Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
Image catalog (click here).
Costa Rica to Amazonian Brazil, Bolivia.
The morphology of this species is quite uniform across its range. It is very similar to brasiliensis, with which it shares the ventral postpetiolar tooth. In Costa Rica the two species are easily distinguishable, because the petiole in lateral profile is elongate and low in brasiliensis, almost linear, with an anteroventral tooth, while in tenuicula it is shorter and taller, more triangular, and lacks an anteroventral tooth. However, in South America the petiole of brasiliensis becomes shorter and taller and the petiole of tenuicula may develop a small anteroventral tooth. The relationship of the posterolateral lobes of the dorsal face to the posterior aperture is consistent across the range of both species, with brasiliensis having a large aperture relative to the lobes and tenuicula having a small aperture.
Crematogaster tenuicula may also be confused with carinata, limata, and foliocrypta. Crematogaster carinata and limata lack a ventral postpetiolar tooth. Crematogaster foliocrypta has appressed tibial pilosity in contrast to the erect pilosity of tenuicula.
Description of worker
Color pale yellow brown to dark red brown; workers monomorphic in size.
Mandibles smooth and shining; clypeus smooth and shining; head about as long as wide, subquadrate, with broadly convex sides and flat to weakly emarginate posterior border; antenna with terminal two segments enlarged to form a club, third segment from end somewhat enlarged, blurring distinction between two and three-segmented club; scapes with abundant long erect setae; when scapes laid back from antennal insertions, they surpass margin of vertex; face largely smooth and shining, with variable extent of striated region between antennal insertion and eye, and whorled above antennal insertion; face covered with abundant long flexuous white setae, no appressed pubescence; in face view abundant setae project from lateral and posterior margins.
Promesonotum in profile similar to brasiliensis, somewhat flattened dorsally, short anterior face of pronotum rises to dorsal face, dorsal faces of pronotum and mesonotum subequal in length, horizontal, forming single flat surface or weakly arched and meeting at a slightly produced angle; dorsal and posterior faces of mesonotum meeting at rounded angle, posterior face dropping to propodeal suture; propodeal suture deep in dorsal view but less pronounced in profile due to lateral carinulae that bridge the suture; lateral carinulae weakly notched, lacking minute triangular teeth at propodeal suture (unlike brasiliensis); propodeal spines medium length, projecting posteriorly; propodeum with short, weakly differentiated dorsal face and long posterior declivity sloping to petiolar insertion; pronotal dorsum smooth and shining or with weakly developed longitudinal carinulae laterally; anterodorsal face of mesonotum with weak, subparallel lateral carinae, these continue onto posterodorsal face as stronger carinae that converge posteriorly, interspace concave, smooth and shining; propodeal declivity smooth and shining; side of pronotum smooth and shining; katepisternum weakly to distinctly punctate or punctatorugose; side of propodeum very faintly sculptured; mesosomal dorsum with abundant long flexuous white setae, setae on pronotal humeri longest; femora and tibiae with abundant long erect setae.
Petiole in side triangular, smooth and shining; anteroventral margin lacking tooth or rarely with a small rounded projection; posterior ring-like aperture that receives postpetiole small, posterolateral lobes of dorsal face of petiole distinctly higher than dorsal margin of aperture when petiole viewed in profile with ventral margin horizontal (unlike brasiliensis, in which posterior aperture is large, dorsal margin at nearly same level as posterolateral lobes of dorsal face); dorsal face of petiole smooth and shining, elongate, widest posteriorly, regularly tapering anteriorly, with long flexuous setae along posterior border; postpetiole with distinct, subacute, short anteroventral tooth, globular in dorsal view, with abundant erect setae; fourth abdominal tergite smooth and shining, with abundant long flexuous erect white setae, no appressed pubescence.
HL 0.641, 0.617, 0.822; HW 0.657, 0.645, 0.884; HC 0.616, 0.579, 0.833; SL 0.656, 0.659, 0.797; EL 0.137, 0.145, 0.199; A11L 0.275; A11W 0.125; A10L 0.142; A10W 0.103; A09L 0.074; A09W 0.069; A08L 0.055; A08W 0.063; WL 0.753, 0.726, 0.913; SPL 0.152, 0.171, 0.173; PTH 0.166, 0.149, 0.213; PTL 0.244, 0.241, 0.349; PTW 0.159, 0.163, 0.230; PPL 0.185, 0.168, 0.203; PPW 0.166, 0.175, 0.232; CI 102, 105, 108; OI 21, 24, 24; SI 102, 107, 97; PTHI 68, 62, 61; PTWI 65, 68, 66; PPI 90, 104, 114; SPI 20, 24, 19; ACI 1.39.
Description of Queen (Costa Rica)
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; sharply bicolored, with red head, mesosoma, petiole, and postpetiole, and black gaster (based on two nest collections, one from Costa Rica, one from near Manaus, Brazil). I cannot find any consistent differences between queens of tenuicula and brasiliensis.
Crematogaster tenuicula occurs in lowland wet forest habitats, in either mature forest or second growth vegetation. In Costa Rica, the species is common on the Osa Peninsula. I have seen only one Costa Rican collection from beyond the Osa, made by D. Olson at Carara Biological Reserve. During my extensive fieldwork in Corcovado National Park in the early 1980's, I frequently encountered tenuicula. Workers built small carton pavilions on low vegetation, covering aggregations of honeydew-producing Homoptera (Coccoidea and Membracidae) that they tended. These carton pavilions were a relatively common site on many different plant species. Isolated workers were common as foragers on low vegetation, visiting extrafloral nectaries and scavenging small dead arthropods. They could be attracted to baits of dead insects or sugar solution. Foragers were active day and night.
Several observations suggest a somewhat diffuse, polydomous nest structure, with spatial segregation of workers, reproductives, and brood of various ages and castes. When baiting, I observed columns of recruiting workers returning to the carton pavilions, within which were workers and Homoptera only. These pavilions never contained brood. In one case, workers recruited to a freshly killed tabanid from two sources: (1) a small, flat chamber under moss on a tree trunk, 50cm high, containing workers only; and (2) a dead, rolled-up leaf lying on the surface of the leaf litter. This leaf contained workers and many winged reproductives of both sexes, but no brood. When I disturbed the ants or watched ants returning with pieces of the bait, they always went to one of these two places. I could not find any more of the colony or any brood. In another case, I found a set of disconnected nests in a vertical, rotten tree trunk. Ants occupied elongate indentations and chambers in the hard outer wood. Again, as in the above case, all the chambers contained mainly adult workers and alates. Some contained large larvae and pupae of reproductives, but I found no chambers with worker brood. I have never seen a definitive nest center with physogastric queen and worker brood.
Beyond Costa Rica I have very little information on the biology of tenuicula. Several of the collections from beyond Costa Rica are from Winkler samples of sifted leaf litter from the forest floor, and Ward collected it "ex Tachigali," an ant plant. One worker was found in stomach contents of a dendrobatid frog from French Guiana.
I once observed a remarkable case of ant mimicry that involved C. tenuicula as the model. I was collecting in northern Guyana near Georgetown and observed a large aggregation of C. tenuicula workers mixed in among nymphs and adults of a leafhopper species (Cicadellidae). The nymphs had a distinctive pattern of black markings on the back that made them look exactly like the Crematogaster workers they were among (Figure). The head and pronotum were black, matching the ant head. The meso and metathorax had a central black mark and four thin black lines radiating laterally, matching the narrow mesosoma and extended legs of the ants. The abdomen had small medial spots anteriorly, these broadening posteriorly to produce the appearance of the petiole and teardrop-shaped gaster of Crematogaster.
John T. Longino, The Evergreen State College, Olympia WA 98505 USA. firstname.lastname@example.org
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