Probolomyrmex boliviensis

This is the only species of the genus for which there is any substantial biological information. Taylor (1965) collected a colony, or possibly a colony fragment, in Panama that he was able to keep in a laboratory observation nest.

Identification
Oliveira & Feitosa (2019) - Antennal scape extends to posterior third of cephalic capsule, distance from scape apex to posterior margin of head less than or equal to two times pedicel length. Postero-ventral lobe of petiole short and rounded. Subpetiolar process weakly developed. Prora and dorsal protuberance on posterior region of first gastral tergite present.

P. boliviensis is similar to Probolomyrmex guanacastensis, but the latter is smaller and has distinctly shorter scapes. Both species are found in Costa Rica but differ in habitat. Probolomyrmex guanacastensis is restricted to the Guanacaste region, in tropical dry forest with average rainfall below 1700 mm/year. Costa Rican P. boliviensis are known from Limón and southern Puntarenas provinces, in tropical submontane rainforests up to 1000m and average rainfall between 3500–5000 mm/year (Janzen, 1991; IMN, 2019).

Distribution
Occurs in rainforests of northern South America, from Panama to Bolivia.

Distribution based on Regional Taxon Lists
Neotropical Region: Bolivia, Colombia, Costa Rica, Honduras, Panama, Peru.

Biology
The holotype, a queen, was found found beneath a stone near a small colony of Ponera. Cover and Tobin made a colony collection from a rotten chunk of wood half buried in the soil.

Taylor (1965) - The following notes are based on a series of ten workers and five queens from a colony collected by the author on June 21st, 1961, at the type locality, Barro Colorado Island.

My Barro Colorado accession originally consisted of 22 workers, 7 queens (4 alate), 11 pupae (9 worker, 2 male), 2 pharate pupae and 6 larvae of various instars. These were collected from an old beetle gallery in a fairly sound, dry portion of a rotting branch about 30 cm. long and 8-10 cm. in diameter, lying on the floor of primary rainforest. The ants were in a single group occupying almost 3 cm. of the gallery, which was about 6-10 mm. in diameter. An aspirator device was used for collection, and it is presumed that the whole colony, excluding foragers, was taken. One of the queens was more worn than the others and appeared to be the “motherqueen” of the colony. The specimens were immediately placed in a glass-topped plaster-of-Paris observation cell, in which they survived for six days until the death of the queen and the larvae disrupted their behaviour. A number of eggs were accumulated during this period, at least two of them being laid by the queen. One worker completed its development while under observation.

Various small soil arthropods including assorted Collembola, Symphyla, small immature spiders, larval and adult ants, Diptera, Coleoptera and termites at all stages of development, and various arthropod and other eggs collected from leafmould, were placed in the nest from time to time. None of these organisms were attacked or accepted as food; indeed, the ants usually retreated hurriedly with their brood when confronted by other animals.

The larvae and pharate pupae, still enclosed in larval cuticles, were not placed by the nurse workers on the nest floor, but were attached to the plaster walls or glass ceiling of the brood chamber by the peculiar terminal abdominal suspensory tubercles described above (p. 348), so as to hang head downwards. Eggs and pupae were normally placed on the floor of the brood chamber, but under moist conditions they too were attached to the nest ceiling, presumably being held there by the surface tension forces of the moisture film on the glass. Pupae were invariably placed with the frontal region of the head adherent to the ceiling, and the eggs were attached either directly to the ceiling, or to the bodies of larvae or pupae.

The workers were very active and “excitable”, being reminiscent of Leptogenys or Platythyrea in this regard. They ran quite rapidly and "nervously" when disturbed and, even when settled, were constantly active, grooming themselves and their partners. The larvae were assiduously attended and were almost constantly being licked by one or more of the workers. The suspended brood was usually placed immediately above the main adult cluster, the nurse workers moving on to the ceiling to attend to the larvae.

Workers were not observed transporting their fellows, but the queen was carried about 5 cm. in the jaws of a worker on one occasion. She lay in a pupal posture and was held by the frontal part of the head, lying ventral side uppermost along the underside of the transporting worker. Pupae were always normally carried in this way, although they were sometimes dragged by the legs or antennae when being positioned by nurse workers. The larvae were always carried along the underside of transporting workers and were invariably gripped about the neck of the terminal abdominal suspensory tubercle. This mode of grasping the larvae appeared to facilitate their placement on the nest ceiling by the workers. The newly emerged workers are highly callow, and apparently take about 5 days to attain full coloration.

Nomenclature

 *  boliviensis. Probolomyrmex boliviensis Mann, 1923: 16, fig. 2 (q.) BOLIVIA. Senior synonym of angusticeps: Brown, 1975: 11. See also: Taylor, 1965d: 361.
 * angusticeps. Probolomyrmex angusticeps Smith, M.R. 1949b: 39 (w.) PANAMA. Taylor, 1965d: 360 (q.l.). Junior synonym of boliviensis: Brown, 1975: 11; Agosti, 1995: 432.

Worker
Oliveira & Feitosa (2019) - (n=35) HL 0.63–0.72; HW 0.37–0.42; SL 0.43–0.56; WL 0.85–1.02; PL 0.31–0.41; PW 0.31–0.36; PH 0.27–0.36; TL 2.78–3.27; CI 56.5–61.5; SI 67.5–77.5; PI 76.5–94.5.

Fronto clypeal shelflike projection with hair-bearing tubercles or cylindrical micro-pegs. Mandibles densely punctate; external surface of mandibular basal margin smooth. Antennal funiculi with pits in each segment, tip of apical segment bearing pits of different sizes. Mesopleuron, metapleuron and lateral faces of propodeum alveolate; alveoli denser just above metapleural gland orifice; opening of metapleural gland narrow, with smooth anterior region surrounded by rows of hairs. Petiolar node with incomplete foveae, intercalated by micropunctures; latero-ventral region of petiole imbricate; subpetiolar process alveolate. Posterior region of second gastral tergite with transversal rows of deep rounded pits. Space between mesosomal foveae covered by dense pubescence. Pygidium with dense pubescence and few long and thick hairs. Head 1.7 times longer than wide.. Hypostomal margin flattened. Antennal scapes extend beyond head midlength, distance from scape apex to of head less than or equal to two times pedicel length (SI 67.5–77.5). Propodeal declivity emarginated laterally by narrow and dark carina, with teeth at their apexes. Petiole in lateral view at least 1.2 times longer than high (PI 76.5–94.5), posterodorsally with two weakly developed, round, projections; node posterior face short, concave, and smooth; postero-ventral lobe short and rounded; subpetiolar process weakly developed, many times forming acute anterior projection. First gastral segment with prora and dorsal protuberance on posterior region of tergite, characterized by a gentle elevation of the integument.

Queen
dealated. Length 2.8 mm. Head about one and one-half times as long as broad, with slightly convex sides, rounded occipital angles and straight border; vertex and posterior portion of head broadly and evenly rounded, anterior part projected as a thick plate, broader than long and truncated in front, completely covering the mandibles. Clypeus on the anterior truncated portion, triangular, not sharply defined. Mandibles small and rather slender, blades rounding into the basal portions, with two indistinct and blunt teeth. Maxillary palpi 3-jointed, the first and second joints subequal in length and together as long as the third. Labial palp small, apparently 2-jointed. Frontal area rather large, feebly impressed. Frontal lamellae fused into a high, thin plate, strongly convex in profile; behind separated and very short. Antennal insertions near front margin of head, bordered by a fine carina. Antennm 12-jointed, scape extending about four fifths the distance to occipital corners; funiculus evenly enlarged distally, without club; first funicular joint longer than broad; joints 2-10 transverse; terminal as long as the three preceding joints together. Eyes small, little convex, situated at middle of sides. Ocelli small. Thorax long and rather narrow, moderately convex above and at sides, humeri broadly rounded Mesonotum one and one-third times as long as broad. Scutellum longer than broad, rounded behind, with feeble impressions at middle of sides. Epinotum with feebly convex base and nearly flat declivity, bluntly dentate at angle. Petiole elongate nodiform; from above, twice as long as broad, with the posterior margin concave at middle and subdentiform at sides; in profile longer than broad and nearly twice as thick behind as in front, its ventral outline bisinuate, with a blunt antero-ventral tooth; posterior surface strongly concave. Gaster slender, strongly constricted between the first and second segments, first segment narrowed in front, shorter than the second, remaining segments small, directed downward. Sting well developed and strong. Legs long, rather slender, tibial spines coarse, those on posterior pair strongly pectinate.

Opaque, finely, densely reticulate and in addition with rather coarse, foveolate punctures, especially prominent on the front of head, epinotum and gaster. Pubescence white, very fine, closely appressed, moderately abundant, more so on gaster and appendages.

Brownish red, appendages brownish yellow.

Oliveira & Feitosa (2019) - (n=3) HL 0.63–0.70; HW 0.40–0.50; SL 0.44–0.61; WL 0.89–0.93; PL 0.32–0.33; PH 0.29–0.31; TL 2.96–3.08; CI 61.5–69; SI 76.5–77.5; PI 86.5–94.5.

With the morphological modifications described for Probolomyrmex queens and the diagnostic characters of the workers.