directed (SPI 13-18); postpetiolar node abruptly constricted, with clearly defined juncture with cylindrical stem of helcium; head, mesosoma, and gaster uniformly dark brown.. ............................................. jardinero

(Species with an asterisk have not been collected in Costa Rica but are known from nearby sites in Panama: Volcan Chiriquí or Barro Colorado Island.)

WORKER CHARACTERS

 

The terminal segments of the antenna are enlarged to form the antennal club. The club may be composed of the terminal two segments and sharply differentiated from segments eight and nine, or it may be composed of the terminal three or four segments, which gradually decrease in size. Although the number of segments in the club has been used as a subgeneric character (Santschi 1918), I find continuous interspecific variation (Figure 3) that does not correlate with other characters, and I do not use the character in the key.

 

The petiole varies greatly in shape and seems to be one of the most useful characters for differentiating clusters of species (Plates 1-3). In dorsal view the petiole has a large, flat anterodorsal face. The posterior border is usually well defined by two posterolateral angles or tubercles, these usually surmounted by one or two setae. A transverse carina or ridge unites the posterolateral tubercles. A very much shorter posterior face drops to the cylindrical posterior aperture of the tergite, which tightly invests the anterior rim of the helcium (the specialized anterior portion of the postpetiole, which articulates with the petiole; see Bolton 1994). When the anterodorsal face of the petiole is viewed from above, perpendicular to the line of sight of the viewer (this can be achieved by pushing the gaster down or removing the metasoma entirely and remounting it) it may be (1) elongate and tapering anteriorly to a narrow neck just posterior to the condyles that articulate with the propodeum; (2) rectangular to quadrate, with subparallel sides and an abrupt constriction anteriorly; and (3) short with broadly convex sides, distinctly widest at the middle. Although these three character states are not always sharply differentiated and intermediate forms occur, clusters of species can be clearly placed into one of the three categories. A fourth condition is characteristic of the major radiation (or radiations?) of temperate zone species. The anterodorsal face is short, with strongly convex sides that are strongly expanded anteriorly, such that the petiole is widest anteriorly. Species with this character state (subgenus Crematogaster s.s., see Buren 1959) are restricted to the temperate zone and subtropics, and do not occur in Costa Rica.

 

The ventral margins of the petiole and postpetiole exhibit varying degrees of development of an anterior tooth. These anteroventral teeth are independent of each other, appearing on the petiole alone, on the postpetiole alone, on both, or on neither. They appear to be evolutionarily labile because they are not highly correlated with other characters and do not unite clusters of related species the way petiole shape seems to. Nevertheless, they are often reliable species-level characters: they correlate well with particular suites of characters that are hypothesized to be diagnostic for particular species. A clear view of the anteroventral margin of the petiole and postpetiole is often essential for species identification.

 

The postpetiole is comprised of the thickened rim of the anterior helcium, the narrow "neck" of the helcium, and the broadened and elevated node. The neck of the helcium may be short and cylindrical, forming a relatively sharp juncture with the node, like a stem on an apple. Alternatively, the neck may be relatively elongate and gradually tapering such that the juncture with the node is not sharply defined. In this case the dorsal view of the petiole is somewhat hour-glass or flask shaped. In the latter case, the node is globular, about as wide as long, and with no trace of a median longitudinal sulcus. In the former case the node is less globular, relatively more dorsally compressed, subquadrate in dorsal view, and usually distinctly wider than long. When the node is broad and subquadrate, it may exhibit some degree of development of a median longitudinal impression or sulcus. At extremes, the sulcus is very well defined, dividing the postpetiolar node into two distinct lobes, with a strong posterior emargination and a fully impressed sulcus.

 

Pilosity characters, like petiolar characters, are very useful and seem to unite clusters of related species. Pilosity on the face usually falls into one of three categories: (1) abundant long erect flexuous setae; (2) abundant short stiff setae, forming a stubble of straight or curved setae; or (3) largely or entirely bare, with a vestiture of sparse, very short, completely appressed hairs (a very dilute and appressed pubescence) and a small number of longer erect setae (Fig. 4). Pilosity on the meso and metasomal dorsum varies in density and may be composed of long flexuous or short stiff setae. Tibial and scape pilosity may be appressed or suberect and varies in length. When tibial pilosity is erect, it is usually subequal in length to the maximum width of the tibia, but in a few species there are 1-3 specialized longer setae that are about twice as long at the others.

 

Subgeneric classifications were proposed for Crematogaster by Santschi (1918), Emery (1922), and Wheeler (1922b). Wheeler's key was largely a translation of Santschi with few modifications. The main characters used to distinguish subgenera in the Neotropics were (1) the number of segments in the antennal club, (2) whether the anterodorsal face of the petiole was widest posteriorly or anteriorly, and (3) whether the postpetiolar dorsum had a median sulcus. In practice it is difficult to use any of these characters to sharply divide groups of species. Although I suspect these characters will prove phylogenetically informative, this work does not purport to establish phylogenetic hypotheses. Its purpose is to improve the species-level alpha taxonomy of the Neotropical species and provide a key for the Costa Rican fauna. Evaluating the status of subgenera must await further research, and they are ignored in this work.

 

QUEEN CHARACTERS

 

Queens are known for 27 of the 33 species that occur in or near Costa Rica. Normal queens are similar to workers in general shape, sculpture, and pilosity characters, differing in typical caste-specific traits: larger size, ocelli, enlarged mesosoma with additional sclerites, wings or wing scars, and enlarged gaster. As discussed in the Natural History Overview, acuta-group queens are more strongly differentiated from workers, often with highly polished integument and/or distinctive pilosity traits. There is variation in queen size (Fig. 5) and in the relationship of queen size to worker size (Fig. 6). Queens are given very cursory treatment in this work. Size relationships are depicted in Figures 5 and 6, and brief descriptions are provided in the species accounts.

Natural History Overview

 

Crematogaster are often common ants, and they play a major ecological role in Neotropical forests. Colonies may be large, blanketing forest canopies, or small, contained within a single dead twig. Large colonies are usually polydomous, with multiple nests. Most species nest in dead wood, from narrow gauge hollow stems to large dead branches or trunks. One species, C. stollii , nests in live stems. Although major Crematogaster lineages in the Asian and African tropics are specialized plant ants, and at least one or two species are plant ants in the Amazonian region, none are known to be specialized plant ants in Costa Rica. Crematogaster bryophilia often nests under epiphyte mats. Although many species can make carton from masticated plant fibers, most use relatively small amounts to form partitions inside the nest or to restrict the opening of a nest in dead wood. Several Costa Rican species use carton more extensively. Crematogaster stollii makes carton galleries on tree trunks and branches, connecting their nests in the live branch tips. These carton galleries are indistinguishable from those of Azteca forelii , an ant species with similar nesting behavior, and both are very similar to the galleries of the arboreal termites that are so common in lowland forests. Crematogaster montezumia and C. arcuata make external carton nests that encircle small stems. These nests are plain carton, and lack epiphytes. In contrast, two Costa Rican species make carton nests that sprout epiphytes, forming ant gardens. Crematogaster longispina makes loose ant gardens on tree trunks (Kleinfeldt 1978), and C. jardinero lives in the high canopy, forming "archipelago" clusters of discrete ant gardens.

 

Although most species are arboreal, a few nest in the leaf litter. Species that nest in the leaf litter are usually yellow, nocturnal, and rarely encountered. One leaf litter species, C. sotobosque , is brown, forages diurnally on low vegetation, and is moderately abundant in lowland wet forest.

 

Most species are monogynous; a few are polygynous. Ergatogynes or intercastes have been reported for C. minutissima (Holliday 1903), C. minutissima smithi , and a species tentatively identified as C. curvispinosa (Heinze et al. 1998, Heinze et al. 1999). The Heinze et al. studies of smithi revealed that these intercastes, morphologically intermediate between workers and queens, function mainly to provide trophic eggs for the colony. They never perform foraging, maintenance, or defensive duties. They mainly lay eggs, most of which are eaten by larvae. The ergatogynes lack a spermatheca and cannot be inseminated, but their eggs are viable and produce males if left to develop. Among the Costa Rican fauna, ergatogynes are known to occur in C. bryophilia , C. curvispinosa , and C. nigropilosa . Nests are often found with only ergatogynes, workers, and brood. It is unknown whether these are colony fragments, with queenright nests elsewhere, or whole colonies founded by ergatogynes.

 

Two categories of queens occur among the Costa Rica fauna. In one group the propodeum is tall and narrow and drops very steeply from the scutellum (Fig. 1A), and sculpture and pilosity characters are similar to workers. I refer to these as "normal" queens. These species appear to have typical colony founding behavior, with standard nuptial flights and claustral colony founding by individual queens, and they are the most abundant species in communities. In another group the propodeum has a shallower slope and extends well beyond the scutellum (Fig. 1B), and sculpture and pilosity characters often differ greatly from workers. In particular, queens are often highly polished and shiny. Queens in this group also show varying degrees of development of falcate mandibles. Costa Rican species having these distinctive queens are acuta , arcuata , distans , evallans , jardinero , montezumia , and raptor . I refer to these as the "acuta-group." These are all very low density species, and very little is known of their colony founding behavior. The morphology is similar to other ant lineages that are known to be temporary social parasites (Forel 1928, Hölldobler and Wilson 1990). Queens of temporary social parasites insinuate themselves into nests of other species, killing or incapacitating the host queen, and use the heterospecific worker force to establish their own colony. Two anecdotal observations are consistent with temporary social parasitism as a colony founding mechanism in the acuta-group. I observed a mixed nest in which a queen of C. montezumia occurred in a small nest with workers of C. curvispinosa , and Adrienne Nicotra, a student working at La Selva Biological Station, observed a queen of C. raptor in a small queenright nest of C. carinata . These are the only such observations so far, and the colony founding behavior of acuta-group species is in need of investigation.

 

Most species of Crematogaster , especially those with large polydomous colonies, are aggressive and territorial. Crematogaster carinata is exceptional in having large polydomous and polygynous colonies that overlap with many other ant species. Workers are not aggressive and may even share the same nest structures with other species. Forel (1898) observed C. carinata (as C. limata parabiotica ) and Dolichoderus debilis Emery inhabiting the same nest in Colombia, and coined the term parabiosis to describe the phenomenon of mutual nest sharing. In Costa Rica, C. carinata can be found coinhabiting ant gardens with Odontomachus panamensis Forel and sharing nest space with D. debilis or D. inermis Mackay . The nesting behavior and taxonomic uncertainties in the complex are further discussed under the C. carinata species account. Crematogaster limata may also exhibit an ability to overlap non-aggressively with other species because it has been observed in close association with the large tropical ponerine ant Ectatomma tuberculatum (Olivier) (Wheeler 1986).

 

Crematogaster appear to be very generalized and omnivorous foragers. Individual scouts search for resources and recruit nestmates when resources are encountered. They rapidly recruit to baits of sugar or protein (e.g., tuna, dead insects). Although rarely predators of active prey, I have often seen them attacking pupae or otherwise immobilized live prey. They readily tend Homoptera, and species vary in the degree of reliance on Homoptera. Crematogaster stollii appears to rely entirely on Homoptera and perhaps cryptic plant resources. Workers are found only inside of live stems or under their carton galleries and they never forage on the surface. Their chambers in live stems are packed with Coccoidea that are feeding from the inside of the stems. This phenomenon, in which ants live and feed entirely within live plant stems, with no external patrolling by the ants and no obvious myrmecophytic adaptations on the plant's part, has evolved convergently in several ant lineages, including species of Azteca and Myrmelachista .

 

In Costa Rica, Crematogaster are abundant in all lowland habitats. In mangroves, C. crinosa is often a dominant species. In lowland dry or wet forest sites, a community of over 15 species may occur. These are concentrated in second growth vegetation, forest edges, and forest canopy. Relatively few species are found in wet forest understory and forest floor litter. At higher elevations the dominant Crematogaster drop out by about 500 to 1000m, depending on the openness of the habitat. A few species, such as C. bryophilia , C. moelleri , and C. sumichrasti , are montane forest specialists that are more common at mid elevations than at sea level.

Most species are tropical, where they form dominant elements of the arboreal fauna. Some species groups have crossed the frost line, radiating in temperate zones, where they more often nest in the ground and beneath stones (Wheeler 1906).

 

The genus as a whole is clearly monophyletic, with a unique and apomorphic arrangement of postpetiole and gaster. The gaster has a tear drop shape, pointed posteriorly, and the postpetiole attaches to the dorsal surface of the fourth abdominal tergite. Thus the gaster is suspended beneath the postpetiole rather than being clearly posterior to it. The petiole has no dorsal node, and when the gaster is elevated the petiole fits flush against the propodeum. This combination of characters is probably related to defensive or offensive behavior in which workers wave their gasters in the air, exuding a droplet of venom onto the spatulate sting (Buren 1959). Not all species exhibit this behavior (D. Davidson, pers. comm.) but most do. Workers are monomorphic or exhibit continuous size polymorphism, but there is no distinct major worker caste. The antennae are 11-segmented with the exception of one lineage of Asian and African species, in which there are 10 segments. The antennae have a terminal club of 2-4 segments. The propodeum usually has a pair of dorsal spines (lack of spines is rare among New World species), but otherwise the workers lack armor.

 

At the species level the genus can appear somewhat monotonous because there is little variation in major shape characters. Nevertheless species diversity is high, both within local communities and globally. Species differ in details of petiole and postpetiole shape, overall pilosity characteristics, and surface sculpture. Because the genus is a common and conspicuous element of most faunas, especially in the tropics, and varies both within and among regions, 889 available names have been generated (Bolton 1995). Nearly all of these have accumulated as unconnected species descriptions and there are very few synthetic works (Buren's 1968 review of North American Crematogaster s.s. a notable exception). Attempts have been made to recognize subgenera, but they are not well supported nor well defined. The high species diversity and lack of higher level taxonomic structure in the genus has made it one of the intractable messes in the world of ant taxonomy, on par with Solenopsis and Pheidole . It is a group generally avoided by students of systematics seeking manageable projects.

Crematogaster is one of the largest and most sharply defined genera in the family Formicidae. The species are all small, with monomorphic worker, decidedly larger female, and the male usually as small as the worker. The worker and female have 10- or 11-jointed antennae, those of the male are usually 12-jointed. All the phases can be readily recognized by the peculiar structure and articulation of the petiole and postpetiole. The former does not bear a node but is more or less flattened above, the latter is short and articulated to the anterodorsal surface of the gaster, instead of to its anterior end as in other ants. The gaster, moreover, is in the worker and male subtriangular or subcordate, with pointed tip, and its upper surface is concave or more or less flattened, its ventral surface more convex and protuberant. These peculiarities in the structure of the abdomen enable the workers of many species to turn the gaster forward over the thorax and head, so that they are sometimes called "acrobat ants." As a rule, the sting is feebly developed. The anterior wings of the male and female have a discoidal and a single closed cubital cell.

 

The species of Crematogaster all form populous colonies which nest in the ground, under stones, in logs, the cavities of living plants, or in peculiar carton nests attached to the branches or trunks of trees. This habit of making carton nests is best seen in the tropical species, but traces of it survive even in the species inhabiting temperate regions, such as the North American C. lineolata (Say) . Many of the species have rank and disagreeable odors.

 

The genus is cosmopolitan (Map 22), though the species scarcely enter the colder portions of the north and south temperate zones. Our common C. lineolata (Say) of North America occurs, however, as far north as Nova Scotia. The vast majority of species are confined to the tropics, being particularly numerous in the Neotropical and Ethiopian Regions. The African forms are so numerous and so variable that they constitute a veritable welter of subspecies and varieties. Mayr, Forel, Arnold, and Santschi have all dispaired of reducing this chaos to order. Unfortunately the portion of Arnold's work dealing with the South African species has been postponed by the war. He has, however, kindly written me concerning certain necessaly changes in the synonymy of several of the species and I have adopted his interpretations in the list of Ethiopian species (Part VIII). Dr. Santschi, who has given more attention to the African species of Crematogaster than any previous author, has generously examined and identified a series of all the Congo forms collected by Lang, Chapin, and Bequaert and has written the descriptions of several new forms. In the meantime he has published a revision of the subgenera of Crematogaster .1 Forel was the first to begin the splitting of the genus, but Santschi has added several new subgenera. A translation of his table has been included in the key to the genera and subgenera of Myrmicinae. Santschi has arranged these various subgenera according to their natural affinities in the following sequence:

 

Map 22. Distribution of the genus Crematogaster .

 

Of these, at least seven, Decacrema , Orthocrema , Sphaerocrema , Crematogaster , Atopogyne , Oxygyne , and Nematocrema occur in the Ethiopian Region. In the Congo material before me only Sphaerocrema , Crematogaster , Atopogyne , and Nematocrema are represented.

This large cosmopolitan genus is represented in California by both arboreal and groundnesting species. Nine species have been recorded from the state but taxonomic uncertainties undermine this statistic. C. opuntiae Buren is quite similar to, and possibly conspecific with, C. californica Wheeler ; the differences between C. coarctata Mayr and C. mormonum Wheeler are slight and unreliable; and the record of C. larreae Buren from California may be a misidentification. The North American species of this genus are much in need of a taxonomic update.

 

Species identification: keys in Buren (1968b). Additional references: Buren (1959), Longino (2003), Mackay and Mackay (2002), Scheffrahn and Rust (1989), Snelling and George (1979), Wheeler and Krutzsch (1994).

Boquerón , Paraguarí (ALWC).

Canindeyú (ALWC).

Crematogaster Lund, 1831: Annls. Sci. Nat. 23:132.

 

Type-species: Formica scutellaris Olivier , 1791: Encyl. Meth. Hist. Nat. Insec. 6:497.

 

Distribution: Palaearctic, Ethiopian, Oriental, Australian, Nearctic & Neotropical regions.

Des ouvrieres de T 44: Nion (LaMOTTE) et des mousses de la foret N.-E. (VILLIERS) se rattachent au groupe nigrans-lamottei, mais sont molles et immatures, indeterminables avec certitude.

Formica , pt., Oliv. Encycl. Meth. vi. 497 (1791).

 

Myrmica , pt., Latr. Hist. Nat. Fourm, 261 (1804).

 

Crematogaster , Lund, Ann. Sc. Nat. xxvii. (1831).

 

Acrocoelia, Mayr. Ein. neue Ameis. 143 (1852).

 

Maxillary palpi 5-jointed, labial palpi 3-jointed. Antennae 11-jointed, the club 3-jointed. Anterior wings with one marginal cell, incomplete; one complete submarginal, and one discoidal cell. Abdomen cordate, the petiole attached to the upper surface of its base.

 

The insects belonging to this genus of Ants construct their nests on the branches of trees, suspending them in the same way as Wasps, to the nests of which they have a close resemblance; on removing the outer covering, however, they exhibit a very different construction, being composed of multitudinous, curved, intricate ramifications, all leading to the interior chambers and galleries. From the close resemblance which the nests have to a wig, they have probably acquired the popular name of the Negro-head, by which they are generally known in the Brazils. The insects are readily known in consequence of the abdomen being usually heart-shaped, and the peduncle by which it is attached to the thorax being inserted at the top of the basal segment, instead of beneath, as it is in all the other genera of Ants. These insects are described by observers as having a remarkable appearance when running about, as at such times they curve the abdomen upwards, so that it partly overhangs the thorax behind.

Running on waxy leaves: Arboreal ants
 

Arboreal ants can walk on waxy plant leaves, with attachment forces from 50 to 150 times their weight.

     
  "Even less clear is the basis of 'wax-running,' by which some ants get around on the slippery epicuticular wax of plants. Federle, Rohrseitz, and Hölldobler (2000) measured attachment forces by making ants do their thing under varying amounts of extra gravity in a centrifuge. Scaling pointed to detachment force as dependent on contact area, but, paradoxically, ability to wax-walk turned out to vary inversely with attachment strength to a smooth acrylic (Plexiglas/Perspex) plastic. Whatever the mechanism, arboreal ants hang on spectacularly; attachment forces from 50 to 150 times their weights exceed those of all other insects yet investigated." (Vogel 2003:430)
  Learn more about this functional adaptation.

Collection Sites: world map showing specimen collection locations for Crematogaster

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The following is a representative barcode sequence, the centroid of all available sequences for this species. 

 
There is 1 barcode sequence available from BOLD and GenBank.   Below is the sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.  See the BOLD taxonomy browser for more complete information about this specimen.  Other sequences that do not yet meet barcode criteria may also be available.
 

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