Octostruma petiolata

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Octostruma petiolata
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Myrmicinae
Tribe: Attini
Genus: Octostruma
Species: O. petiolata
Binomial name
Octostruma petiolata
(Mayr, 1887)

Octostruma petiolata P mcz-ent00511355.jpg

Octostruma petiolata D mcz-ent00511355.jpg

Specimen Label

Nothing is known about the biology of Octostruma petiolata.

Identification

This species is known from southern Brazil. Workers can be identified by the combination of strongly transverse petiolar node in dorsal view, mesosoma lacking erect setae, large size (HW 0.85–0.90), and strong laminar transverse carina joining the propodeal spines. I examined a worker from Itajubá, Santa Catarina State (MCZ). (Longino 2013)

Keys including this Species

Distribution

Distribution based on Regional Taxon Lists

Neotropical Region: Brazil (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

Nomenclature

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

  • petiolata. Rhopalothrix petiolata Mayr, 1887: 580 (q.) BRAZIL. Emery, 1894c: 217 (w.). Combination in Octostruma: Brown, 1949f: 92. See also: Brown & Kempf, 1960: 182.

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) - 6 specimens, from two different localities): TL 3.3-3.5, HL 0.74-0.78, HW 0.85-0.90 (CI 114-117), WL 0.89-0.92 mm.

Queen

Brown and Kempf (1960) - Alate (3 specimens, including 2 syntypes): TL 5.2-5.5, HL 0.98-1.00, HW 1.14-1.20 (CI 116-120), WL;.45-1.53, forewing L 4.7-5.1 mm.

This species, described from the female caste, has workers so different in habitus, and especially in sculpture and ground pilosity, that only examination of the workers and female associated by Emery (lac. cit.) from "5. Paulo" (von Jhering leg.) finally convinced us that they belong together. Curiously, Emery's characterization of the worker does not bring out the outstanding differences. In addition to the size and head form differences, the worker has the head, alitrunk and both nodes very minutely and superficially shagreened, so that the surface is smooth but opaque. The gaster is more lightly -shagreened and is weakly shining to subopaque, with feeble punctulation over the surface. The female has the head and pronotum distinctly vermiculate-rugulose; scutum longitudinally subcostulate and shallowly punctate; scutellum transversely rugulose. The nodes are shagreened, with weak punctation, and the gaster is densely and finely punctate and opaque. The alitrunk is very convex, both from front to rear and from side to side in the worker; the dorsal sutures are absent in the two worker specimens seen, but the dorsum of the propodeum forms a slight angle with the promesonotum where they join. Propodeal teeth short and triangular in both female and worker. The six workers seen had the erect clavate hairs confined to the head, scapes, legs and gastric apex and venter, but the dorsal surfaces of the body, except the upper central part of the head, have abundant fine appressed hairs. A pair of fine long hairs anteromedially on first gastriC sternite. The female has, in addition to the rather abundant appressed ground pilosity and erect clavate hairs of head and gastric apex, a few slender clavate hairs on the scutum, many on the gastric venter, and two irregular longitudinal groups of about 8 hairs each on each side of the gastric midline.

Type Material

Longino (2013) - Holotype queen: Brazil, Santa Catarina NMW? (not examined).

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 182, see also)
  • Emery, C. 1894d. Studi sulle formiche della fauna neotropica. VI-XVI. Bull. Soc. Entomol. Ital. 26: 137-241 (page 217, worker described)
  • 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
  • Mayr, G. 1887. Südamerikanische Formiciden. Verh. K-K. Zool.-Bot. Ges. Wien 37: 511-632 (page 580 , queen described)