Octostruma trithrix

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

In the southern portion of its range, Octostruma trithrix occurs in a variety of forested habitats: wet to seasonal dry, second growth to mature. It is typically lowland, occurring from sea level to around 700 m. In the northern part of the range it occurs in cloud forest, up to 1200 m elevation. Almost 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, within-sample abundance is tens of workers or fewer, but the species can occur frequently, suggesting a high density of small colonies. Dealate queens may occur together with workers in litter samples. (Longino 2013)

Identification

Longino (2013) - Mandible with 8 teeth, tooth 1 a broad blunt lamella, strongly differentiated from tooth 2, teeth 2–5 acute, similar in shape, with denticles between them; teeth 5–8 forming an apical fork, with 5 and 8 large, 6 and 7 small partially confluent denticles (O. balzani complex); face setation, erect setae present on posterolateral margins of head (absent in Octostruma amrishi and Octostruma gymnogon); in most workers of a series, a seta present between anterior seta on side of head near eye and medial vertex seta (this seta typically absent in Octostruma balzani, O. megabalzani, O. amrishi, and O. gymnogon); mesosomal dorsum with one pair of erect setae (absent in O. amrishi, O. gymnogon; 2 pairs in Octostruma lutzi); metanotal groove not impressed in profile view (impressed in O. balzani and O. megabalzani).

Keys including this Species

• Key to Octostruma species

Distribution

Northern Mexico (Nuevo Leon) to Honduras.

Latitudinal Distribution Pattern

Latitudinal Range: 25.189293° to 15.5123738°.

North Temperate	North Subtropical	Tropical	South Subtropical	South Temperate

• Source: AntMaps

Distribution based on Regional Taxon Lists

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

Distribution based on AntMaps

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.

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.

Biology

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. ‎

Nomenclature

The following information is derived from Barry Bolton's Online Catalogue of the Ants of the World.

• trithrix. Octostruma trithrix Longino, 2013: 54, figs. 1E, 3D, 5A, 8A, 40, 42 (w.q.) MEXICO.

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

Description

Worker

HW 0.54–0.62, HL 0.50–0.58, WL 0.52–0.66, CI 102–112 (n=7). Matching in almost every respect the description for Octostruma balzani, except the differences outlined in the Diagnosis and key. In addition to characters in the Diagnosis, first gastral tergite typically with 8–16 erect setae, color red brown.

Queen

HW 0.59–0.64, HL 0.55–0.60, WL 0.70–0.75, CI 103–107 (n=7). Similar to O. balzani in most respects; 4–6 setae across vertex between compound eyes (2–4 in O. balzani); postpetiolar disc with 4–6 erect setae (2–4 in O. balzani).

Type Material

Holotype Specimen Labels

Holotype worker: Mexico, Chiapas: 8 km SE Salto de Agua, 17.51611, -92.30168, ±50 m, 100 m, 14 Jun 2008, 2º wet forest, ex sifted leaf litter (LLAMA, Wa-A-08-2-03) California Academy of Sciences, CASENT0639179. Paratype workers, queen: same data University of California, Davis, CASENT0639180; Colección de Artrópodos, CASENT0639181; Escuela Agricola Panamericana, CASENT0639182; CASC, CASENT0639183; John T. Longino Collection, CASENT0639184; same data except 17.51442, -92.29500, ±50 m, 70 m (LLAMA, Wa-A-08-1-05) Colección Entomológica de El Colegio de la Frontera Sur, CASENT0639174; National Museum of Natural History, CASENT0639175; Museum of Comparative Zoology, CASENT0639176; Museu de Zoologia da Universidade de Sao Paulo, CASENT0639177; CASC, CASENT0639178.

Etymology

The name refers to anterior row of three spatulate setae on the face. It is a noun in apposition and thus invariant.

References

• Ahuatzin, D.A., González-Tokman, D., Valenzuela-González, J.E., Escobar, F., Ribeiro, M.C., Acosta, J.C.L., Dáttilo, W. 2021. Sampling bias in multiscale ant diversity responses to landscape composition in a human-disturbed rainforest. Insectes Sociaux (doi:10.1007/s00040-021-00844-2).
• 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

References based on Global Ant Biodiversity Informatics

• Ahuatzin D. A., E. J. Corro, A. Aguirre Jaimes, J. E. Valenzuela Gonzalez, R. Machado Feitosa, M. Cezar Ribeiro, J. Carlos Lopez Acosta, R. Coates, W. Dattilo. 2019. Forest cover drives leaf litter ant diversity in primary rainforest remnants within human-modified tropical landscapes. Biodiversity and Conservation 28(5): 1091-1107.
• Dattilo W. et al. 2019. MEXICO ANTS: incidence and abundance along the Nearctic-Neotropical interface. Ecology https://doi.org/10.1002/ecy.2944
• 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.
• Longino J. et al. ADMAC project. Accessed on March 24th 2017 at https://sites.google.com/site/admacsite/