Pachycondyla striata

Pachycondyla striata nests in rotten wood, under logs, or in the soil and forages on the soil surface (Mackay and Mackay).

Identification
From Mackay and Mackay (2010): There are several species of New World Pachycondyla in which the workers and females have conspicuous striae on the dorsum of the head, including Paltothyreus tarsatus, Pachycondyla fuscoatra, Neoponera lineaticeps, Neoponera magnifica and P. striata. Pachycondyla striata can be easily separated from P. tarsata, as it lacks the inner claw on the tarsal claws and the swellings on the upper anterior region of the postpetiole, both of which are present in P. tarsata. Pachycondyla striata differs from N. lineaticeps in the shape of the petiole, which is nearly rectangular, not with the posterior face broadly rounded into the dorsal face. Additionally P. striata is much larger (total length of N. lineaticeps 10 mm). Pachycondyla striata can also be separated as it occurs mostly in southern South America, not Central America and northern South America as does N. lineaticeps. The striae on the head and dorsum of the pronotum of P. striata are not as coarse and well defined as they are in N. magnifica. Pachycondyla striata has approximately 50 striae across the widest point of the pronotum, whereas N. magnifica has about 35. Pachycondyla striata could be easily confused with P. fuscoatra. It differs in having a well-developed pronotal carina (lacking in P. fuscoatra) and the stria on the head are finer and not as well defined. Pachycondyla striata can be confused with Pachycondyla impressa, but differs in that P. impressa lacks the striae on the head and lacks a well-developed carina on the pronotal shoulder. Otherwise they are very similar.

The males of three common species are very similar: P. striata, P. impressa and Neoponera villosa. Pachycondyla striata can be separated from the other two by the presence of dense erect hairs on most of the surfaces (sparse or only moderately abundant in the other two species). The subpetiolar process of P. striata is angulate anteriorly, not broadly rounded as in P. impressa, or with a large ventral process in N. villosa.

Distribution
BRASIL, BOLIVIA, PARAGUAY, ARGENTINA, URUGUAY (Mackay and Mackay 2010)

Distribution based on Regional Taxon Lists
Neotropical Region: Argentina, Brazil, Paraguay, Uruguay.

Habitat
Pachycondyla striata can be found in wet myrtaceous forest, rain forest, riparian rain forest, open grassy areas and cerrado [scrub vegetation], at sea level to 1300 meters elevation. (Mackay and Mackay 2010)

Biology
Nests of P. striata are simple and poorly elaborated, with the chambers and tunnels horizontally distributed close to the surface of the soil (Silva-Melo et al. 2010). Established colonies (N=7) contained 150 - 384 workers.

Rosumek (2017) assessed trophic resource use and period of activity within the ant community in a southern Brazil Atlantic forest. For this species: Odontomachus chelifer and Pachycondyla striata are two widespread species that differ radically in morphology but are similar in many aspects. It is appropriate to discuss both together. They are one of the most conspicuous elements of the southern Atlantic forest ground fauna, due to their abundance, solitary foraging mode and large size. Several accounts show these species occupy a multitude of functional roles and have a broad trophic niche. Observation of nest entrances showed that 80-90% of the items carried by P. striata were arthropod parts, mostly termites and other ants, with the remainder consisting of plant material (Giannotti & Machado, 1991; Medeiros & Oliveira, 2009). Through direct observation, Medeiros and Oliveira (2009) also showed that scavenging accounts for more than 80% of its foraging behavior. On the other hand, Fowler (1980) reported O. chelifer prefers certain termite species in the laboratory, and qualitatively stated that in the field prey consisted almost entirely of termites. In the Atlantic forest, all items carried to nests were arthropods, mainly termites, but other animal groups accounted for 60% of them (Raimundo et al., 2009). Scavenging was also cited in this study, although not quantified. Both O. chelifer and P. striata were recorded on experimental carcasses predating the larvae and pupae of necrophagous insects (Paula et al., 2016).

Other important items used by the two species are seeds with elaiosomes and other fallen diaspores rich in proteins and lipids, frequently collected from the ground in the Atlantic forest (Pizo & Oliveira, 2000; Passos & Oliveira, 2002, 2004). Field records on use of liquid sugars are scant and qualitative. Odontomachus chelifer was not observed using extra-floral nectaries by Raimundo et al. (2009), while there is one record for P. striata (in Cerrado, the Brazilian savannah – Byk & Del-Claro, 2010).

The results presented here are mostly consistent with this broader picture. Both species more frequently foraged upon dead insects, sucrose and large prey. In fact, they were the only two species consistently recorded on crickets. The low frequency in termite baits is unexpected and probably represents a methodological artifact. These large solitary foragers were observed quickly collecting termites (even glued ones) and leaving the baits in a few minutes, contrary to ants of smaller species that recruited to them. In cricket baits, however, the two species spent more time trying to carry out the tied cricket or dismembering it. Smaller ants frequently took advantage of this to grab the remains or lick spilled hemolymph. This largely contributed to the richness found in this bait and could happen in nature, whenever predators kill prey too large to carry them out at once.

Besides predation, scavenging was a common behavior, and P. striata in particular would prioritize it whenever possible, in accordance with what was observed by Medeiros and Oliveira (2009). This could be result of their morphology, because the triangular mandibles may be more suited to chop large carcasses than the trap-jaws of O. chelifer. In addition, it could be an effect of competition. The two species were never found at the same bait, and co-occurred in just 10 of the 62 points where they were recorded. The two were previously reported to avoid each other, but, when agonistic interactions occur, P. striata usually is the winner, and can steal the food or kill (and eat) O. chelifer (Medeiros & Oliveira, 2009; Raimundo et al., 2009). Thus, P. striata could displace O. chelifer and maintain control of a valuable resource such as dead arthropods through tandem recruitment (Medeiros & Oliveira, 2009; Silva-Melo & Giannotti, 2012), while cooperative foraging behavior was not observed in O. chelifer (Raimundo et al., 2009). Effectively, the average numbers of workers per bait was smaller for the latter species (O. chelifer = 1.4 ± 0.9; P. striata = 2.5 ± 2; Mann-Whitney, z = -2.27, p = 0.02).

Both species used sucrose frequently and rarely foraged on melezitose (anolog for honeydew). They were never observed foraging on trees or low vegetation in this study, which fits previous accounts (Fowler, 1980; Medeiros & Oliveira 2009), so it is unlikely that they commonly use nectar as food source. This behavior also should limit honeydew use by them.

Past results have shown that these species show a preference for day (P. striata) or night foraging (O. chelifer). No preference in their time of foraging was found in this study.

Nomenclature

 *  striata. Pachycondyla striata Smith, F. 1858b: 106 (w.) BRAZIL. Roger, 1861a: 6 (q.); Santschi, 1921g: 86 (m.); Wheeler, G.C. & Wheeler, J. 1952c: 616 (l.). Senior synonym of nitidiventris: Kempf, 1961c: 210. See also: Mackay & Mackay, 2010: 527.
 * nitidiventris. Pachycondyla striata var. nitidiventris Santschi, 1921g: 87 (w.) URUGUAY. Junior synonym of striata: Kempf, 1961c: 201.

Pachycondyla striata

Five worker syntypes in and one worker syntype in. Labelled “Rio. 57/63.” Acc. Reg.: “1857 no. 63 (June 22). Province of Rio. Presented by Rev. Hamlet Clark.”

Three more workers in are mounted in the same way as the syntypes but have passed through the Farren White collection and had their data labels altered to read “Rio. H. Clark.” These are probably also syntypes.

Worker
From Mackay and Mackay (2010): The worker is a relatively large (total length about 13 mm) dark brown specimen with lighter brown appendages. The mandibles have about 12 teeth. The anterior medial border of the clypeus is slightly concave, the eyes are moderately large (0.58 mm maximum diameter) located approximately one diameter from the anterior edge of the head (side view). The malar carina is absent. The scape extends past the posterior lateral corner of the head. The posterior margin of the head is concave. The pronotal carina is well developed and sharp and slightly overhangs the side of the pronotum (similar to that of Neoponera villosa). The metanotal suture is not marked on the dorsum of the mesosoma. The dorsal face of the propodeum slopes broadly into the posterior face, the propodeal spiracle is slit-shaped. The petiole is thick when viewed in profile and rectangular-shaped. The anterior face of the postpetiole is vertical and sharply bends into the dorsal face, nearly forming an angle. The dorsal face of the pygidium is concave, as in Pachycondyla impressa.

Erect hairs are present on most surfaces, including the clypeus, dorsal and ventral surfaces of the head, sides of the head, scapes, dorsum of the mesosoma, legs, including the tibiae, dorsal surface of the petiole and all surfaces of the gaster; appressed golden pubescence is sparse on most surfaces except the gaster, where it is moderately dense.

The dorsum of the head is mostly finely striate longitudinally; the striae are poorly developed on the sides of the head, but striae are present on the side of the mesosoma as well as the dorsum. The side of the petiole is nearly without striae; the dorsum of the petiole has mostly transverse very fine striae. The gaster is mostly punctate.

Queen
From Mackay and Mackay (2010): The female is similar to the worker in lacking the malar carina, having relatively large eyes, a well-developed carina on the pronotal shoulder and a similar shaped petiole. It is a large (total length 15 mm) black specimen with brown legs.

Erect and suberect golden hairs are abundant on the mandibles, clypeus, dorsal and ventral surfaces of the head, posterior margin, sides of the head, dorsum of the mesosoma, dorsum of the petiole, subpetiolar process and all surfaces of the gaster. The hairs on the legs are similar and abundant but are mostly suberect. Appressed golden pubescence is dense on most surfaces, but is fine and hides little of the surface sculpturing.

The striae are also present on the dorsum of the head but are poorly developed, especially on the sides of the head. The mandibles are mostly covered with fine striae. The dorsum of the pronotum has numerous mostly longitudinal striae, the scutum and scutellum are covered with coarse longitudinal striae. The mesopleuron and metapleuron are covered with fine nearly horizontal striae; the remainder of the ant is dull and punctate.

Male
From Mackay and Mackay (2010): The male is a large (total length 13 mm) dark brown specimen. The anterior edge of the clypeus is convex to slightly concave and the clypeus is swollen in the middle. The eyes are large and occupy approximately one half of the side of the head. The ocelli are small (maximum diameter of the median ocellus 0.12 mm), the median ocellus is located 0.2 mm from the lateral ocellus, which is greater than the diameter as the median ocellus.

The pronotal shoulder is swollen and forms a raised area, which is broadly rounded. The propodeal spiracle is slit-shaped. The petiole is thick when viewed in profile with the two faces converging dorsally and forming a rounded apex. The subpetiolar process is angulate anteriorly and gradually diminishes posteriorly. Coarse erect hairs are extremely abundant on all surfaces, especially the head, the mesosoma and petiole. Fine appressed golden pubescence is also abundant on most surfaces.

The head of the male is punctate or coriaceous, as is the mesosoma and the petiole, the gaster is finely punctate, most surfaces are dull, the mesosoma is weakly shining, as is the petiole, the gaster slightly more shining.

Type Material
Brasil, Rio de Janeiro; Uruguay, Nueva Helvetia; Brasil, Mato Grosso, frontier with Bolivia. 2 syntype workers seen, ; 4 cotypes seen,. (Mackay and Mackay 2010)

Etymology
The name of this species is derived from the Latin word stria, meaning channel or furrow, referring to the striae on numerous parts of the body, especially the pronotum. (Mackay and Mackay 2010)