Octostruma limbifrons

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Octostruma limbifrons
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Myrmicinae
Tribe: Attini
Genus: Octostruma
Species: O. limbifrons
Binomial name
Octostruma limbifrons
Longino, 2013

Octostruma limbifrons P mcz-ent00511414.jpg

Octostruma limbifrons D mcz-ent00511414.jpg

Specimen Label

The holotype was collected at a cloud forest site in western Panama, in a Berlese sample of forest floor leaf litter.

Identification

Antennal scrobe very shallow, not distinctly margined; face with arcuate carina; frontal carinae and facial arc separated, the termini of the facial arc extend laterally beyond the termini of the frontal carinae (termini of facial arc join frontal carinae in Octostruma ascrobis, Octostruma ascrobicula); facial arc strongly elevated and continuous to juncture with antennal socket, lateral portions of facial arc as strong as frontal carinae (facial arc weaker, lateral portions weaker than frontal carinae in Octostruma convallis, Octostruma convallisur); promesonotum with differentiated anterior and dorsal faces (evenly convex in O. convallis, O. convallisur). (Longino 2013)

Keys including this Species

Distribution

Distribution based on Regional Taxon Lists

Neotropical Region: Panama (type locality).


Distribution based on AntMaps

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Distribution based on AntWeb specimens

Check data from AntWeb

Biology

Longino (2013) - Brown and Kempf (1960) summarized the biology of basicerotines as follows: The basicerotines all come from tropical or subtropical areas, and predominantly from mesic habitats, particularly rain forest, where they live primarily in the upper layers of the soil and in the soil cover, including large and small pieces of rotten wood. They are fairly common in soil cover berlesates. Nests have been found in snail shells, and in the peaty masses gathered about epiphytic ferns above the ground level. So far as is known, colonies are small, consisting of one or more dealate—or rarely ergatoid—females, and a few workers. Judging from the structure of the workers and females, one would suppose that they were predaceous on small arthropods...

Besides this summary, the behavior of three basicerotine species has been studied. Wilson (1956) observed a small captive colony of Eurhopalothrix biroi, a New Guinea species. Workers moved slowly and captured a variety of small, soft-bodied prey, including spiders, symphylans, entomobryid Collembola, campodeids, and hemipteran nymphs. Wilson and Brown (1984) observed a captive colony of Eurhopalothrix heliscata, a species from Singapore. The colony contained over 400 workers, multiple alate and dealate queens, several adult males, and brood. Foraging workers acted "rather like miniature ferrets," readily wedging themselves into small crevices. They foraged solitarily, attacking a variety of prey but mostly termites. They used their sharply-toothed mandibles to abruptly snap onto appendages of prey, maintaining purchase and slowly reaching around with the gaster to sting the prey. The strongly sclerotized labrum was also employed to press against the clamped appendage. The behavioral repertoire was limited. There did not appear to be trophallaxis, as workers and larvae fed directly from prey in the brood chambers. Nor did there appear to be any form of alarm communication. While there was generally an increase in the number of foragers when clusters of prey were presented, there was no evidence of any pheromone-based recruitment. Workers were non-aggressive and responded to disturbance by tucking the appendages and becoming immobile, often for minutes at a time. Wilson and Hölldobler (1986) studied captive colonies of Basiceros manni from Costa Rica and observed behavior not substantially different from E. heliscata. Foraging workers of many basicerotines are often encrusted with a firmly bonded layer of soil, which is thought to function as camouflage, enhancing crypsis (Hölldobler & Wilson, 1986).

Knowledge of the basic natural history of these ants has hardly progressed since the observations of Wilson, Brown, and Hölldobler. More specimens are now available for examination due to quantitative litter sampling, enhancing knowledge of basicerotine diversity and distribution, but discovering nests remains exceedingly difficult. Quantitative samples of 1 m2 litter plots reveals that small basicerotines can be very frequent, occurring in over 50% of samples in some cases, but never in large numbers. Individual samples usually contain fewer than ten workers, and workers are often accompanied by dealate queens. These results suggest that colonies, at least among New World species, are usually small, with tens of workers.

Less than half of the species of Octostruma have their queens described. Ergatoid queens are known from some species. Males are known from collections for some species but none have been described. The mating biology of these ants and how common ergatoid queens are across the genus and within colonies is not known.

Castes

Known only from the worker caste.

Nomenclature

The following information is derived from Barry Bolton's New General Catalogue, a catalogue of the world's ants.

  • limbifrons. Octostruma limbifrons Longino, 2013: 39, figs. 6D, 29, 44 (w.) PANAMA.

Unless otherwise noted the text for the remainder of this section is reported from the publication that includes the original description.

Description

Worker

HW 0.63, HL 0.59, WL 0.65, CI 106 (n=1). Labrum rectangular, formed of strap-like lateral portions joined by a thin translucent lamella; mandibles closed on available specimen, but appear generally similar to O. convallis; dorsal surface of mandible roughened, microfoveolate; scape flattened, with pronounced anterobasal lobe, dorsal surface smooth and shining; clypeus strongly emarginate anteriorly, smooth and shining; frontal carinae sharp, narrow, extending more or less straight back and ending before reaching transverse facial arc; facial arc strongly developed, forming continuous carina that curves forward to join posterior margin of antennal socket, with distinct trough between frontal carina and lateral facial arc; frontal carinae and facial arc delimit anterior face that is shiny, with distinct median longitudinal ruga and faint rugulae laterally, face immediately anterior to facial arc smooth, concave; compound eye small, circular, composed of 4–5 somewhat confluent ommatidia; side of head near compound eye and vertex posterior to facial arc smooth and shiny, with distinct, sparse, uniformly distributed puncta; antennal scrobe below eye, very shallow and not delimited with carina or flange; scrobe surface shiny, punctate; side of head posterior to scrobe completely smooth and shiny, with no puncta; undersurface of head rugose.

Promesonotum somewhat flat-topped, with distinct anterior face rounding into horizontal dorsal face; metanotal groove not impressed; propodeum with a single, concave, sloping surface, not differentiated into dorsal and posterior faces; propodeal spines acute, extending anteriorly as raised carinae that curve medially and join at the metanotal groove, extending ventrally as narrow lamellae, thus posterodorsal propodeum entirely delimited by raised carinae confluent with propodeal spines; a low carina extends transversely across posterodorsal surface, between bases of propodeal spines; propodeal spiracle large, located immediately below propodeal spine and abutting posterior margin; lateral, anterior, and dorsal pronotum smooth and shining with sparse puncta; mesonotum with denser puncta, sculpture differentiated from dorsal pronotum; posterodorsal face of propodeum shallowly foveolate; mesopleuron confluent with side of propodeum, shining, with smooth patches and feeble minute puncta and rugulae.

Petiole in profile with peduncle not differentiated from node, anterior surface sloping evenly from petiolar foramen to node, dorsal face of node sloping posteriorly to projecting transverse cuticular rim, short concave posterior face beneath rim; anteroventral margin with denticle; dorsal face of node faintly foveolate/punctate; postpetiole low, broad, crescent-shaped in dorsal view, dorsal face densely punctate, delimited anteriorly and posteriorly by thin transverse rim; first gastral tergite densely punctate, puncta becoming smaller posteriorly; first gastral sternite punctate with smooth and shining interspaces, puncta larger than on tergite.

Labrum fringed on sides and apex with soft translucent thick setae; each larger mandibular tooth with prominent fully appressed seta; anterior margin of scape with 7 stiff filiform (not clavate) setae, basalmost seta the longest, on apex of anterobasal lobe (lacking a shorter seta proximal to this one, on inner side of lobe); clypeus and face devoid of ground pilosity; face, dorsal mesosoma, petiole and postpetiole lacking erect setae; mesotibia with short, thin, sparse, decumbent ground pilosity, a single large filiform seta and several thin shorter erect setae at apex; mesobasitarsus with several pairs thin, erect setae, apical pair longest; first gastral tergite with 3 stiff filiform setae on posterior margin, following exposed tergites each with row of setae; ground pilosity of first gastral tergite sparse, fully appressed, length of setae subequal to distance between them; first gastral sternite with sparse, thin but stiff erect setae over much of surface except narrow area near postpetiolar insertion.

Color red brown.

Holotype Specimen Labels

Type Material

Holotype worker: Panama, Chiriquí: 24 km W El Hato del Volcan [8.833, -82.754, ±10 km], 1160 m, 26 Jun 1976, cloud forest, ex sifted leaf litter (A. F. Newton) Museum of Comparative Zoology, unique specimen identifier MCZ-ENT00511414.

Etymology

The name refers to the strong facial arc. It is a noun in apposition and thus variant.

References

  • Longino, J.T. 2013. A revision of the ant genus Octostruma Forel 1912 (Hymenoptera, Formicidae). Zootaxa 3699, 1-61. doi:10.11646/zootaxa.3699.1.1