Octostruma betschi

AntWiki - Where Ant Biologists Share Their Knowledge
Jump to: navigation, search
Octostruma betschi
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Myrmicinae
Tribe: Attini
Genus: Octostruma
Species: O. betschi
Binomial name
Octostruma betschi
Perrault, 1988

Octostruma betschi P casent0280762.jpg

Octostruma betschi D casent0280762.jpg

Specimen Label

Nothing is known about the biology of Octostruma betschi.

Identification

The combination of O. balzani-group mandibles, two pairs of setae on the promesonotum, and flattened setae on the scape uniquely characterize this distinctive species. (Longino 2013)

Keys including this Species

Distribution

Distribution based on Regional Taxon Lists

Neotropical Region: Brazil, French Guiana (type locality), Peru.

Distribution based on AntMaps

AntMapLegend.png

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.

  • betschi. Octostruma betschi Perrault, 1988b: 303, 2 figs (w.q.) FRENCH GUIANA.

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

Longino (2013) - New measurements for the worker are HW 0.51–0.57, HL 0.47–0.53, CI 106–108 (n=4). The queen is reported with measurements HW 0.58, HL 0.55, CI 105 (Perrault, 1988).

Description

Worker

Holotype. Longueur totale environ 1,9 mm, longueur de la tete HL = 0,50 mm, largeur de la tete HW = 0,53 mm, index cephalique CI = 100 HW/HL = 106.

Tete a contour polygonal. Vertex deprime longitudinalement, front concave, en cuvette. Carenes frontales rugueuses, a bord irregulier, saillantes et surplombantes se continuant en arriere de l'oeil puis sous le dessous de la tete jusqu'a la base des mandibules. Oeil enchasse dans la carene, visible de dessus sur les bords de la tete; un poil spatule claviforme en avant de l'oeil et un autre en arriere. Douze poils sur le dessus de la tete, dont 2 paires occipitales, 1 paire sur le vertex et 3 paires sur les cotes de tete. Mandibules allongees avec 7 dents dont 1 dent basale rectangulaire a angles arrondis, une dent apicale en pointe aceree fusionnant a la base avec les deux suivantes; les autres dents sont pointues et epaulees a la base par un denticule plus ou moins distinct. Angle du scape a 90°, arrondi, avec un bord garni de poils spatules claviformes.

Thorax. Stigmate propodeal en position latero-posterieure du fait de l'existence d'une mince lame propodeale. Suture mesoepinotale enfoncee; promesonotum convexe, sans suture. Epines mediaires pointues. Deux paires de poils spatules, l'un sur le dos du pronotum, l'autre en arriere du promesonotum.

Noeud du petiole rectangulaire, un peu arrondi sur les cotes, sa face anterieure faisant un angle obtus avec le dos du pedoncule. Une paire de poils spatules sur le petiole et le postpetiole.

Gastre avec une vingtaine de poils spatules sur la face dorsale et de nombreux poils (souvent arraches) sur la face ventrale.

Teguments de couleur doree sur les appendices, tres legerement foncee sur le corps (un peu rembruni sur d'autres individus). Tegument brillant, a ponctuation dense, contigue mais non confluente, laissant subsister sur l'abdomen une plage tres etroite entre les points qui sont legerement enfonces. Pilosite formee de poils spatules claviformes blanchatres. Pilosite portee par la face ventral des premiers segments du gastre beaucoup plus courte, epaisse, legerement arquee. Pubescence constituee de poils minuscules tres difficiles a voir sur la face dorsale, naissant au fond de chaque ponctuation, le tegument paraissant nu a faible grossissement (contrairement a ce que l’on observe habituellement mais pas toujours chez Octostruma balzani). Grands poils spatules c1aviformes medians, deja enumeres plus haut, alignes d'avant en arriere sur la face dorsale: 2 paires sur le sommet de la tete, 2 sur le pronotum, 1 sur le petiole, 1 sur le postpetiole et 4 sur le premier segment du gastre ; soit 10 paires de poils nettement alignes.

Queen

Syntype. Longueur totale environ 2,3 mm, longueur de la tete HL = 0,55 mm, largeur de la tete HW = 0,58 mm, indice cephalique CI = 100 HW/HL = 105.

Appendices dores, le reste du corps brun-jaune, rembruni sur le vertex. Poils spatules un peu plus nombreux que chez l'ouvriere: 18 sur la tete (dont 1 en avant et 1 en arriere de l’oeil et 1 plus en arriere a une courte distance du bord interne de l’oeil), une vingtaine de poils de calibres inegaux sur le thorax, 1 paire sur le petiole et 1 paire sur le postpetiole, plus d'une vingtaine sur le gastre. Teguments apparemment plus rugueux que chez l'ouvriere, longitudinalement rides sur le mesonotum. Pronotum avec les epaules saillantes et la face anterieure sinuee transversalement. Noeud du petiole transverse, a angles anterieurs aigus, legerement saillants, a cotes divergents vers l'avant. Apex borde d'un fin lisere granuleux rejoignant les deux soies du petiole. Face anterieure legerement concave. Postpetiole en croissant, borde anterieurement et posterieurement par un fin lisere granuleux.

Type Material

Longino (2013) - Holotype worker, paratype workers, queen: French Guiana, [published locality of "5°30'S, 53°W" is incorrect] (J. M. Betsch) Musee National d'Histoire Naturelle] (not examined).

References