Hypoponera opaciceps

A cryptobiotic species that forages in leaf mold. They are frequently found nesting in decaying wood.

Identification
The relatively coarse, subopaque body sculpture, the shape of the head and petiole are the main distinguishing features for this species (Kempf 1962).

The nearly parallel front and rear faces of the worker petiole (in lateral view) and non-shining integument, due to minute, dense granulation, distinguish this species. The male has very pale wing veins (almost transparent) and slightly elongate eyes. We have seen occasional ergatoid queens (or workers with large eyes).

Distribution
South Carolina through Florida, west to Colorado; Central and South America (as far south as Uruguay), West Indies, Southeast Asia and Polynesia (Smith 1979). Reported from Nevada by Wheeler and Wheeler (1986) and Arizona by Mackay and Mackay (2002). It was probably transported by commerce from the Neotropics to Pacific tropical areas (Wilson and Taylor 1967). It occurs in southern California in moist areas, such as the edges of irrigation ditches and low spots in watered lawns. Colonies have been found in the soil of potted plants in Florida, which is a center of the nursery trade. This species is also common along beaches in Florida; some of the early transportation of the species might have been in soil ballast obtained from beaches.

Distribution based on Regional Taxon Lists
Australasian Region: New Caledonia. Indo-Australian Region: American Samoa, Fiji, French Polynesia, Hawaii, Micronesia (Federated States of), New Guinea, Palau, Philippines, Samoa, Tonga. Nearctic Region: United States. Neotropical Region: Argentina, Bahamas, Barbados, Bermuda, Brazil, Costa Rica, Cuba, Dominican Republic, Ecuador, Galapagos Islands, Guatemala, Guyana, Haiti, Lesser Antilles, Mexico, Panama, Paraguay, Peru, Puerto Rico, Trinidad and Tobago, Uruguay. Palaearctic Region: China, Japan.

Biology
Smith (1929) reports on a nest being taken from a partly decayed pine stump (Ocean Springs, MS). Deyrup, Davis and Cover (unpublished) noted this ant in Florida: "forms small colonies in open or partially shaded areas. Most common in wet or periodically flooded areas, where it tends to replace Hypoponera opacior in fallen logs, grass tussocks and accumulations of organic matter (see Van Pelt 1958, excerpt below). It sometimes occurs under piles of seaweed high up on the beach. This species is a rapid colonizer of disturbed areas such as lawns and ditches. In southern Florida alates may be found in flight in the afternoon and evening at any time of the year. Alate queens can deliver a noticeable sting when they become trapped under clothing or stuck to the skin by sweat.

Van Pelt (1958), reporting on this species within the Weleka Reserve in Florida: "Many of the nests of opaciceps, especially in marsh, contained one to several individuals which are evidently aberrant workers, These insects have large compound eyes, comparable to those of the queen, and the petiole is, more slender than that of the normal worker. It is perhaps significant that queens were not found in nests which contained these aberrant forms.

This species prefers the wet or flooded areas of the Reserve, and tends to replace P. trigona opacior (=Hypoponera opacior), a form which prefers high, dry areas. It has been taken abundantly in marsh; commonly in hydric hammock and river swamp; and rarely in Rutledge slash pine flatwoods, bayhead, and xeric hammock. In the Gainesville region, P. opaciceps was taken in longleaf pine flatwoods where there are more fallen logs than in the same plant association on the Reserve. It ought to occur also in at least the lower portions of mesic hammock.

Most often this ant nests in the bases of sawgrass plants between the appressed leaves. Many times the ant can be found in the wet or saturated moss-covered stumps of the plants where there is an intermingling of roots in the decomposing, appressed leaves and wet debris. The other nesting sites, in order of preference, are: 1) fallen logs, 2) dead stumps, 3) bases of living trees (under moss and litter at water surface), 4) in litter (wet), 5) palmetto roots on ground, 6) under mat of palmetto roots, and 7) under mat of palmetto trunks. In general, the nests are wet to saturated and built in debris. Most of the nests, especially those in sawgrass, are at the water surface, or just above or below it. (In this latter case, the tight growth of the plant parts seems to keep the water from the nest.) In situations which are less wet, the insect continues to simulate the above-mentioned nesting conditions in its choice of wet pulpy wood of logs, or the debris found under the bark of logs or stumps.

Of 5 nests counted, the number of workers varied from 15 to 84, with an average of 40 per nest. Each of these nests contained from one to three of the aberrant workers described above, and none contained a queen. Immature forms probably occur in all months, but from September through November very few were noticed in the nests. Females are produced from September to November, and males from October to November.

This is a fast moving and evasive ant which blends with the color of its surroundings. It is much less active in winter months, although this is the period winged forms are in the nest."

New Mexico
Mackay and Mackay (2002) - Habitat. Cottonwood-willow forests, riparian habitats and sagebrush, urban areas. Biology. This ant nests under stones. The specimens in Albuquerque were collected on sandbars along the Rio Grande river in pitfall traps (Fagerlund, pers. comm.).

Nomenclature

 *  opaciceps. Ponera opaciceps Mayr, 1887: 536 (w.q.) BRAZIL. Smith, M.R. 1929: 545 (m.); Wheeler, G.C. & Wheeler, J. 1964b: 453 (l.). Combination in Hypoponera: Taylor, 1967a: 11. Senior synonym of perkinsi (and its junior synonym andrei): Wilson & Taylor, 1967: 28; of postangustata: Wild, 2007b: 54. Current subspecies: nominal plus cubana, gaigei, jamaicensis, pampana,. See also: Smith, M.R. 1936: 428; Wheeler, W.M. 1937c: 59; Kempf, 1962b: 7.
 * andrei. Ponera andrei Emery, 1900c: 318 (footnote), pl. 8, fig. 47 (w.) NEW CALEDONIA. Junior synonym of perkinsi: Wilson, 1958d: 334.
 * perkinsi. Ponera perkinsi Forel, 1899a: 117 (w.q.m.) HAWAII. Senior synonym of andrei: Wilson, 1958d: 334. Junior synonym of opaciceps: Wilson & Taylor, 1967: 28. See also: Wheeler, W.M. 1909c: 271.
 * postangustata. Ponera opaciceps var. postangustata Forel, 1908c: 343 (w.) PARAGUAY. Combination in Hypoponera: Kempf, 1972a: 123. Junior synonym of opaciceps: Wild, 2007b: 54.

Taxonomic Notes
This species has a number of subspecies, named during a period when ants from widely separated areas were often assumed (usually correctly) to be different species or subspecies. In this case, since H. opaciceps seems to be readily transported by humans, it is likely that most of these far-flung subspecies are either trivial, non-geographic variants, or different species.

Worker
Smith (1936) - Length: 3.2-3.4 mm. Head, excluding mandibles, longer than broad, posterior border faintly emarginate, the sides convex, and the posterior angles rounded. Eyes small, with approximately 10-12 facets, situated at a distance less than twice their greatest diameter from the base of the mandibles. Mandibles with more irregular teeth than with Ponera pennsylvanica, the front teeth not only larger but more regular. Clypeus convex medianly. No frontal area. A faint frontal furrow extends half the distance or beyond from the frontal carinae to the posterior border of the head. Scape not attaining the posterior border of the head; the funiculus clavate, the last segment apparently shorter than the three preceding segments. Thorax with distinct promesonotal and meso-epinotal sutures, not so laterally compressed, especially about the epinotum as with P. pennsylvanica; epinotal declivity faintly concave, with bluntly marginate sides, meeting the base in a well rounded, obtuse angle. Petiole viewed in lateral profile thick antero-posteriorly, scarcely narrower dorsally, convex anteriorly, concave posteriorly; viewed posteriorly the superior border merges into the sides in well rounded angles; tooth below although rectangular, apparently lacking the spiracular opening in front, and the point posteriorly, as with P. pennsylvanica.

Head, thorax, petiole, and gaster very densely and finely punctate, subopaque; meso- and meta-pleurae finely and longitudinally striated; mandibles, and epinotal declivity rather smooth and shining.

Pubescence yellowish gray, dense and appressed, covering all parts of the body. Hairs grayish, very noticeable on the clypeus and gaster where they are longest and most abundant; usually found sparingly on other parts of the body.

Color varying from brown to black; mandibles, antennal funiculi, legs and tip of gaster lighter.

Queen
Smith (1936) - Length: 3.7-4 mm. So similar to the worker as to hardly warrant a brief description. Very slightly larger. Compound eyes placed at a distance from the mandibles less than their greatest diameter. Frontal furrow extending to the anterior ocellus. Petiole proportionally smaller and narrower anteroposteriorly on the dorsal border than with the worker. Wings very hyaline, with light yellowish veins and stigma, each with a submarginal and discoidal cell.

Smith (1936) - Ergataner. - Length of head .68-.76 mm.; length of thorax .935-.965 mm. Head, including mandibles, longer than broad; posterior border almost straight, and sides subparallel, thus giving the head a more rectangular appearance than with the worker. Mandibles moderately broad, triangular, edentate stubs. Clypeus strongly convex, protuberant. Antennae 13-segmented, gradually but not strongly enlarging distally; scapes short, subcylindrical, approximately equal in length to the second, third, and fourth segments of the funiculi taken together. Compound eyes small, almost circular, separated from the base of the mandibles by a space equivalent to approximately one and one-half times their greatest diameter. Thorax short, robust; viewed laterally the pro-mesonotal and meso-epinotal sutures are very distinct, especially on the dorsum; mesonotum strongly gibbous, clearly projecting above the general surfaces of the pronotum and epinotum. Between the mesonotum and epinotum the suture is represented by a very strong constriction, following which, the epinotum forms a rather long and gentle arch terminating at the petiole. The basal surface and declivity of the epinotum merge into each other so gradually that they are hardly distinguishable. Petiole large, robust, anterior and posterior faces convex, superior border rounded. Gaster similar to that of the worker, but bearing prominent genital appendages.

Color sordid yellow; margins of compound eyes and antennal cavities black, articulations of legs and sutures of thorax brown.

The above description is based on two specimens which were taken from a colony of Ponera opaciceps at Landon, Mississippi, by G. W. Haug on August 25, 1930. No other ergataners of this species have been seen or recorded.

Type Material
Reported by Smith (1936) - Province of Saint Catherine, Brazil (Mayr). Kempf (1962) states he examined 4 type specimens sent to him from the.

Etymology
opacus  - shady, dark, dim + ceps - head.