Octostruma obtusidens

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Octostruma obtusidens
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Myrmicinae
Tribe: Attini
Genus: Octostruma
Species: O. obtusidens
Binomial name
Octostruma obtusidens
Longino, 2013

Octostruma obtusidens P casent0629827.jpg

Octostruma obtusidens D casent0629827.jpg

Specimen Label

Octostruma obtusidens is a moderately abundant lowland species. All Central American records are from sea level to 800 m. It occurs in mature to highly disturbed rainforest and in seasonal moist forest. Most collections are from Berlese and Winkler samples of sifted litter and rotten wood from the forest floor. In quantitative 1 m2 litter plot samples, it can occur in up to 11% of samples. Dealate queens are occasionally found together with workers in litter samples. One nest was observed at La Selva Biological Station in Costa Rica. A colony occurred in a 2–3 cm diameter nest in a soil cavity beneath a rotting palm trunk. The colony was polygynous, with at least 4 dealate queens. The nest contained an egg of Phasmatodea. (Longino 2013)

Identification

Face lacking transverse arcuate carina; basal five teeth of mandible bluntly rounded; face sculpture foveolate with at most faint longitudinal rugulae (longitudinally rugose on Octostruma excertirugis); ground pilosity curved, projecting from surface; first gastral tergite punctate over entire surface (punctate on anterior half, fading to nearly smooth and shining posteriorly on O. excertirugis). (Longino 2013)

Keys including this Species

Distribution

Latitudinal Distribution Pattern

Latitudinal Range: 17.1212917° to 8.783333333°.

 
North
Temperate
North
Subtropical
Tropical South
Subtropical
South
Temperate

Distribution based on Regional Taxon Lists

Neotropical Region: Colombia, Costa Rica (type locality), Guatemala, Honduras, Panama.

Distribution based on AntMaps

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Distribution based on AntWeb specimens

Check data from AntWeb

Countries Occupied

Number of countries occupied by this species based on AntWiki Regional Taxon Lists. In general, fewer countries occupied indicates a narrower range, while more countries indicates a more widespread species.
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Estimated Abundance

Relative abundance based on number of AntMaps records per species (this species within the purple bar). Fewer records (to the left) indicates a less abundant/encountered species while more records (to the right) indicates more abundant/encountered species.
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Biology

Explore-icon.png Explore Overview of Octostruma 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 Online Catalogue of the Ants of the World.

  • obtusidens. Octostruma obtusidens Longino, 2013: 44, figs. 1F, 3E, 4, 5F, 10B, 12A, 14E, 33, 43 (w.q.) COSTA RICA.

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

Description

Worker

HW 0.67-0.74, HL 0.62-0.64, WL 0.76-0.80, CI 104-116 (N=6). Labrum wider than long, strap-like lateral portions converging from base to near apex, joined by thin translucent cuticle medially but leaving distinctly bilobed apex, with distinct median notch; mandible triangular, in profile view with mandible closed, in same plane as clypeus, apex of mandible not down-turned; mandible with 8 teeth , tooth 1 continuous with basal rim of dorsal surface, teeth 1–5 bluntly rounded, similar in shape, a denticle between 4 and 5, teeth 6–7 smaller, not as blunt, tooth 8 long and acute; masticatory margin evenly curved, with no development of downturned apical fork; dorsal surface of mandible smooth and shining; ventral surface rounding into dorsal surface; scape flattened, with pronounced anterobasal lobe, dorsal surface roughened, microfoveolate; clypeus with broad, shallow emargination anteriorly; clypeal dorsum convex medially, clypeal suture impressed, forming shallow trough between clypeus and frons; clypeus and face densely foveolate, overlain with faint irregular rugulae; frontal carinae faint, nearly obsolete; antennal socket deep, dorsal rim of socket continuous with pronounced dorsal margin of antennal scrobe; antennal scrobe deep, pocket-like, strongly delimited dorsally, posteriorly, and ventrally with sharply defined laminar cuticular rim; compound eye small, circular, composed of about 7 ommatidia; feeble carina extends from ventral margin of antennal socket across floor of scrobe to compound eye; scrobe foveolate; occipital carina extends a short distance onto ventral surface of head, fading at level of compound eye; undersurface of head foveolate.

Promesonotum and dorsal face of propodeum forming an even convexity in profile, promesonotal suture not impressed, promesonotum with broad, weak, longitudinal impression; metanotal groove not impressed; propodeum with distinct dorsal and posterior faces meeting at a broadly obtuse angle; propodeal spines well-developed, acute, laterally flattened, internal surface concave, with dorsal margin of spine forming carina that curves medially but does not extend to midline, spine extending ventrally as thin infradental carina; irregular rugulae extend between propodeal spines, faint to absent medially, weakly separating dorsal and posterior faces of propodeum; propodeal spiracle large, diameter similar to width of base of propodeal spine, located below propodeal spine and abutting posterior margin; dorsum of promesonotum foveolate, overlain with weak rugulae; side of mesosoma and dorsal face of propodeum foveolate; posterior face of propodeum smooth, sublucid.

Petiole in profile with peduncle differentiated from node, node with differentiated anterior face; node subquadrate, with long sloping dorsal face and short vertical posterior face; anteroventral margin with pronounced, anteriorly-directed peg-like tooth; postpetiole low, broad, crescent-shaped in dorsal view; dorsum of petiolar node and postpetiole foveolate; first gastral tergite and sternite densely punctate.

Anterior labral lobe with radiating tuft of soft, thick, translucent, capitate setae of unequal length projecting from apex; each larger mandibular tooth with fully appressed seta running length of tooth; dorsal surface of scape, clypeus, face, promesonotal dorsum, legs, dorsal petiolar node, dorsal postpetiole, and first gastral tergite covered with conspicuous ground pilosity of small clavate setae that are strongly curved and projecting from the surface (not appressed), ground pilosity absent from side of mesosoma, dorsal and posterior propodeum; larger erect, brush-like spatulate setae conspicuous, anterior margin of scape with about 10, face with about 12, promesonotum with 4, apex of mesotibia with 5, petiolar node with 2, postpetiole with 2, first gastral tergite with 16 evenly distributed on tergite, first gastral sternite with 15–20 smaller clavate setae, more clustered posteriorly and medially.

Color orange.

Queen

HW 0.72–0.78, HL 0.68–0.71, WL 0.96–0.99, CI 102–113 (n=3). Mandible smooth and shiny; clypeus and face irregularly rugose, rugae somewhat longitudinally oriented on frons; antennal scrobe foveolate; ocelli distinct; compound eye large, multifaceted, about 12 ommatidia in longest row.

Mesosoma with queen-typical alar sclerites; anterior pronotum shallowly foveolate rugulose, lateral pronotum foveolate; mesoscutum and scutellum with weak foveolation overlain with prominent longitudinal rugulae; mesopleuron, metapleuron, and side of propodeum punctate; transverse mesopleural sulcus prominent, delimited above and below with a distinct carina; transverse metapleural sulcus delimited with an elliptical carina; dorsal face of propodeum foveolate rugulose, posterior face smooth; propodeal spines similar to worker; first gastral tergite and sternite punctate.

Ground pilosity thin and sparse, not clavate like worker; erect setae long and clavate, not spatulate and brush-like; face with about 22 erect setae, pronotum with 5–8, mesoscutum with 10–12, axilla with 1, scutellum with 2, metanotum with 2, petiolar node with 2, postpetiole with 6, first gastral tergite with 35–40.

Color orange to red orange, ocellar triangle darker brown.

Type Material

Holotype Specimen Labels

Holotype worker: COSTA RICA, Heredia: La Selva Biological Station, 10.43333, -84.01667, ±2 km, 50 m, 16 Mar 1993, wet forest, nest under dead wood (J. Longino#3390) Instituto Nacional de Biodiversidad, unique specimen identifier CASENT0629827. Paratype workers, queen: same data California Academy of Sciences, CASENT0627385; CASC, CASENT0629813; National Museum of Natural History, CASENT0629814; Museum of Comparative Zoology, CASENT0629815; Museu de Zoologia da Universidade de Sao Paulo, CASENT0629816; Colección de Artrópodos, CASENT0629817; Escuela Agricola Panamericana, CASENT0629818; Colección Entomológica de El Colegio de la Frontera Sur, CASENT0629819; University of California, Davis, CASENT0629820; CASC, CASENT0629821; CASC, CASENT0629822; CASC, CASENT0629823; CASC, CASENT0629824; CASC, CASENT0629825; John T. Longino Collection, CASENT0629826.

Etymology

The name refers to the blunt teeth on the mandible. It is a noun in apposition and thus invariant.

References

References based on Global Ant Biodiversity Informatics

  • Longino J. T. L., and M. G. Branstetter. 2018. The truncated bell: an enigmatic but pervasive elevational diversity pattern in Middle American ants. Ecography 41: 1-12.