Paltothyreus tarsatus

The African Stink Ant is a large (17-20 mm) conspicuous predator and scavenger distributed throughout Africa. The populous colonies inhabit ground nests with multiple entrances, revealing an extensive system of shallow tunnels that lead to the foraging grounds (Braun et al. 1994), the entrance often surrounded by excavated soil and remains of arthropods and other food. The characteristic "rotten egg" smell is caused by mandibular gland secretions. These sulphides are released by workers that become buried after tunnels collapse, and this allows nestmates to locate and excavate them (Crewe & Fletcher 1974). Workers usually forage singly. In Benin, Taylor et al. (2018) found it on mango (Mangifera indica) and as prey in nests of Oecophylla longinoda.

Identification
There are currently a number of subspecies recognized (P. tarsatus delagoensis [Emery], P. tarsatus mediana [Santschi], P. tarsatus robusta [Santschi], P. tarsatus striata [Santschi], P. tarsatus striatidens [Santschi] and P. tarsatus subopaca [Santschi]) and possibly some of these may be recognized as valid species when the Old World fauna is evaluated.

From Mackay and Mackay (2010): Paltothyreus tarsatus can be easily separated from all of the New World species by the angulate anterior lateral corners of the postpetiole and the presence of single small teeth on each of the inner margins of the tarsal claws. The specimen from São Paulo is nearly identical to the typical Old World Paltothyreus tarsatus . It can be differentiated by the form of the surface of the medial lobe of the clypeus (which is completely concave with notable longitudinal striae in most Old World P. tarsatus), smooth surface of the mandible (striate and dull in Old World P. tarsatus), the transverse striae on the mesonotum (longitudinal in most Old World P. tarsatus) and by the smooth and glossy dorsal surface of the gaster (smooth and glossy, but with scattered coarse punctures in most Old World specimens of P. tarsatus). It is probable that this specimen of P. tarsatus is a mislabeled Old World species, but it may also represent a new species.

It is interesting to note that the striae on the dorsum of the pronotum are very similar to those of Pachycondyla magnifica (=Neoponera magnifica). The two species are apparently not closely related and easily separated by the claw on the inner border of the tarsal claw and the angles on the postpetiole of P tarsatus, both of which are absent in P. magnifica.

Distribution
From Mackay and Mackay (2010): Smith (1858:94) lists P. tarsatus as being a South American species (Demerara, Pará, Brasil). Unfortunately Neoponera commutata was misidentified as P. tarsatus prior to 1860 (Roger, 1860), which explains Smith’s report.

Distribution based on Regional Taxon Lists
Afrotropical Region: Benin, Cameroun, Equatorial Guinea, Guinea, Guinea-Bissau, Ivory Coast, Kenya, Mozambique, Namibia, Senegal, Sierra Leone, South Africa, Uganda, United Republic of Tanzania, Zimbabwe.

Biology
Although workers of P. tarsatus forage individually, they can recruit nestmates with chemical signals (sternal glands in abdomen) when retrieving bigger or more abundant prey items (Hölldobler 1984). Workers can transfer prey to nestmates during the journey back to the nest (López et al., 2000). Records of prey carried by foragers as well as prey remains outside nest entrances show more than 90 % arthropods, especially termites (Macrotermes) and millipedes, but also ants (mainly Camponotus sp.) and beetles. Examination of 40 complete colonies from savanna and forest habitats in Ivory Coast indicated a mean colony size of 1576 ± 1543 workers (n = 42), and three colonies yielded more than 5000 workers (Peeters et al. 2013). There was a huge quantity of brood, exceeding 1000 eggs and several thousands of larvae in some colonies. Five colonies had more than 1000 cocoons. Some of the bigger colonies (>1000 workers) reared hundreds of winged gynes, with a maximum of 823. Only a few other species scattered throughout subfamily Ponerinae have thousands of workers per colony, e.g. Brachyponera lutea, Centromyrmex bequaerti, Megaponera analis, Neoponera luteola.

Nests are decentralized to allow harvesting food throughout a large home range while reducing predation on foragers. The subterranean tunnels lead foragers away from the nest centre; once on the surface, they do not roam more than 3–5 m from an exit. They use canopy orientation during excursions away from the tunnel exits (Hölldobler 1980).

Paltothyreus tarsatus has volatile material in the venom gland, which includes bitter-tasting cyclic dipeptides (Morgan et al., 2003).

Diame et al. (2015) - An ant diversity study in Senegal orchards found Paltothyreus tarsatus occurred in and preferred high canopy coverage, higher tree diversity and more leaf litter.

Mating and colony foundation
In the Ivory Coast, the mating behaviour of P. tarsatus follows the ‘male-aggregation’ syndrome which is uncommon in Ponerinae (Life History). In contrast, Villet et al. (1989) described a ‘female calling’ syndrome for P. tarsatus in South Africa, where gynes emerged from a nest entrance, climbed low vegetation nearby, and adopted a resting posture; after some time males flew in and mated. Female-calling resembles the sexual behaviour of solitary wasps and may be ancestral in ants (Hölldobler & Bartz 1985). Male-aggregations seem possible only in ponerine species with big colonies and numerous sexuals produced concurrently. The intraspecific variation documented in P. tarsatus suggests that a transition from female-calling to male-aggregation is possible upon an increase in the number of sexuals in the population (Peeters et al. 2013). After mating, ant foundresses are alone for several weeks while they raise the first generation of workers. Foundations are especially hazardous in the Ponerinae because queens must hunt outside the nests and produce workers that are similar in size to themselves (no nanitics) (Life History). This is unlike formicoid subfamilies in which claustral foundresses can rely on histolysis of their big flight muscles and other metabolic reserves. In P. tarsatus, non-claustral foundation has been observed in South Africa (Villet et al. 1989) and in the Ivory Coast. Founding queens presumably have low success rates due to predation while foraging as well as parasitism of unguarded brood. Hence, many gynes must be produced annually to compensate for mortality during both dispersal and foundation itself.

Castes
Winged queens and workers exhibit a pronounced dimorphism in body size.

Nomenclature

 *  tarsatus. Formica tarsata Fabricius, 1798: 280 (w.) SENEGAL. Latreille, 1802c: 736 (q.); Mayr, 1866b: 893 (m.). Combination in Paltothyreus: Mayr, 1862: 736; in Pachycondyla: Brown, in Bolton, 1995b: 310; in Paltothyreus: Schmidt & Shattuck, 2014: 127. Senior synonym of gagates, pestilentia, spiniventris: Roger, 1860: 310; Roger, 1863b: 17; of simillima: Emery, 1892d: 557. Current subspecies: nominal plus delagoensis, medianus, robustus, striatidens, striatus, subopacus. See also: Forel, 1891b: 136; Arnold, 1915: 44; Wheeler, W.M. 1922a: 60; Hölldobler, 1980: 86; Mackay & Mackay, 2010: 545.
 * gagates. Ponera gagates Guérin-Méneville, 1844a: 423 (w.) SENEGAL. Junior synonym of tarsatus: Roger, 1860: 310; Roger, 1863b: 17.
 * pestilentia. Ponera pestilentia Smith, F. 1858b: 92 (w.) SIERRA LEONE. Junior synonym of tarsatus: Roger, 1860: 310.
 * simillima. Pachycondyla simillima Smith, F. 1858b: 105, pl. 7, fig. 17 (q.) SOUTH AFRICA. Combination in Paltothyreus: Mayr, 1886c: 358. Junior synonym of tarsatus: Emery, 1892d: 557.
 * spiniventris. Ponera spiniventris Smith, F. 1858b: 92 (m.) SIERRA LEONE. Junior synonym of tarsatus: Roger, 1860: 310; Roger, 1863b: 17.

Worker
From Mackay and Mackay (2010): The worker is a moderately large (total length 13 mm) dark reddish brown ant. The mandibles have approximately 18 teeth. The median portion of the clypeus is formed into a broad lobe, which overhangs the remainder of the clypeus. The surface of the lobe has two longitudinal depressions separating three distinct lobes (there are exceptions to this). The head is nearly square, with the length (including the lobe of the clypeus) being 3.1 mm, the width 3.0 mm. The eyes are relatively small (maximum diameter 0.56 mm) located slightly more than one maximum diameter from the anterior margin of the head. The scape is relatively short (2.66 mm), extending about 1½ funicular segments past the posterior lateral corner of the head. The sides of the head are slightly narrowed anteriorly, angulate posteriorly, with the medial posterior margin concave. The mesonotum and propodeum are barely separated on the dorsum of the mesosoma, but the metanotal suture is well developed on the side. The propodeal spiracle is elongated. The petiole is relatively narrow when viewed in profile with a distinctly concave anterior face and a broadly rounded convex posterior face, the faces of which form a poorly defined dorsal face. The subpetiolar process is well developed and consists of a thickened triangular lobe. The anterior upper corners of the postpetiole (first gastral tergum) are swollen and angulate. The stridulatory file is apparently absent (pretergite can not be well seen in the specimen from São Paulo, but the stridulatory file is absent in Old World specimens of P. tarsatus). The dorsum of the pygidium is slightly concave. The arolia are not developed. The tarsal claws have a distinct tooth along in inner medial margin on both sides.

Erect hairs are abundant on the clypeus, especially along the anterior border, as they are on the dorsum of the head, the antennal scapes, the sides of the head, the posterior margin, the ventral surface of the head, the dorsum of the mesosoma, all surfaces of the petiole and all surfaces of the gaster; the hairs on the legs are mostly erect, or at least suberect. Appressed pubescence is sparse and noticeable only on the head and the gaster.

The mandibles are smooth and glossy with scattered punctures, the lobe of the clypeus has poorly defined longitudinal striae; the dorsum of the head has well-developed longitudinal striae, which diverge posteriorly. The dorsum of the pronotum has very coarse longitudinal striae, which pass transversely across the pronotum anteriorly and form longitudinal striae on the side the pronotum, the dorsum of the mesonotum has coarse transverse striae as does the dorsum of the propodeum, much of the side of the mesopleuron is smooth and glossy, but the upper region has fine striae, the sides of the propodeum have obliquely directed striae, the petiole is mostly smooth and glossy, but poorly defined striae are present on the sides and transverse striae are present across the dorsum of the node, the gaster is moderately smooth and glossy with scattered punctures.

Queen
From Mackay and Mackay (2010): See the discussion of the tarsatus species complex.

Male
From Mackay and Mackay (2010): See the discussion of the tarsatus species complex.

Type Material
Senegal, Latreille; Sierra Leon; South Africa (Mackay and Mackay 2010)

Ponera pestilentia

Holotype worker in. Labelled “Sierra Leone.” Data of original description gives D.F. Morgan as collector.

Ponera spiniventris

Male in, labelled “Afric. spiniventris Smith.” This is probably the holotype, but the data should be, “Sierra Leone, D.F. Morgan.” Smith stated, “in all probablility this is the male of P. pestilentia.”

Etymology
The name of this species is derived from the Greek word tarsos, referring to the sole of the foot, presumably referring to the unusual form of the tarsal claw. (Mackay and Mackay 2010)

References based on Global Ant Biodiversity Informatics

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