Octostruma triquetrilabrum

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

Octostruma triquetrilabrum P jtlc000004551.jpg

Octostruma triquetrilabrum D jtlc000004551.jpg

Specimen Label

Octostruma triquetrilabrum is known from two sites near Monteverde in the Cordillera de Tilarán, and one site in the mountains of western Panama. One Monteverde site is very wet, old-growth montane forest at 800 m on the Atlantic slope, and the other Monteverde site is a small patch of seasonal moist forest at 1150 m, just below the cloud forest on the Pacific slope. All specimens are from Winkler samples of sifted leaf litter. (Longino 2013)

Identification

With the characters of Octostruma wheeleri and Octostruma triangulabrum. Differing from O. wheeleri in the presence of 8-10 spatulate setae on face (6 on O. wheeleri) and shallow reticulate rugulose sculpture on face and dorsal pronotum (nearly smooth on O. wheeleri). Differing from O. triangulabrum in the absence of a pair of spatulate setae on the mesonotum (present in O. triangulabrum); first gastral sternite more uniformly punctate. (Longino 2013)

Keys including this Species

Distribution

Distribution based on Regional Taxon Lists

Neotropical Region: Costa Rica (type locality), Panama.


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.

  • triquetrilabrum. Octostruma triquetrilabrum Longino, 2013: 53, figs. 1A, 3A, 5K, 39, 43 (w.) COSTA RICA.

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

Description

Worker

HW 0.74–0.80, HL 0.68–0.72, WL 0.84–0.88, CI 109–111 (n=2). Matching in almost every respect the description for Octostruma triangulabrum, except the differences outlined in the Diagnosis and key.

Type Material

Holotype Specimen Labels

Holotype worker: COSTA RICA, Puntarenas: Est. Biol. Los Llanos, near Santa Elena, 10.30487, -84.83735, ±100 m, 1150 m, 28 Feb 2004, moist forest, ex sifted leaf litter (J. Longino#5249-s) Instituto Nacional de Biodiversidad, JTLC000004551. Paratype workers: same data John T. Longino Collection, JTLC000004543; same data except Alajuela: Casa Eladio, Rio Peñas Blancas, 10.31667, -84.71667, ±2 km, 800 m, 10 May 1989, wet forest, ex sifted leaf litter on ground (J. Longino#2529-s) California Academy of Sciences, INBIOCRI001281407; 23 May 1990 (J. Longino#2701-s) National Museum of Natural History, CASENT0627377; Museum of Comparative Zoology, CASENT0627378; University of California, Davis, INBIOCRI001282521; Museu de Zoologia da Universidade de Sao Paulo, INBIOCRI001282522; CASC, INBIOCRI001282523.

Etymology

The name refers to the triangular labrum that is not bilobed at the apex. It is a noun in apposition and thus invariant.

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