Strumigenys opaca

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Strumigenys opaca
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Myrmicinae
Tribe: Attini
Genus: Strumigenys
Species: S. opaca
Binomial name
Strumigenys opaca
Brown, 1954

Strumigenys opaca casent0900920 p 1 high.jpg

Strumigenys opaca casent0900920 d 1 high.jpg

Specimen Labels

Known from rainforest litter-samples.

Identification

Bolton (2000) - A member of the Strumigenys wallacei-group. In the measurements small workers tend to have the mandibles and scapes relatively longer than large workers. The mandibles of opaca are relatively the longest found in the Austral region. The MI range of 57-63 in opaca contrasts with a range of MI 26-55 for all other Austral species together, of which only very few have MI > 50.

This species is closely related to the Malesian Strumigenys wallacei. The two are differentiate easily as in profile the mesonotum of wallacei forms a prominent hump or bulge, with a nearvertical posterior declivity; in opaca the mesonotum is more or less evenly rounded. In addition the ventral spongiform appendage of the postpetiole is a well developed lobe in wallacei, the first gastral sternite is less extensively sculptured (some shagreening is usually present near the base) and the scapes average shorter (SI 68-80).

Keys including this Species

Distribution

Distribution based on Regional Taxon Lists

Australasian Region: Australia (type locality).

Distribution based on AntMaps

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Distribution based on AntWeb specimens

Check data from AntWeb

Biology

Strumigenys were once thought to be rare. The development and increased use of litter sampling methods has led to the discovery of a tremendous diversity of species. Many species are specialized predators (e.g. see Strumigenys membranifera and Strumigenys louisianae). Collembola (springtails) and other tiny soil arthropods are typically favored prey. Species with long linear mandibles employ trap-jaws to sieze their stalked prey (see Dacetine trap-jaws). Larvae feed directly on insect prey brought to them by workers. Trophallaxis is rarely practiced. Most species live in the soil, leaf litter, decaying wood or opportunistically move into inhabitable cavities on or under the soil. Colonies are small, typically less than 100 individuals but in some species many hundreds. Moist warm habitats and micro-habitats are preferred. A few better known tramp and otherwise widely ranging species tolerate drier conditions. Foraging is often in the leaf litter and humus. Workers of many species rarely venture above ground or into exposed, open areas. Individuals are typically small, slow moving and cryptic in coloration. When disturbed individuals freeze and remain motionless. Males are not known for a large majority of species.

Castes

Nomenclature

The following information is derived from Barry Bolton's New General Catalogue, a catalogue of the world's ants.

  • opaca. Strumigenys opaca Brown, 1954a: 86 (w.) AUSTRALIA. See also: Bolton, 2000: 984.

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

Description

Worker

Holotype worker: TL 3.49 mm., HL 0.83 mm., ML 0.46 mm., WL 0.81 mm. CI 86, MI 55. Occipital lobes overlapping pronotum by about 0.04 m., this amount not subtracted from TL.

Head in outline very much as in Emery’s figure of Strumigenys wallacei, very broad and similarly deeply excised posteriorly: Eyes larger, more convex and more strongly protuberant, also more anteriorly directed, than those shown for wallacei in Emery’s figure. Actually, the eyes are situated on low protuberances, immediately in front of which run deep vertical preocular sulci; the latter continue onto the ventral surface of the head and join there to form the deep postoral sulcus. Antennal scrobes ending abruptly above the eyes. As the head is seen in direct dorsal view, the dorsolateral borders run well inside of the ventrolateral borders and are only very feebly indented at the level of the eyes. The periocular structure is similar to that of Strumigenys szalayi, Strumigenys nidifex, etc., but differs in having the dorsolateral borders only slightly indented above the eyes and in having the eyes themselves much larger and more protruding, more nearly prospicient.

Vertex evenly convex, 2eebly impressed in the middle; occipital lobes strongly depressed and nearly plane dorsally; broadly expanded both posteriad and laterad. Clypeus more than half again as broad as long, moderately convex, anterior border emarginate and weakly depressed in the middle.

Mandibles about as shown in Emery’s wallacei figure, slightly depressed and very slightly broadened just at their insertions. Seen from the side, they tilt slightly dorsad and are feebly arched. Apical fork of two long spiniform teeth, subparallel and forming a U, he ventral tooth (L 0.10 mm.) about 2/3 as long as the dorsal (L 0.15-0.16 mm.); no intercalary denticle. Preapical tooth slightly curved, spiniform, situated at approximately he apical third of the ML, its L ca. 0.10 mm.

Antennal scapes (straightline L about 0.60 mm.) very feebly bent posteriorly near the base, where they are very slender; apical half gradually incrassate, thickest at about the apical quarter, and gently arched so as to follow the contour of the sides of the head when in repose. This adaptation evidently compensates or he incomplete condition of the scrobes, and is seen in somewhat similar form in szalayi. Funiculus L 0.65 mm., the apical segment occupying just half this length; IV longer than I; II and III subequal, longer than broad, together not quite as long as I.

Anterior promesonotum gently convex, descending behind through the evenly concave posterior half of the mesonotum to the lower, extremely feebly convex (nearly straight in profile) propodeal dorsum; metanotal groove obsolete. Promesonotum seen from above with a very narrowly rounded and poorly developed anterior border; cervix with a median dorsal carinula. No traces of humeral angles or tubercles, humeral region gently convex, promesonotal suture obsolete. Propodeal teeth long (L ca. 0.12 mm.), set far apart, slender, acute, feebly diverging and elevated at an angle of about 35° from the plane of the propodeal dorsum. Infradental carinulae indistinct, becoming obsolete ventrad.

Petiolar peduncle slender, slightly longer than node. Node evenly rounded above, very slightly broader than long, with only very narrow, sublamellose vestiges of appendages posterodorsally, posterolaterally and ventrally. Postpetiole twice as broad as petiolar node, and higher and more bulky, subglobose, only slightly broader than long (L 0.20, W 0.25 mm.); spongiform appendages poorly developed, restricted to thin posterodorsal border and meager ventral and ventrolateral lobes.

Entire insect, except or shining mandibular apices, densely and finely sculptured and opaque; the sculpture predominantly punctulate as in other species of the genus, and similarly becoming more superficial and indistinct on the gastric dorsum, which, though largely quite opaque, becomes less definitely so toward the apex.

Dorsum of head, alitrunk and nodes with a sparse, inconspicuous ground pilosity of short, spatulate subappressed hairs. Clypeus with a medially directed fringe of spatulate hairs, about 9 or 10 on each side of the middle. Anterior border of scape with a regular row of stiff, apically-inclined oar-shaped hairs, becoming longer toward the scape apex; a similar row appears in Emery’s figure of wallacei, but the individual hairs in opaca appear to have broader blades apically. Hairs on inner mandibular borders near base long, fine, subreclinate; those near apex longer, perpendicular. Abundant short subreclinate hairs along posterior borders of scapes. No. specialized erect hairs on head or alitrunk. Short, erect, posteriorly-inclined clavo-spatulate hairs as follows: a pair on postpetiole; 3 pairs on basal gastric tergite; transverse rows of 4-6 hairs each on succeeding gastric segments, becoming smaller and finer toward extreme apex. Short fine hairs under gastric apex. Color deep brownish-red; mandibles, legs, antennae and occipital lobes a trifle lighter and more yellowish.

Paratypes: the remaining 14 workers from the type nest series are very uniform in structure and color, and quantitative variation is slight. TL 3.18-3.51, HE 0.78-0.85, ME 0.43-0.48, WE 0.75-0.8 ram.; CI 82-86, MI 54-57.

Bolton (2000) - TL 2.6-3.4, HL 0.70-0. 86, HW 0.57-0.78, CI 81-90, ML 0.44-0.52, MI 57-63, SL 0.50-0.64, SI 79-89, PW 0.30-0.37, AL 0.65-0.84 (20 measured).

Apical fork of mandible without intercalary denticles. In full-face view eyes completely visible, situated on a low tumulus and bounded anteriorly by the deep preocular notch. Scape shallowly sinuate in full-face view. Scrobe absent behind level of eye. Propodeal teeth free, subtended only by a narrow carina on each side of the declivity. Ventral spongiform strip on petiole slender, narrower than depth of peduncle. Postpetiole large and subglobular in profile. Ventral spongiform lobe on postpetiole a shallow rounded collar, the lateral lobe reduced to a thin flange except in the posterior corner where it is a little wider. Apicoscrobal hair absent; pronotal humeral hair absent. Dorsum of head and alitrunk with sparse spatulate ground-pilosity but without standing hairs. First gastral tergite with short stiff spatulate to remiform standing hairs. All surfaces of head, alitrunk, petiole and postpetiole finely densely reticulate-punctate, without smooth areas. First gastral tergite finely shagreenate-punctulate, the sculpture fading out posteriorly on the sclerite; without differentiated basigastral costulae or with costulae short and inconspicuous among the other sculpture. First gastral sternite finely reticulate-punctate at least basally and laterally, the mid-ventral area generally smooth or nearly so.

Type Material

Holotype Museum of Comparative Zoology selected from a nest series of 15 workers taken in rain-forest at Lankelly Creek in the McIlwraith Range, a few miles east of Coen, central Cape York Peninsula., Queensland during June, 1932 (P. J. Darlington: Harvard Australia Expedition).

Bolton (2000) - Holotype and paratype workers, AUSTRALIA: Queensland, Cape York Peninsula, McIlwraith Range, Lankelly Creek, vi.1932, Harvard Expd (P. J. Darlington) (Museum of Comparative Zoology, Queensland Museum, National Museum of Natural History, Naturhistorisches Museum Wien, Vienna) [examined].

References