Octostruma batesi

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Octostruma batesi
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Myrmicinae
Tribe: Attini
Genus: Octostruma
Species: O. batesi
Binomial name
Octostruma batesi
(Emery, 1894)

Octostruma batesi P mcz-ent00511301.jpg

Octostruma batesi D mcz-ent00511301.jpg

Specimen Label

Nothing is known about the biology of Octostruma batesi.

Identification

Octostruma batesi is very similar to the widespread Octostruma betschi of the Amazonian lowlands, the latter differing in the presence of appressed spatulate setae on the scape and a somewhat more concave face. Octostruma batesi, O. betschi, and Octostruma stenognatha are all similar in size and head shape and possibly form a clade. Although geographic coverage is poor, the known specimens form an allopatric or parapatric replacement series in South America. However, the provenance of the holotype of O. batesi is uncertain. The type locality, in the original publication and on the specimen, is simply "Amazonas." (Longino 2013)

Keys including this Species

Distribution

Brazil (Amazonas), Ecuador, Bolivia. (Longino 2013)

Distribution based on Regional Taxon Lists

Neotropical Region: Bolivia, Brazil (type locality), Ecuador, French Guiana, Guyana, Suriname.


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

Nomenclature

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

  • batesi. Rhopalothrix batesi Emery, 1894c: 218, pl. 1, fig. 11 (w.) BRAZIL. Combination in Octostruma: Brown, 1949f: 92. See also: Brown & Kempf, 1960: 201; Hölldobler & Wilson, 1986: 17.

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

Description

Worker

Brown and Kempf (1960) - Holotype: TL 2,8, HL 0.64, HW 0.71 (CI 111), WL 0.78 mm. This species is similar to Octostruma balzani, but is a little larger and has more conspicuous, rounded lateral flanges on the occipital lobes behind the compound eyes. Also, the scapes are not so strongly lobiform at the basal angle. We know batesi from only the single holotype worker, so it is impossible to be sure of the status of the species. It could even be an extreme form of balzani. The female is needed before the relationships of this species can be properly assessed.

Longino (2013) - The holotype of O. batesi closely matches three Museum of Comparative Zoology collections I have examined, two from the Andean foothills in Ecuador and one from the Andean foothills in Bolivia. The type is slightly larger than any of the other specimens. Brown and Kempf (1960) examined the holotype and provided measurements HW 0.71, HL 0.64, WL 0.78, CI 111. Measurements of the holotype using the AntWeb image were smaller: HW 0.65, HL 0.59, CI 110. Measurements for one worker each from the three MCZ collections are HW 0.53–0.60, HL 0.50–0.55, CI 107–111.

Type Material

Longino (2013) - Holotype worker: Brazil, Amazonas Museo Civico di Storia Naturale, Genoa (AntWeb image examined, CASENT0904968).

References

  • Brown, W. L., Jr. 1949h. Revision of the ant tribe Dacetini: IV. Some genera properly excluded from the Dacetini, with the establishment of the Basicerotini new tribe. Trans. Am. Entomol. Soc. 75: 83-96 (page 92, Combination in Octostruma)
  • Brown, W. L., Jr.; Kempf, W. W. 1960. A world revision of the ant tribe Basicerotini. Stud. Entomol. (n.s.) 3: 161-250 (page 201, see also)
  • Emery, C. 1894d. Studi sulle formiche della fauna neotropica. VI-XVI. Bull. Soc. Entomol. Ital. 26: 137-241 (page 218, pl. 1, fig. 11 worker described)
  • Hölldobler, B.; Wilson, E. O. 1986a. Soil-binding pilosity and camouflage in ants of the tribes Basicerotini and Stegomyrmecini (Hymenoptera, Formicidae). Zoomorphology (Berl.) 106: 12-20 (page 17, see also)
  • 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