Octostruma rugiferoides

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Octostruma rugiferoides
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Myrmicinae
Tribe: Attini
Genus: Octostruma
Species: O. rugiferoides
Binomial name
Octostruma rugiferoides
Brown & Kempf, 1960

MCZ-ENT00030880 Octostruma rugiferoides hal.jpg

MCZ-ENT00030880 Octostruma rugiferoides had.jpg

Specimen Label

The types were collected by E. O. Wilson in leaf litter of dry, rocky, tropical evergreen forest. New material collected by the LLAMA project was in scrubby wet forest of eastern Chiapas and the seasonal evergreen forests of the Tikal region in Guatemala. All specimens were from Winkler samples of sifted leaf litter from the forest floor. (Longino 2013)

Identification

Keys including this Species

Distribution

Distribution based on Regional Taxon Lists

Neotropical Region: Guatemala, Mexico (type locality), Mexico (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.

  • rugiferoides. Octostruma rugiferoides Brown & Kempf, 1960: 200, fig. 20 (w.) MEXICO.

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

Description

Worker

Holotype: TL 2.0, HL 0.53, HW 0.55 (CI 104), ML 0.13, WL 0.52 mm. Closely resembles small workers of Octostruma rugifera, but the blunt lateral angles behind the eye are reduced and ventrally displaced, so as not to be visible from full-face dorsal view; mandibles also slightly shorter. The following additional differences are noted:

1. Head and promesonotum with rugulo-reticulum overlying punctulation; concave portion of head anterior to transverse arcuate carina (including clypeus) irregularly rugulose, with a fine median longitudinal carina, weakly shining, except the posterior lobe of the clypeus and the median frontal region just behind it, which are smooth and shining. Mandibles smooth and shining. Body otherwise densely granulose-punctulate and opaque, except for the weakly shining posterior half of gaster.

2. Metanotal groove nearly or quite obsolete on the dorsum, rendering the dorsal profile in side view rather even in transition from the mesonotum into the gently sloping propodeal dorsum.

3. Petiolar node seen from side more narrowly rounded over summit.

4. Erect hairs lacking on alitrunk and both nodes; 2-3 spatulate ones at tibial apices. First gastric tergite with only a single transverse row of 4 erect clavate hairs near its posterior margin, although numerous minute, curved, reclinate ground hairs are somewhat more abundant and conspicuous over this tergite than in O. rugifera.

Longino (2013) - The description of Brown and Kempf is supplemented with these new measurements: HW 0.54–0.57, HL 0.53–0.54, WL 0.52–0.55, CI 103–105 (n=3).

Queen

Longino (2013) - HW 0.59, HL 0.57, WL 0.68, CI 103 (n=1). Posterior margin of head evenly rounded; labrum, mandible, anterior clypeal margin, scape, antennal scrobe similar to worker; clypeus smooth, delimited from frons by faint clypeal suture; concave frons anterior to facial arc sublucid, very faintly rugulose; facial arc crenulate; sculpture posterior to arc irregularly rugulose, like worker; face with 10 erect setae distributed evenly on facial arc, 6 setae on posterior margin of head; ocelli distinct; compound eye multifaceted, about 6 ommatidia in longest row.

Mesosoma with queen-typical alar sclerites; pronotum mostly foveolate, with a few rugulae on humeri; mesoscutum and scutellum with faint foveolation overlain by irregular longitudinal rugae; anepisternum and katepisternum separated by strong sulcus; mesopleuron and side of propodeum foveolate; posterodorsal propodeum forming a single concave face, faintly foveolate; propodeal spines low, obtuse, laminar, continuous with an infradental lamella; on single available queen, pronotum with 2 erect setae, mesoscutum with 6, axilla with 1, scutellum with 2, postpetiole with 3, first gastral tergite with about 24.

Type Material

Holotype worker: Mexico, Veracruz: Pueblo Nuevo, near Tetzonapa, 13 Aug 1953, in leaf litter of dry, rocky, tropical evergreen forest (E. O. Wilson) Museum of Comparative Zoology] (examined); paratype worker: same data as holotype but 7 Aug 1953 Museu de Zoologia da Universidade de Sao Paulo.

Determination Clarification

Longino (2013) - Palacio (1997) reports Octostruma rugiferoides for Colombia, but clearly meant Octostruma rugifera, because he describes the species as occurring in Brazil and Argentina, and gives the author as (Mayr 1887).

References

  • Brown, W. L., Jr.; Kempf, W. W. 1960. A world revision of the ant tribe Basicerotini. Stud. Entomol. (n.s.) 3: 161-250 (page 200, fig. 20 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