Anochetus inermis

Brown, WL Jr.,, 1978, Contributions toward a reclassification of the Formicidae. Part VI. Ponerinae, tribe Ponerini, subtribe Odontomachiti. Section B. Genus Anochetus and bibliography., Studia Entomologica 20, pp. 549-638 : 613-617

[40] A. inermis

is found in its «typical» form in Trinidad and the Lesser Antilles (Martinique, Grenada, St. Vincent), and is known from widely separated localities in the Venezuelan llanos. Samples from the Guajira Peninsula, Cartagena and near Santa Marta, Colombia, indicate a range extending much farther west into the northern lowlands of Colombia. This form is a nearly uniform tawny to yellowish-red in color, with the forebody prevailingly opaque, especially the trunk, which is densely punctulate. The eyes are large (greatest diameter 0.20-0.24 mm), the propodeal teeth or angles are low and obtuse, and the upper edge of the petiolar node is only weakly emarginate, with bluntly angulate or even rounded corners (fig. 43) as seen from in front.

The mandibles are gradually enlarged from the base toward the apex until the inside preapical angle; the ventral of the two inner margins is furnished with 1-7 low, irregular teeth, denticles or serrations, increasingly coarse apicad. In some specimens, the denticulation is not developed, and the preapical masticatory border may appear edentate, particularly when the mandibles are completely closed. This mandibular variation is due partly to wear and partly to congenital differences among individual adults and populations

(fig- 6)..

The gastric dorsum is minutely roughened and subopaque basad, and its erect hairs are sparse and often coarse; gastric pubescence sparse, appressed and inconspicuous. The pronotal disc has a single anterior pair of long, posteriorly inclined standing hairs, but one or both hairs are missing in some specimens, and may have been rubbed off.

A. simo ni combines features of inermis and diegensis , but has 3 or more coarse, irregular teeth along the inner border of each mandible in addition to the preapical tooth or angle (fig. 5). These teeth are broad-based and involve the whole medial border, not just the ventral medial margin, and they are larger, sharper, and more regular than in any other form in the inermis group. Color, size and pilosity-pubescence are as in inermis . Sculpture is intermediate between that of inermis and diegensis : head very finely longitudinally striolate, dull-sericeous nearly back to nuchai carina; pronotum opaque to feebly shining, finely and densely punctate-striate or rugulosestriate, arched anteriorly and becoming longitudinal or oval-concentric behind, interspersed are numerous fairly coarse punctures and sometimes the sculpture is a bit weaker and feebly shining in the middle of the disc. Mesopleura either smooth and shining or dull in the middle; propodeum finely and densely punctate, with superimposed transverse costulation crossing the dorsum. Gastric dorsum usually smooth and shining (rarely roughened and dull).

Propodeal teeth small, but acute; upper corners of, petiolar node produced as definitely acute teeth, though these are usually rather short. Compound eyes 0.17-0.20 mm greatest diameter.

Samples fitting this description are found along the rim of northern South America, mostly in or near mountainous regions, from Venezuela to Ecuador. In the last country, the available records are all from the Pacific side of the Andes. The type locality is Caracas, Venezuela. Other records from: Venezuela: Aragua State, Rancho Grande, 110 m, wet forest litter (W. L. & D. E. Brown). Rancho Grande to Ocumare, 700 m, wet forest litter (Browns). Colombia: Valle Dept., Municipio Buenaventura, Plantation of Palmeras del Pacifico, wet lowland forest litter (W. L. Brown). Ecuador: Pichincha Prov.: 4 km E Santo Domingo, rain forest litter (S. & J. Peck, B-304); 3 km E of Tandapi, 1300 m, wet ravine (Pecks, 1975). Manabi Prov.: 75 km NE of Chone, 300 m (Pecks, B-346). Guayas Prov.: 3 km S of Bucay, lowland rain forest in rotten stick in litter (Brown, E-21).

Two samples from Colombia: 7 km N of Leticia, forest litter, (S. & J. Peck, B-230), 2 workers; and Ecuador, Pastaza Prov.: 22 km SW of Puyo, forest litter (Pecks, B-362), one worker, are deep brownish-orange in color and have the sculpture and pilosity of inermis , but the propodeal and petiolar teeth are well-developed and acute.

In the specimen from SW of Puyo, the punctulae of the anterior pronotum tend to form arched striation, and the inner mandibular borders are irregularly, coarsely, serially toothed (much as in fig. 5), the teeth involving the dorsal inner margin, which is not distinguishable from the ventral inner margin in this case. This specimen probably should be assigned to simoni ; its eyes are about 0.17 mm in greatest diameter.

The two workers from near Leticia, on the other hand, are essentially like inermis in all traits except the acute propodeal and petiolar teeth, and in slightly smaller eye diameter (0.17-0.18 mm). In any case, these two cisandean samples make plausible intergrades between inermis and simoni , and lead to the hypothesis that simoni is just a peripheral forest ecotype of the essentially savanna species inermis . Another hypothesis is that inermis and simoni are hybridizing at points of parapatry. More samples from the western edge of the Hylea and from the Hylea-savannah boundary would probably be helpful in deciding among various possible relationships.

A. diegensis (fig. 44) has been collected at or near the type locality, Rio Don Diego (and Quebrada Guacoche), Guajira Dept., Colombia, in lowland rain forest leaf litter at the seaward base of the Sierra Nevada de Santa Marta (W. L. Brown & C. Kugler), and also near Santa Marta, Magdalena Dept., at the hamlet of Digrera in a shady creek bed at the base of the same sierra (Brown & Kugler). These «typical» members of the species have the sculpture more «normal» for Anochetus than does A. inermis ; that is, the sculpture is more rugged and rugose where it occurs, and smooth or nearly smooth, shining areas are more extensive. Pronotum smooth and shining to indistinctly striate and subopaque discad, but even in the smoothest specimens, some fine rugosity or striation usually exists along the front and sides of the pronotum. Mesopleura usually smooth and shining, except for striate or rugulose ends of the sclerite. Vertex finely longitudinally striate in the middle for varying distances, but the posterior fifth, more or less, is smooth, or nearly smooth, and shining, including much of «occipital» lobes. Propodeum punctulate-rugulose or punctulate-costulate, the individual rugules or costules usually distinct, at least on the upper sides and transversely across the dorsum. Petiolar node often finely reticulate-rugulose basad, shining above; gaster smooth and shining, but with numerous fine punctures from which arise the fine appressed and decumbent hairs of the abundant and conspicuous pubescence. Standing longer pilosity more abundant than in inermis , and usually finer; at least 6, and usually more than 10, standing hairs on pronotal disc, but usually none on mesonotum or propodeum (rarely 1 on propodeum).

Propodeal angles each with a small, acute tooth; free angles of petiolar node produced as acute teeth, varying in length and angle of divergence (fig. 44). Mandibles with edentate inner dorsal margins basad of preapical angle, but ventral margins often have low teeth or denticles, and the most distal of these may protrude beyond the dorsal margins even in perfect full-face view of head (as in figs. 6, 7 or 8). Compound eyes of worker 0.15-0.20 mm greatest diameter.

The northern Colombian samples tend to be dark in color, with deep reddish-brown trunk and gaster, and head and petiole usually somewhat lighter and more reddish. Samples from Panama (Barro Colorado Island, Zetek, Brown and other collectors; Quipo, J. Zetek) are much lighter in color, light yellowish-brown with yellow legs, but otherwise resemble diegensis ; thus the species bierigi was synonymized by Brown (1964: 215) with the former species. Samples of the same color as the Panamanian ones occur, interestingly, in Trinidad at the localities listed below, where they must be nearly sympatric with inermis in the Northern Range, yet no intergradient specimens are known among the extensive collections from this island. Trinidad: Morne Bleu, Northern Range (N. A. Weber, No. 209.2). Northern Range, Tucuragua R., 100 m (Weber, No. 155). Northern Range (Weber, No. 252.2). Mile 10 to 12, Arima-Blanchisseuse Road (Weber, No. 207.5). Caparo (P. B. Whelpley).

Specimens from other scattered localities in northern South America are further light-colored examples of typical diegensis : Venezuela, Carabobo State: San Esteban, disturbed lowland forest (W. L. and D. E. Brown). Ecuador, Napo Prov.: 20 km S of Tena, forest litter (S. and J. Peck). Surinam: Dirkshoop and La Poulie, soil and litter samples (I. van der Drift).

Another form, very similar to the yellowish-brown variant of diegensis , is represented by a few samples (6 workers) from the eastern Hylea. This form differs from diegensis in having smaller eyes (greatest diameter 0.12-0.13 mm) and the inner mandibular borders each effectively single, with 2-4 broad, vague preapical teeth forming a variable, crooked margin (fig. 7). Brazil, Pará State, near Belém: Utinga Tract, 3 stray workers from forest litter berlesates (W. L. Brown and P. F. Darlington). Icoaraci, forest litter berlesate, 1 worker (Brown). Guyana: Dunoon 2 workers (F. M. Gaige).

Still another entity, corresponding to the type of A. targionii , comes from widely separated parts of the Amazon drainage; the lone type is labeled simply «Bolivia». Other localities: Brazil, Amazonas State: Reserva Ducke, Mun. Manaus, rain forest, 1 worker from rotten log (W. L. and D. E. Brown). Pará State: Belém vicinity, 1 worker (K. Lenko). Icoaraci, near Belém, 1 worker (W. L. Brown). Pirelli Rubber Plantation, Iriboca, near Belém, 1 worker (P. F. Darlington); the Pará samples are all strays from leaf litter during August 1962. Mâto Qrosso State: Sinop, in N part of the state, several dealate queens (M. Alvarenga). Bolivia, Beni Prov.: Tumupasa, 1 dealate queen (W. M. Mann). Huachi, 1 worker (Mann). Ecuador, Napo Prov.: Limoncocha, 2 workers from forest litter berlesate (S. and J. Peck).

A. targionii is essentially like diegensis , and has two corresponding color forms; the eyes are similar in size (greatest diameter 0.14- 0.17 mm). The mandibles (fig. 8) are edentate along both upper and lower margins of the inner borders, and even the preapical angle is usually reduced to a rounded corner, and the preapical excision is therefore sometimes, poorly marked. The mandible is thus less strongly broadened apicad than in related species; this is especially true of the type and the other Bolivian samples. A notable trait correlated with the edentate mandibles, at least in the meager material available, is the extreme hairiness of the body. There are more standing hairs on the pronotum than can easily be counted, and numerous posteriorly-inclined fine hairs grace the mesonotum and propodeal dorsum, as well as the gastric dorsum. The appressed-to- decumbent pubescence is also well-developed on the head, and fairly well on the gaster, except in 2 exceptionally hairy individuals (yellowish in body color) with rugulose-punctulate pronotum; the sculpture concentric around a small median strip that is smooth or nearly so, and shining. In these hairy specimens, not only are the longer standing hairs more numerous, but the pubescence apparently is increased and slightly lengthened and assumes an obliquely erect posture, even on the head and anterior surface of the petiolar node; the type itself appears to belong to this phenon, although it is somewhat rubbed (Tumupasa, Bolivia, and Belém, Pará).

Thus it is not impossible that even nominal targionii itself consists of two closely related Amazonian forms, but the available material is much too scanty to decide this question, and I am including all the samples with edentate inner mandibular borders and pilose mesonotum and propodeum provisionally in targionii .

The diegensis-like form from Pará and Guyana, previously discussed above, is sympatric with targionii , at least in the vicinity of Belém. It could represent a form of diegensis suffering character displacement in the presence of targionii , or it could be a completely separate species. We need more material, including nest series, to help decide these questions. Unfortunately, Anochetus of the inermis group do not seem to be very common in the Amazonian forests, so it may take a long time to gather the evidence.

The entire set of problems involving inermis and its relatives is complex and tantalizing. We are dealing with possibly as many as 6 different species, yet almost every conceivable combination and degree of intermediacy among them occurs somewhere in South America. It is not even beyond all possibility that all of the forms belong to one extremely plastic species that readily engenders ecotypes (or ecophenotypes) to fit different environments, as many plants and animals are known to do. That at least some real species gaps exist in this complex, however, is indicated by two circumstances.

The first of these circumstances is the known sympatry, or parapatry, apparently without hybridization, of several forms, particularly of «typical» inermis and diegensis in Trinidad and northern Colombia.

The second circumstance is the presence in collections of a number of males, mostly taken at light or in Malaise traps, that are about the right size to belong to the inermis group; at least some of them - perhaps as many as 4 or 5 different species - may correspond to the workers and queens, known or unknown, of this group. These males differ markedly among themselves in genitalic structure; only one of them ( inermis ) is reasonably securely associated with the worker-queen castes (figs. 66, 67). Several of these males are known from a restricted area of Pichincha Province in western Ecuador; terminalia of one of these are shown in figures 72 and 73. The characters of the terminalia suggest that capture of colonies with males, or the rearing of males in artificial nests, will likely lead to a clearer understanding of species limits and variation in worker-queen characters in these and other species-groups of Anochetus .

The species of this group live in the litter and upper soil layers, where they hunt small soft-bodied arthropods. In the llanos of central Venezuela, I found inermis in grass roots and litter in the shade of trees and shrubs; in wet forest, the nests of simoni are often found in rotten twigs in the litter. Nests seem usually to contain 30-50 workers. Although normal dealate queens occur in some nests, ergatoid queens also may serve as apparent reproductives. The ergatoid queen is like the worker, with slightly larger compound eyes and a single median ocellus, and the tr,unk is more convex in side-view outline, especially the propodeum.

When disturbed, O. inermis can press its body against the substrate and remain motionless for long periods, but it is also a fast and agile runner when danger presses.