Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
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Images of lectotype (click here).
Range
Mexico to Costa Rica.
Identification
In Costa Rica, sumichrasti is distinguished from the similar monteverdensis by the presence of one or more very long flexuous setae on the tibiae and by a more pronounced, almost tuberculate development of the juncture of the dorsal and posterior faces of the mesonotum. The only other species with similarly long macrosetae on the tibiae is flavosensitiva. The propodeal spines are upturned in sumichrasti, directed posteriorly in flavosensitiva.
Description of worker
Color yellow orange; workers monomorphic in size.
Mandibles striate; clypeus with two to four longitudinal carinulae at anterior margin, anterior margin gently convex; head about as long as wide, subquadrate, with 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 barely surpass margin of vertex; face 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.
Pronotum in lateral profile convex; dorsal face of mesonotum long, flat, somewhat produced, posterolateral margins almost tuberculate, posterior face short, dropping abruptly to propodeal suture; propodeal suture deep in dorsal view but may be more or less obscured in profile due to lateral carinulae that bridge the suture; propodeum with very short, weakly differentiated dorsal face and long posterior face; propodeal spines long, spiniform, upturned; pronotal dorsum mostly smooth and shining, with faint traces of longitudinal carinulae; dorsal face of mesonotum with strong parallel lateral carinae, terminating posteriorly at almost tuberculate juncture with carinulae extending down posterior face, across suture, and onto bases of propodeal spines; medial mesonotum concave, smooth and shining; posterior face of propodeum flat to concave, smooth and shining; side of pronotum smooth and shining; katepisternum and side of propodeum shining, largely smooth with traces of feeble carinulae; mesosomal dorsum with abundant long flexuous amber setae, setae on pronotal humeri and posterolateral mesonotal tubercles very long, subequal in length, longer than anterolateral mesonotal setae; tibiae with abundant long erect setae, of variable length, one or more tibial setae very long, subequal to twice maximum tibial width.
Petiole in side view trapezoidal, smooth and shining or faintly microareolate, with minute right-angle or rounded anteroventral tooth; dorsal face of petiole smooth and shining, longer than wide, widest posteriorly, sides weakly convex, gradually converging to level of petiolar spiracles, abruptly narrowed anterior to spiracles, with about six long amber setae along posterior border; postpetiole with minute subacute to right-angle anteroventral tooth, postpetiole in dorsal view subquadrate and wider than long, with abundant long erect setae; fourth abdominal tergite smooth and shining, with abundant long flexuous erect amber setae, no appressed pubescence.
Measurements:
HL 0.675, 0.563, 0.750; HW 0.751, 0.606, 0.789; HC 0.673, 0.544, 0.730; SL 0.608, 0.525, 0.664; EL 0.182, 0.161, 0.189; A11L 0.245; A11W 0.138; A10L 0.102; A10W 0.121; A09L 0.067; A09W 0.093; A08L 0.052; A08W 0.069; WL 0.801, 0.625, 0.883; SPL 0.157, 0.119, 0.151; PTH 0.181, 0.149, 0.197; PTL 0.244, 0.196, 0.253; PTW 0.220, 0.163, 0.231; PPL 0.189, 0.152, 0.192; PPW 0.242, 0.197, 0.258; CI 111, 108, 105; OI 27, 29, 25; SI 90, 93, 89; PTHI 74, 76, 78; PTWI 90, 83, 91; PPI 128, 130, 134; SPI 20, 19, 17; ACI 0.24.
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 sumichrasti occurs in a wide variety of habitats. It is most common in highly disturbed or urban areas at mid elevation sites, but can occur rarely in mature forest sites and low elevation sites.
Nests are in almost any kind of small cavity. I have collected nests from dead sticks and from cavities in the live stems of Acalypha (Euphorbiaceae). Ward collected nests in Mexico from dead sticks, a live vine stem, and from a swollen-thorn ant acacia. Skwarra (1934a,b), in her study of arboreal ant communities in the state of Veracruz, Mexico, found the species abundantly in a wide variety of nest sites including Cecropia internodes, orchid pseudobulbs, and between overlapping leaves of bromeliads. The types of Forel's surdior were tending aphids beneath the leaf-sheaths of banana (Forel 1885). The types of Wheeler's atitlanica and maya were collected beneath stones in a very dry, open area in Guatemala.
Colonies are polygynous and can have large numbers of dealate queens. Skwarra reported one colony with 31 dealate queens and 962 workers, and another colony with 164 dealate queens and about 1200 workers.
In Costa Rica, sumichrasti is very common in urban areas in and around the capital, San Josˇ. I have found it as an abundant ant in the backyard patios and gardens of several hotels and other dwellings. In these circumstances I have observed columns of workers and dispersed foragers on the vegetation, active both day and night. It is a somewhat less abundant ant along the upper parts of the road from the PanAmerican Highway to Monteverde, where I found small nests in dead sticks along the road edge. A collection that seemed out of place relative to my other observations was a small colony in a live stem of an Acalypha shrub in Hitoy Cerere Biological Reserve, a lowland rainforest site on the southern Atlantic slope. This small colony contained 23 workers and one dealate queen. Finally, a lone worker was collected in a mature wet forest site at 1000m elevation in Braulio Carrillo National Park, on the Atlantic slope of the Cordillera Volcanica Central. The ALAS project carried out an intensive program of sampling at this site, and out of 100 two-week Malaise samples obtained from a set of 20 traps, one sumichrasti worker was found.
Comments
I treat Wheeler's atitlanica as a synonym of sumichrasti. Wheeler was collecting on the north shore of Lake Atitlan in Guatemala, in an area of open sandy soil in hot, dry conditions. He discovered two nests of Crematogaster under stones within about a mile of each other. Each of them contained about 100 adult workers, a small amount of brood, a large number of tiny apterous males, and one or three apterous adult queens respectively. The males and queens were apterous even in the pupal stage. Wheeler considered the workers nearly identical to sumichrasti (which did not stop him from describing them as a new subspecies). The queens and males were also very similar to sumichrasti, differing only in their aptery and, in the case of the males, in details of coloration. Wheeler surmised that the queens and males were workerless social parasites that had invaded and killed the host queen, and that what he was observing was the worker remnants of a sumichrasti colony rearing the brood of the social parasites. He discussed other cases of workerless parasites in ants in which one of the sexes was apterous or had reduced flight capacity. He considered this case to be unique because both sexes were apterous, and he assumed that the queens must mate with their brothers and disperse overland to other host colonies. He commented that in spite of aptery there seemed to be no modification of queen thorax volume or structure. He erected a new subgenus, Apterocrema, and a new species, atitlanica, to hold these putative workerless parasites.
I feel that Occam's razor should be used to trim Wheeler's hypothesis, and that such an elaborate scenario should not be adopted until more evidence for it is marshaled. Until further evidence to the contrary, a more parsimonious explanation is intraspecific plasticity in queen and male development patterns. I have found similar apterous males in monteverdensis, and the small polygynous queens of sumichrasti are not too different from the facultatively produced ergatogynes found in other Crematogaster species such as nigropilosa and curvispinosa. Given the frequency of ergatogynes in the genus as a whole and general indications of developmental plasticity, I suggest that social parasitism is unlikely to be the source of these apterous males. It is more likely to be an intraspecific phenomenon, perhaps facultative and associated with polygyny. We may discover that apterous males occur sporadically in a variety of species.
Synonyms
C. sumichrasti Mayr 1870. Mexico to Costa Rica.
= surdior Forel 1885. Guatemala.
= atitlanica Wheeler 1936. Guatemala.
= maya Wheeler 1936. Guatemala.
Page author:
John T. Longino, The Evergreen State College, Olympia WA 98505 USA. longinoj@evergreen.edu
Date of this version: 19 June 2003.
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