Octostruma excertirugis

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

Octostruma excertirugis P casent0629828.jpg

Octostruma excertirugis D casent0629828.jpg

Specimen Label

Octostruma excertirugis is a moderately abundant lowland species from Mexico to Costa Rica. All records are from sea level to 800 m. It occurs in mature to highly disturbed rainforest and in seasonal moist forest. All 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 16% of samples and is as or more abundant in second growth forest than in mature forest. Dealate queens are occasionally found together with workers in litter samples. (Longino 2013)

Identification

Face lacking transverse arcuate carina; basal five teeth of mandible bluntly rounded; face sculpture longitudinally rugose; ground pilosity fully appressed; first gastral tergite punctate on anterior half, fading to nearly smooth and shining posteriorly. (Longino 2013)

Keys including this Species

Distribution

Distribution based on Regional Taxon Lists

Neotropical Region: Belize, Costa Rica, Ecuador, Guatemala (type locality), Honduras, Mexico, Panama.


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.

  • excertirugis. Octostruma excertirugis Longino, 2013: 30, figs. 1F, 3E, 5G, 12B, 14F, 23, 43 (w.q.) GUATEMALA.

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

Description

Worker

HW 0.57–0.66, HL 0.55–0.63, WL 0.64–0.77, CI 103–110 (n=15). 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 minute 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 punctate; ventral surface concave, twisting toward articulation, broad basally and narrowing abruptly to narrow apical half to third; scape flattened, with pronounced anterobasal lobe, dorsal surface somewhat roughened; clypeus with broad, shallow emargination anteriorly; clypeus and face irregularly longitudinally rugose; 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 thin 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; at about midlength on ventral margin of scrobe a variably-developed short carina extends perpendicularly onto floor of scrobe; ventral half of scrobe floor anterior to this short carina shallowly foveolate, rest of scrobe floor smooth, matte; vertex margin anterior to occipital carina densely punctulate, matte (top of head, not visible in face view); occipital carina extends a short distance onto ventral surface of head, fading before reaching level of compound eye; undersurface of head rugulose.

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, in the form of right-angled flat translucent perpendicular plates, extending ventrally as thin carinae; 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; all surfaces of mesosoma matte; dorsum of promesonotum irregularly rugose, dorsal face of propodeum faintly punctate, posterior face of propodeum smooth, lateral pronotum punctate; dorsolateral propodeum punctate, lower propodeum and mesopleuron confluent and smooth.

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 punctate; first gastral tergite and sternite anteriorly with dense, confluent puncta, on disc puncta are sparse with smooth shiny interspaces, on posterior margin puncta are more dense but smaller than anterior puncta and not confluent.

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; anterior margin of scape with about 11 spatulate setae; clypeus and face with fine, sparse fully appressed ground pilosity; face typically with 10 erect spatulate setae; pronotum with one pair erect setae on humeri; mesonotum with a pair of erect spatulate setae; mesotibia with conspicuous spatulate ground pilosity, about 5 short spatulate setae of variable length at apex; petiole with 2 erect setae; postpetiole with 2 erect setae; first gastral tergite with 2 spatulate setae at posterior margin, 2–6 (usually 2) setae on disc, ground pilosity fully appressed, sparse (length of setae less than distance between them); first gastral sternites with abundant short clavate to spatulate setae on posterior half to two thirds of sternites.

Color red brown.

Queen

HW 0.58–0.64, HL 0.61–0.65, WL 0.81–0.90, CI 95–101 (n=5). Labrum, mandible, scape, and head sculpture similar to worker; antennal scrobe floor entirely smooth and matte; face with about 8 erect setae distributed as in worker, plus 2–6 on central frons, anterior to lateral ocelli; ocelli distinct; compound eye large, multifaceted, about 12 ommatidia in longest row.

Mesosoma with queen-typical alar sclerites; pronotum shallowly rugulose anteriorly, with dense confluent puncta laterally; mesoscutum, axilla, and scutellum shallowly longitudinally rugulose; anepisternum and katepisternum separated by strong sulcus; anepisternum, katepisternum, and most of side of propodeum with dense confluent puncta, with smooth matte patch in center of lower side of propodeum; dorsal face of propodeum faintly punctate; posterior face of propodeum smooth and shining dorsally, faintly foveolate ventrally; propodeal spines similar to worker; first gastral tergite and sternite with relatively uniform puncta, interspaces subequal in width to puncta, smooth and shining; pronotum with 2–4 erect setae, mesoscutum with 2–6, axilla, scutellum, and metanotum lacking erect setae, petiolar node with 2, postpetiolar disc with 2, first gastral tergite with about 10. Other characters similar to worker.

Type Material

Holotype Specimen Labels

Holotype worker: GUATEMALA, Izabal: 5 km NW Morales, 15.51465, -88.86440, ±28 m, 280 m,18 May 2009, 2º lowland rainforest, ex sifted leaf litter (LLAMA, Wm-B-04-1-09) California Academy of Sciences, unique specimen identifier CASENT0629828]. Paratype workers, queen: same data Escuela Agricola Panamericana, CASENT0629829; Colección Entomológica de El Colegio de la Frontera Sur, CASENT0629830; CASC, CASENT0629831; John T. Longino Collection, CASENT0629832; same data except 15.51430, -88.86479, ±50 m, 250 m, 17 May 2009 (LLAMA, Wa-B-04-2-36) National Museum of Natural History, CASENT0610160; Museum of Comparative Zoology, CASENT0610161; 15.51351, -88.86647, ±26 m, 245 m (LLAMA, Wm-B-04-1-01) Colección de Artrópodos, CASENT0611289; Instituto Nacional de Biodiversidad, CASENT0611290; Museu de Zoologia da Universidade de Sao Paulo, CASENT0611291.

Etymology

The name refers to the pronounced rugae on the face, that often project through the soil layer. It is a dative plural noun and thus invariant.

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