Protanilla lini

 Protanilla lini is distributed across the north and central parts of Taiwan, primarily in natural or seminatural areas above an altitude of 600 m. Protanilla lini workers seem to be spotted more easily on rainy days, possibly because of migrations caused by floods. (Hsu et al. 2017)

Identification
Terayama (2009) - Easily separated from the Chinese species; from Protanilla bicolor by the round petiole and postpetiole in dorsal view (petiole and postpetiole oval, and longer than wide, respectively, in bicolor), and the concolorous body (bicolored in bicolor), from Protanilla concolor by the reverse U-shaped petiolar node in profile (subtriangular in concolor), and round postpetiollar node in dorsal view (postpetiole short, wider than long in concolor), and from Protanilla furcomandibula by the thinner mandible (broader in furcomandibula), and the absence of lateroventral tooth of mandible (two lateroventral teeth present in furcomandibula).

Hsu et al. (2017) - Worker: a longitudinal inconspicuous groove running along dorsolateral margin of mandible, traversing the width to inner margin at approximately half the length. A series of long stout hairs on masticatory ventral apex of mandible. Presclerites of abdominal segment IV constricted to articulation with postpetiole; pretergite thin; presternite bulging and coarsely sculptured.

Distribution based on Regional Taxon Lists
Oriental Region: Taiwan. Palaearctic Region: Japan.

Biology
Hsu et al. (2017) – A colony was collected from the Lienhuachih Forest Dynamics Plot at an altitude of 760 m. The area is a Machilus-Castanopsis forest zone that is mainly composed of Lauraceae and Fagaceae trees. The colony was found nesting in some cavities and tunnels within a fallen dead branch.

The P. lini colony was observed in our laboratory for 2 months (a colony of Protanilla jongi was also collected and observed). All of the members demonstrated the behavior noted by Wilson and Hölldobler (1990), which is consistent with those of typical trap-jaw ants (e.g. Odontomachus and Anochetus). Although mandibles of Protanilla workers are not linear in shape, they are able to open to 180 degrees and strike during predatory interactions. This behavior was also recorded in P. wallacei a few times in the laboratory (F. Ito, personal communication). Furthermore, we observed that Protanilla workers locked their mandibles in the striking position when guarding their nest entrances in the laboratory. The guarding behavior was also recorded in Leptanilla japonica by Masuko (1990), who noted that most of the workers stood near the brood pile facing outward, with the anterior half of the body raised, the forelegs suspended in the air, and the mandibles open. However, whether Leptanilla could quickly snap their mandibles as those of Protanilla and other trap-jaw ants was not mentioned in the previous articles.

In our laboratory observations, we provided various types of prey (centipedes, cockroaches, meal worms, termites, springtails, and woodlice). Only certain types of centipedes were accepted; specifically, they appeared to prefer geophilomorph centipedes that were approximately 3–4 cm in length. Smaller and larger geophilomorph centipedes were also acceptable, but the members were unable to finish those exceeding 4 cm. We removed them to avoid a sanitation problem in the nest. This observation is similar to the ecological notes in Ogata et al. (1995), which reported that Leptanilla taiwanensis larvae were found in the field feeding on a geophilomorph centipede approximately 4 cm in length; Masuko (1990) also demonstrated this phenomenon, indicating that L. japonica exclusively fed on geophilomorph centipedes ranging from 1–2 cm in the laboratory (but whether centipedes larger than 2 cm were provided is unclear). However, "P. wallacei" was observed to feed on Occasjapyx diplurans (Billen et al. 2013). Further field and laboratory observations are required to determine the degree to which Protanilla and other Leptanillinae specialize on centipedes.

In our captive colonies, when a live centipede was encountered, the workers grabbed the appendages of the centipede by quickly snapping their mandibles and stinging the victim. The centipede was paralyzed within a few minutes and transported back to the nest, where it was consumed by numerous larvae that were carried and attached to the prey by the workers. We did not observe the situation discussed in Masuko (1990), where L. japonica workers carried the larvae toward the paralyzed prey rather than bringing the prey back to the nest.

However, whether the synchronized larval development and larval hemolymph feeding behaviors in L. japonica also appear in Protanilla species remains unclear. In our observations, we did not record the gynes of either species feeding on larvae. Nevertheless, during the 6-month observation of the P. lini colony, we did note the larvae of different instars present in the colony at the same time. More living material of Protanilla species is needed for the further examination of larval biology.

In addition, strong and distinct odors spread when the colony was excavated and even when undisturbed in the laboratory. However, it remains unclear whether the odor was produced by adults or larvae.

Nomenclature

 *  lini. Protanilla lini Terayama, 2009: 126, figs. 113-118 (w.) TAIWAN.

Worker
Holotype. Head long, smooth and shining, 1.26 times as long as wide, with almost straight posterior margin and convex sides in full face view. Mandible elongate-triangular, with about 10 peg-like denticles in ventral portion. In profile apical 1/3 of mandible curved ventrally. Anterior margin of clypeus concave at middle. Antenna with 12 segments; scape long, microreticulate, exceeding posterior margin of head, SI = 74; 2nd segment (pedicel) longer than wide, 3rd to 11th segments each almost as long as wide; terminal segment 2.3 times as long as wide. Eye lacking.

Alitrunk long and slender; pronotum smooth and shining; mesonotum thin, 0..5 times of width of pronotum in dorsal view; propodeum smooth and shining, with convex dorsal margin and convex posterodorsal corner in profile. Petiolar node higher than long, smooth and shining, with convex dorsal margin and almost straight anterior and posterior margins; in dorsal view, dorsal disc round, as long as wide; subpetiolar process low, bearing lobe-like. Postpetiole higher than long, and lower than petiole, with well convex dorsal and ventral margins; in dorsal view, dorsal disc round, as long as wide. Gaster largely smooth; in dorsal view, 1st gastral tergum with straight anterior margin and dully angulate anterolateral corners, 0.50 mm in maximum width.

HL 0.60, HW 0.48, SL 0.50, WL 0.93, PL 0.23, PH 0.33, DPW 0.23, PPL 0.23, PPH 0.33, PPW 0.24, TL 2.9.

Color. Body yellowish brown; antenna and legs somewhat yellowish.

Queen
Hsu et al. (2017) - HL 0.63, HW 0.54, CI 86, SL 0.52, SI 96, ML 0.31, PW 0.42, WL 1.03, PNL 0.24, PNH 0.41, PNW 0.28, PPNL 0.22, PPNH 0.43, PPNW 0.32.

Body yellowish-brown, similar to worker. In full-face view, head somewhat round, as broad as long; sides convex; posterior margin straight to slightly concave. Compound eyes large, located slightly above the middle of sides of head. Ocelli present. Clypeus same shape as in workers. Mandibles long and triangular, with a longitudinal groove running dorsolaterally, traversing the width to inner margin at 1/3 the length to apex; masticatory margin slightly crenulate with approximately 15 peg-like teeth; apical 1/3 denticulate and without peg-like teeth. A series of long stout hairs on masticatory ventral margin of mandibular apex, with the foremost one stoutest. In lateral view, mandibles down-curved apically. Antennae 12-segmented; scape long, reaching posterior margin of head; segments 2–11 as long as wide; terminal segment approximately 1.5 times as long as wide. Mesosoma well developed, in lateral view with a flat to slightly convex dorsal outline. Pronotum in dorsal view approximately as long as scutum, with convex sides, in lateral view with a convex dorsal outline. Scutum in dorsal view triangular, in lateral view with a flat dorsal outline. Scutellum in dorsal view small, half the length of scutum, in lateral view with a flat dorsal outline. Propodeum in dorsal view trapezoidal, with straight posterior face and round corners, in lateral view with round dorsal outline. Propodeal spiracle large, above bulla of metapleural gland. Petiole and postpetiole same shape as that of workers in both dorsal and profile view, but in lateral view petiole and postpetiole thinner than those of workers.

Type Material
Holotype. Worker, Fusan, Taipei Pref., 18.iii. 1995, C.-C. Lin leg. Paratypes. 2 workers, same data as the holotype. Holotype in NIAES, and paratypes in the collection of the Social Insect Laboratory of NCUE.

Etymology
This species is named after the collector of this species. Dr. C.-C. Lin, who is a leading entomologist.