Octostruma wheeleri

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Octostruma wheeleri
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Myrmicinae
Tribe: Attini
Genus: Octostruma
Species: O. wheeleri
Binomial name
Octostruma wheeleri
(Mann, 1922)

Octostruma wheeleri P casent0280764.jpg

Octostruma wheeleri D casent0280764.jpg

Specimen Label

Octostruma wheeleri occurs in lowland rainforest, seasonal moist forest, and occasionally in cloud forest habitats. It occurs from sea level to 1100 m elevation, with greatest abundance below 600 m (up to 16% of 1 m2 plot litter samples in quantitative sampling). It is only known from Winkler and Berlese samples of sifted leaf litter. (Longino 2013)

Identification

Keys including this Species

Distribution

Distribution based on Regional Taxon Lists

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

Distribution based on AntMaps

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Distribution based on AntWeb specimens

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Biology

Longino (2013) - Quantitative sampling in Chiapas revealed a sharp parapatric distribution with the highland Octostruma triangulabrum, with a narrow zone of sympatry around 1000 m elevation. At three lowland sites in Chiapas, O. wheeleri occurred in 12%, 11%, and 12% of 100 plot samples, and O. triangulabrum was absent. At Nahá, at 980 m elevation and only 20 km away from one of the lowland sites (Laguna Metzabok at 570 m elevation), O. triangulabrum occurred in 13% of samples and a single O. wheeleri specimen was found.

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.

  • wheeleri. Rhopalothrix (Octostruma) wheeleri Mann, 1922: 43 (w.) GUATEMALA. Combination in Octostruma: Brown, 1949f: 92. See also: Brown & Kempf, 1960: 191.

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

Longino (2013) - Specimens from Chiapas to Honduras are uniform with respect to face setae. A worker from Las Marias in eastern Honduras is lacking the posteriomedian pair. The single worker from Hitoy Cerere, Costa Rica, has a single posteromedian pair, lacking the lateral and ocular setae.

Description

Worker

Longino (2013) - HW 0.69–0.85, HL 0.63–0.75, WL 0.75–1.05, CI 108–114 (n=10). Labrum sides straight, strap-like lateral portions converging from base to apex, fused apically (not bilobed, at most with minute notch apically), joined medially by thin translucent cuticle; mandible triangular, in profile view with mandible closed, in same plane as clypeus, apex of mandible not down-turned; mandible with 8 teeth, basal rim of dorsal surface slightly offset from base of tooth 1, forming small denticle, teeth 1–5 acute, similar in shape, teeth 5–8 forming an apical fork, with 5 and 8 large, 6 and 7 small partially confluent denticles; dorsal surface of mandible roughened; ventral surface flat and parallel to clypeus apically, twisting basally to nearly perpendicular orientation basally, smooth and shining; interior surface concave, smooth and shining; scape flattened, with pronounced anterobasal lobe, dorsal surface roughened, dull; clypeus with broad, shallow emargination anteriorly; clypeus and face sculpture varying from almost completely smooth to very shallowly, irregularly rugulose, generally matte; frontal carinae faint, nearly obsolete; antennal socket deep, dorsal rim of socket continuous with pronounced dorsal margin of antennal scrobe; antennal scrobe deep, strongly delimited dorsally, posteriorly, and ventrally with sharply defined thin cuticular rim; compound eye small, circular, composed of about 7 ommatidia; distinct carina extends from ventral margin of antennal socket across floor of scrobe to compound eye; scrobe floor faintly foveolate, matte; vertex margin anterior to occipital carina smooth, sublucid (top of head, not visible in face view); occipital carina extends anteriorly on ventral surface of head to level of compound eye; undersurface of head rugulose.

Promesonotum convex in profile, promesonotal suture not impressed; metanotal groove not impressed; propodeum with distinct dorsal and posterior faces; dorsal face weakly convex; propodeal spines well-developed, in the form of acute flattened perpendicular plates, extending ventrally as thin carinae; single well-defined transverse carina extends between propodeal spines, separating dorsal and posterior faces of propodeum; propodeal spiracle medium-size, diameter less than width of base of propodeal spine, located below propodeal spine and abutting posterior margin; most surfaces of mesosoma matte, dorsal face of propodeum sublucid, posterior face shining; dorsum of promesonotum with sculpture similar to face, dorsal and posterior face of propodeum smooth, lateral pronotum smooth; meso-metapleuron and side of propodeum confluent, smooth.

Petiole in profile with peduncle differentiated from node, node with differentiated anterior face; node triangular, with long sloping dorsal face; anteroventral margin with peg-like tooth; postpetiole low, broad, crescent-shaped in dorsal view; dorsum of petiolar node and postpetiole shallowly rugulose, matte; first gastral tergite densely punctate, interspaces sublucid; first gastral sternite uniformly 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; anterior margin of scape with about 8 stiff clavate setae; clypeus and face with fine, sparse fully appressed ground pilosity; face typically with 6 erect clavate setae; mesosomal dorsum lacking erect setae; mesotibia with about 5 clavate seta of variable length at apex; petiole, postpetiole, first gastral tergite lacking erect setae; ground pilosity of first gastral tergite short, sparse, fully appressed; first gastral sternite with abundant clavate setae clustered on posterior half, anterior half devoid of setae.

Color dark brown.

Queen

Longino (2013) - HW 0.86, HL 0.75, WL 1.06, CI 115 (n=1).Labrum, mandible, scape, antennal scrobe similar to worker; clypeus and face shallowly irregularly rugulose, tops of rugulae sublucid; face with one pair erect setae in front of eyes, one pair on posterolateral margin, one pair on posteromedian margin, one pair on medial frons (8 total); ocelli distinct; compound eye large, multifaceted, about 12 ommatidia in longest row.

Mesosoma with queen-typical alar sclerites; pronotum matte, faintly and sparsely punctate anteriorly and laterally, coarsely rugulose on humeri; mesoscutum, scutellum, dorsal face propodeum coarsely longitudinally rugose; anepisternum and katepisternum separated by strong sulcus; anepisternum, katepisternum, and side of propodeum matte, smooth; propodeal spines triangular, acute; pronotum with 2 erect setae, mesoscutum with about 12, axilla with 1, scutellum with 2, metanotum with 2, petiolar node with 2, postpetiolar disc with 2, first gastral tergite with about 25. Other characters similar to worker.

Type Material

Holotype worker: Guatemala, Livingston (Barber & Schwarz) National Museum of Natural History (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 191, see also)
  • 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
  • Mann, W. M. 1922. Ants from Honduras and Guatemala. Proc. U. S. Natl. Mus. 61: 1-54 (page 43, worker described)