Octostruma megabalzani

Every Ant Tells a Story - And Scientists Explain Their Stories Here
Jump to navigation Jump to search
Octostruma megabalzani
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Myrmicinae
Tribe: Attini
Genus: Octostruma
Species: O. megabalzani
Binomial name
Octostruma megabalzani
Longino, 2013

Octostruma megabalzani P mcz-ent00511006.jpg

Octostruma megabalzani D mcz-ent00511006.jpg

Specimen Label

Octostruma megabalzani is a montane species. The lowest elevation record is 950 m in Panama, and the highest record is 2000 m in southern Peru. It has been collected most often in mature cloud forest and montane oak forest habitats, but has also been collected in litter beneath cultivated coffee. All collections are from Berlese and Winkler samples of sifted litter and rotten wood from the forest floor. (Longino 2013)

Identification

Differing from Octostruma balzani as follows (O. balzani characters in parentheses): petiole with a pair of erect setae (typically lacking); postpetiole with 2–4 erect setae (0–2); first gastral tergite with 16–22 erect setae, more or less evenly distributed on tergite, gastral setae stiff, flattened, but nearly linear, very weakly clavate (first gastral tergite with 4–16 erect setae, these clustered posteriorly, relatively more broadened apically); color dark brown (red brown); HW 0.61–0.66 (HW 0.50–0.63). (Longino 2013)

Keys including this Species

Distribution

Distribution based on Regional Taxon Lists

Neotropical Region: Bolivia, Panama (type locality), Peru.


Distribution based on AntMaps

AntMapLegend.png

Distribution based on AntWeb specimens

Check data from AntWeb

Biology

The Andean and Central American specimens of O. megabalzani appear identical. Both occur in elevational parapatry with lowland Octostruma balzani. Whether the Andean and Central American populations are members of one montane clade or convergently evolved montane forms is an open question.

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.

  • megabalzani. Octostruma megabalzani Longino, 2013: 42, figs. 1E, 3D, 5B, 9B, 31, 42 (w.q.) 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 0.61–0.66, HL 0.56–0.61, WL 0.60–0.66, CI 107–111 (n=7). Similar in most respects to Octostruma balzani except for the characters in the diagnosis (see the identification section above).

Queen

HW 0.67, HL 0.62, WL 0.84, CI 108 (n=1). Labrum, mandible, scape, antennal scrobe, and head sculpture similar to worker; face with 8 erect setae distributed symmetrically around lateral and posterior margins of head, a seta on low ridge in front of each compound eye, 6 setae across vertex between compound eyes; ocelli distinct; compound eye large, multifaceted, about 12 ommatidia in longest row.

Mesosoma with queen-typical alar sclerites; sculpture like workers; anepisternum and katepisternum separated by strong sulcus; posterodorsal propodeum concave; propodeal spines pronounced, in the form of flattened perpendicular plates, acute in profile; pronotum with 4 erect setae, mesoscutum with 10, axilla with 1, scutellum with 2, metanotum with 2, petiolar node with 2, postpetiole and gaster missing from single queen available for examination. Other characters similar to worker.

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-ENT00511006]. Paratype queen, worker: same data MCZ, MCZ-ENT00511004; National Museum of Natural History, MCZ-ENT00511005.

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