Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
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Image catalog (click here).
Range
Throughout the Neotropics, from southern Texas to Argentina and on numerous Caribbean islands.
Identification
Few to no erect setae on face; sparse short spatulate setae on mesosoma and gaster; short upturned propodeal spines; pronounced anteroventral petiolar tooth; spatulate setae relatively uniformly distributed on first gastral tergite.
Similar species in Costa Rica are torosa, rochai, stollii, and erecta.
Description of worker (Costa Rica)
Color red brown to black; workers usually with pronounced size polymorphism.
In face view head subquadrate, wider than long in larger workers, with emarginate posterior margin; mandibles coarsely striate, striae faint to pronounced; clypeus smooth and shiny or faintly granular or finely longitudinally striate; scapes short, in face view not attaining posterior margin of head when laid back; terminal three segments of antenna gradually lengthening and broadening, becoming increasingly densely pubescent, terminal two segments very much larger, so that antennal club appears two-segmented; scapes with short appressed pubescence, sometimes subdecumbent, never erect, with no differentiated long erect setae (occasionally a long seta on very large workers); face with sparse appressed to subdecument pubescence and sparse short erect setae; face smooth and shining or with variably developed fine longitudinal striation, most common on anterior face and space between eye and antennal insertion, occasionally extending posteriorly and medially, but always with at least median strip sublucid.
Promesonotal profile forming a single, somewhat flat-topped convexity; in large workers promesonotal suture visible, a dorsolateral arch that extends far forward, showing that dorsal pronotum is short and much of promesonotal dorsum composed of mesonotum (approaching queen condition); in small workers promesonotal suture effaced, visible only as oblique anterolateral impressions; propodeum with short but distinctly differentiated dorsal face, such that propodeal suture distinctly visible in lateral view as v-shaped impression; propodeum with long sloping posterior face; propodeal spines short, upturned; promesonotal dorsum and dorsal face of propodeum faintly punctate with varying development of longitudinal or transversely whorled rugulae or striations, lateral carinulae bridge propodeal suture, rarely forming a small triangular denticle; posterior face of propodeum smooth and shining or faintly microareolate; lateral pronotum with faint microsculpture; katepisternum and lateral propodeum faintly punctate to microareolate; promesonotum and bases of propodeal spines with highly variable number but usually abundant short stiff flattened setae; femora and tibiae with appressed to subdecumbent pubescence, no erect setae.
Petiole in lateral view subtriangular, often with slightly concave ventral margin, with strongly developed, anteriorly projecting, acute anteroventral tooth; side faintly granular or microareolate; dorsal face of petiole smooth and shining to faintly microareolate, about as wide as long, subquadrate or more often with convex sides, widest about one third distance from anterior margin, with one or more stiff setae on posterolateral tubercles; postpetiole with no ventral tooth, in dorsal view globular to subquadrate, usually slightly broader than long, rarely with faintly impressed posteromedian sulcus, with four or more stiff setae; fourth abdominal tergite smooth and shining or faintly microareolate, with abundant vestiture of short, stiff, flattened, erect setae, evenly distributed over surface of tergite (not clustered or concentrated anterolaterally).
Measurements:
HL 0.801, 0.616, 1.052; HW 0.869, 0.701, 1.156; HC 0.837, 0.664, 1.123; SL 0.537, 0.454, 0.697; EL 0.175, 0.147, 0.252; A11L 0.248; A11W 0.138; A10L 0.097; A10W 0.113; A09L 0.055; A09W 0.078; A08L 0.034; A08W 0.066; WL 0.844, 0.688, 1.146; SPL 0.134, 0.095, 0.168; PTH 0.174, 0.142, 0.203; PTL 0.239, 0.206, 0.343; PTW 0.253, 0.224, 0.323; PPL 0.198, 0.182, 0.254; PPW 0.246, 0.205, 0.328; CI 108, 114, 110; OI 22, 24, 24; SI 67, 74, 66; PTHI 73, 69, 59; PTWI 106, 109, 94; PPI 124, 113, 129; SPI 16, 14, 15; ACI 0.64.
Description of Queen
A normal queen (dorsal face of propodeum drops steeply from postscutellum and much of propodeum appears ventral to scutellum and postscutellum) with general shape, sculpture, and pilosity characters of the worker.
Natural History
Crematogaster crinosa is an extremely widespread and generalized species that prefers highly insolated habitats. It is common in seasonally dry areas, less common in wet forests. In wet forest habitats it is typically found in the high canopy or in disturbed areas. It may form monodominant populations in mangrove forests.
Colonies are large and polydomous and it is usually difficult to locate colony boundaries. Nests are found in almost any kind of cavity (figs. 1, 2, 4), and columns of workers move from nest to nest. Nests can be in live or dead branches, in small rotten knots, under bark flaps, in cavities in fence posts, opportunistically in ant plants, and thinly dispersed in multiple small bark cavities. Workers, brood, and alate sexuals are dispersed across nests. Small amounts of carton construction are used to form baffles inside of nest cavities and to restrict nest entrances, but large external carton nests are never constructed.
Although new alate queens are relatively common in nests, I have rarely encountered physogastric colony queens. In my collecting experience, I have never found a colony that was obviously polygynous, with many dealate queens dispersed in many nests. However, I am treating Forel's minutior as a synonym of crinosa, and minutior from St. Vincent Island in the West Indies forms large polygynous, polydomous colonies in coastal areas (Forel 1893).
In Colombia I observed the beginning of a nuptial flight just after dusk. I found a dense aggregation of males and workers under a bark flap, and the males were just beginning to fly.
Workers are omnivorous. They are attracted to protein and carbohydrate baits, they scavenge dead or injured insects, they visit extrafloral nectaries, and they tend Homoptera. When nests are disturbed they can be aggressive and will bite. Workers are continuously polymorphic, with a broad range of worker sizes.
I often find cockroach egg cases scattered in the nest chambers of C. crinosa (fig. 1), at a much higher density than in the environment generally. The nature of the relationship between cockroaches and the crinosa group would be worth investigation.
Ecological equivalents are torosa and rochai. I can detect very few behavioral or ecological differences among these species. Crematogaster crinosa is the only member of the group that regularly dominates mangrove habitats. Mangrove forests in Costa Rica are sometimes dominated by Azteca, sometimes by C. crinosa. I found a similar situation in the Santa Marta area of Colombia. I have only one record of rochai from mangroves (a voucher collection from Adams' studies of mangrove communities, Adams 1994), and I have no record of torosa from mangroves. Other than in mangroves, crinosa is less abundant relative to torosa or rochai. For example, a collecting trip to a wildlife refuge in southern Texas yielded 13 separate collections of torosa but only one of crinosa. In northwestern Costa Rica, torosa and rochai are far more abundant than crinosa. Based on museum collections, crinosa seems to be the most common member of the crinosa group on various Caribbean and Pacific islands.
Comments
Members of the crinosa complex are among the most frequently encountered Neotropical ants, particularly in open or seasonally dry habitats. They are geographically variable and taxonomically difficult, and species boundaries are poorly defined. Crematogaster crinosa, rochai, and torosa are three very similar species that occur together in Costa Rica. They are difficult to distinguish and workers may not always be clearly identified. All three have the face with sparse erect setae over short appressed pubescence, the mesosomal dorsum and fourth abdominal tergite with short, stiff erect setae (or erect setae absent), the dorsal face of the petiole short with convex sides, and the propodeal spines short and upturned. Crematogaster crinosa can be differentiated from rochai throughout the range, because crinosa has a dense, even covering of erect setae on the fourth abdominal tergite, while rochai completely lacks these setae or has only a small cluster on each anterolateral humerus. Distinguishing crinosa from torosa is more difficult. In Costa Rica, torosa also has abundant erect setae on the fourth abdominal tergite, but these are usually clustered laterally and anterolaterally, leaving a median strip free of setae. Also, crinosa always has a long, sharp anteroventral petiolar process, while torosa more often has a short, blunt or squared-off process. Crematogaster crinosa can also be confused with erecta and moelleri, but these have flexuous erect setae on the pronotal humeri.
crinosa, torosa, and rochai are extremely close in external morphology. Occasional intermediates occur which can be difficult to assign to one form or the other. Further research is needed to clarify the meaning of these morphological patterns. Are they discrete genotypic clusters with occasionally overlapping phenotypes? Are they not genotypic clusters, but instead caused by selection on relatively few genes that generates complex clinal patterns? If they are genotypic clusters, are they maintained by reproductive barriers or by selection? Do the different morphological forms, species or not, have different ecological characteristics that might explain the geographic and habitat patterns?
Synonyms
C. crinosa Mayr 1862. USA (Texas) to Argentina, Antilles.
= brevispinosa Mayr 1870. Colombia.
= minutior Forel 1893. Antilles Islands, Saint Vincent.
= schuppi Forel 1901. Brazil (Rio Grande do Sul).
= striatinota Forel 1912. Colombia.
= recurvispina Forel 1912. Brazil (Rio de Janeiro).
= sampaioi Forel 1912. Brazil (Rio de Janeiro).
= townsendi Wheeler 1925. Peru.
= chathamensis Wheeler 1933. Ecuador (Galapagos).
 Figure 1a. Flaking bark away on small tree revealed scattered small chambers with workers of Crematogaster crinosa, scale insects, and cockroach egg cases. |
 Figure 1b. Closer view. |
 Figure 1c. Closer view of scale insect. |
 Figure 2a. I found a fresh branchfall with these epiphytic Ericaceae on the ground. |
 Figure 2b. A live stem of the Ericaceae. |
 Figure 2c. Inside was an active nest of Crematogaster crinosa, with abundant brood. |
 Figure 2d. Closer view of nest interior. |
 Figure 3. Workers of Crematogaster crinosa clustered on seedling of Rhizophora in mangrove swamp. I do not know what the attraction was, but workers were very busy at the juncture of the fruit and the cotyledon tube. |
 Figure 4a. A live stem with a small knot. You can see some carton construction covering a nest entrance. |
 Figure 4b. Inside was a small necrotic cavity containing a Crematogaster crinosa nest, which was only a small fragment of a large polydomous colony. |
Page author:
John T. Longino, The Evergreen State College, Olympia WA 98505 USA. longinoj@evergreen.edu
Date of this version: 4 March 2003.
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