Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
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Image catalog (click here).
Range
USA at least to Colombia, southern limit of species range not defined.
Identification
Differs from C. crinosa in more angular, less tooth-like anteroventral petiolar process; relatively less setose over all; short spatulate setae on first gastral tergite somewhat clustered anterolaterally, leaving a median strip devoid of setae.
Similar species in Costa Rica are crinosa, rochai, stollii, and erecta.
Description of worker
Differing from crinosa in the following respects: mesonotum shorter, promesonotal suture more often impressed, making promesonotal profile flatter; anteroventral petiolar tooth shorter, more often forming nearly right angle rather than long acute tooth; setae on fourth abdominal tergite less abundant, especially medially, such that erect setae more dense anterolaterally.
Measurements:
HL 0.682, 0.578, 1.045; HW 0.763, 0.629, 1.179; HC 0.760, 0.598, 1.123; SL 0.488, 0.443, 0.706; EL 0.170, 0.130, 0.259; A11L 0.241; A11W 0.140; A10L 0.118; A10W 0.118; A09L 0.060; A09W 0.085; A08L 0.041; A08W 0.071; WL 0.789, 0.664, 1.269; SPL 0.080, 0.057, 0.142; PTH 0.165, 0.129, 0.280; PTL 0.232, 0.175, 0.380; PTW 0.246, 0.180, 0.373; PPL 0.171, 0.150, 0.265; PPW 0.224, 0.189, 0.371; CI 112, 109, 113; OI 25, 22, 25; SI 72, 77, 68; PTHI 71, 74, 74; PTWI 106, 103, 98; PPI 131, 126, 140; SPI 10, 9, 11; ACI 0.98.
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 torosa has a biology very similar to crinosa and rochai. It occurs primarily in open, seasonally dry areas, highly disturbed areas, and pasture edges, although it can also be found in the canopy of mature wet forest. In Costa Rica it is a common species in urban areas such as the various city parks in the capital, San Josˇ.
Nests are large, polydomous, distributed in a wide variety of plant cavities. Dead branches and knots in living trees are most often used. In Guanacaste Province in Costa Rica they often occupy ant acacias, and may invade acacias already occupied by Pseudomyrmex. They often construct small carton baffles that restrict nest entrances and small carton pavilions that shelter Homoptera on surrounding vegetation. In some instances they may inhabit cavities in live stems. I found a large nest in the live stems of a Protium branch (Burseraceae) in Corcovado National Park, and I have found nests in live stems of myrmecophytic Acacia and Triplaris. Nest chambers are sometimes filled with alate queens and males. Based on a sample size of two, colony founding is monogynous. In one case I dissected a small colony in south Texas and found a single physogastric queen in the center. In another case I found a lone foundress queen in a dead branch of a Triplaris tree in Costa Rica.
Foraging is primarily diurnal but occasional nocturnal foragers are seen. Workers are generalized scavengers and they frequently visit extrafloral nectaries. Often columns of workers move between nests.
Comments
Specimens of torosa from the northern end of the range, in southeast Texas and in Arizona, are somewhat smaller and less polymorphic than Costa Rican material, but this seems to gradually change as one moves northward in Mexico. Specimens from Baja California are bicolored, with reddish head and mesosoma, and black gaster. However, the abundant material from Arizona and Costa Rica shows continuous variation in the degree of infuscation of the head and mesosoma, and some material may be clearly bicolored like the Baja material. Specimens from Baja nearly always have a long, acute anteroventral petiolar tooth. Specimens from the state of Arizona in the USA and Sonora and Sinaloa states in Mexico (former arizonensis) usually have a short but sharply acute tooth as an average condition, but the tooth form varies from long and spine-like to short and right angled. Specimens from southeastern Texas and Costa Rica show a great deal of variability, but usually have a right-angle tooth and less often a short, sharply acute tooth. They never have a long spine-like tooth. For the time being I interpret all this material as torosa, differing from crinosa and rochai by the somewhat flatter promesonotum and the usually shorter petiolar tooth, and with a gastral setal pattern intermediate between crinosa, which has a uniform covering of flattened setae, and rochai, which has no erect setae.
Synonyms
C. torosa Mayr 1870. USA (Texas) at least to Colombia.
= tumulifera Forel 1899. Nicaragua.
= arizonensis Wheeler 1908. USA (Arizona).
 Figure 1a. Habitat of a vibrant colony of Crematogaster torosa. This is a row of of living fenceposts (Bursera simarouba in this case) along the road from the PanAmerican Highway to Monteverde, Costa Rica. A large C. torosa colony was spread in many cavities along 30m of fenceline. |
 Figure 1b. Nest in a knot. |
 Figure 2a. A second example of a nest in a living fencepost. Arrow shows location of nest. |
 Figure 2b. View of nest entrance. Notice carton construction reshaping nest entrances. |
 Figure 2c. Closer view of carton. |
 Figure 3a. Nest inside live Protium branch (Bursuraceae) from Corcovado National Park, Costa Rica. The branch was covered with carton galleries, from which abundant Peperomia (Piperaceae) sprouted. |
 Figure 3b. Closer view of carton and Peperomia. |
 Figure 3c. Carton removed, revealing hole into branch. |
 Figure 3d. Live branch interior, showing workers, brood, and alate queen. |
 Figure 4a. Celtis tree in south Texas. |
 Figure 4b. Crematogaster torosa tending Coccoidea in fissure in stem of this Celtis tree. Workers were scattered in small cavities. Some cavities had a cap of carton construction. |
 Figure 5. South Texas; Crematogaster torosa nest in cavities in hard, dead wood of mesquite tree. Notice fine dark brown carton partitions, pile of small brood. |
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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