Polyrhachis lamellidens

Polyrhachis lamellidens is perhaps the best known and most studied of all members of the subgenus, probably due to its occurrence in a densely populated country with easy access to colonies (see Hung, 1970: 28–29) (Kohout, 2014). Its nesting habits are different from those of other species of the subgenus with their nests usually found in rotten logs (Yano, 1911) and tree stumps (J. Fellowes, pers. comm.), but also in the ground. Their parasitic lifestyle, in relation to Camponotus japonicus Mayr (as C. herculeanus japonicus) was observed under laboratory conditions by Kohriba (1963). (Kohout, 2014)

Identification
A member of the lamellidens group of the subgenus Polyrhachis. Like Polyrhachis craddocki, this is a very morphologically stable species with no significant variation between populations.

Distribution based on Regional Taxon Lists
Oriental Region: Taiwan. Palaearctic Region: China, Democratic Peoples Republic of Korea, Japan, Republic of Korea.

Polyrhachis lamellidens is known from Japan, Korea, Taiwan and China, including Hong Kong (Kohout, 2014).

Biology
Hung (1970) - Nests of lamellidens are usually found in rotten logs (Yano, 1911), but occasionally underground (Brown, pers. commun.). Yano (1911) also observed one colony to temporarily occupy a nest of Camponotus herculeanus japonicus in the ground while moving into a new nest in a bamboo fence. Kohriba (1963) put one female into the observation cage with 12 workers of Camponotus herculeanus japonicus after her nuptial flight. She was later accepted and her broods were tended by the host workers. The flight season is from late October to early November although male and female alates were also found in late July (Yano, 191 I). The chromosome numbers are n=21, 2n=42 (Imai, pers. commun.).

Ito et al. (2016) investigated the defensive function of petiole spines in queens and workers of this ant using the ant predating tree frog Hyla japonica. Ant workers have hook-like large spines on their petiole while the queen petiole has only small slightly curved spines. They found that intact workers of P. lamellidens are unpalatable while workers without spines and intact queens are palatable, indicating that the spines of workers provide an effective defense against the tree frogs.

Colony Founding
The following is a summery of observations made by Taku Shimada and reported on his blog site AntRoom between 2010 and 2015 (in Japanese, translated and summarised here). Observations were made both in the field as well as in laboratory colonies and involved numerous colonies collected over a number of years. Full details can be found at Colony Founding in Polyrhachis lamellidens.

The following steps seem essential for the successful establishment of a new nest by P. lamellidens queens:

1) The mated Polyrhachis lamellidens queen locates a nest of Camponotus japonicus.

2) A foraging C. japonicus worker is captured and subdued. The queen’s fore legs are used to transfer scent from the worker to her body.

3) The host nest is invaded and the C. japonicus queen is located.

4) The P. lamellidens queen attaches herself to the host queen's neck. They stay in close contact and transfer scent for up to 2 weeks. Host workers do not distinguish between the two queens and feed both.

5) The host queen is killed.

6) Workers feed the P. lamellidens queen over the winter period; her ovaries develop.

7) In spring, egg-laying begins with host workers tending the brood.

8) Over time, host workers die and are replaced with P. lamellidens workers. Eventually the colony becomes pure Polyrhachis lamellidens.

Feeding Biology
Polyrhachis lamellidens are omnivorous and will forage on a wide range of foods, including sap, aphid honeydew and dead insects and other arthropods. They are attracted to protein baits and when placed near the nest entrance large numbers of workers will recruit to the food source.

These ants have been observed feeding on a centipede. As they are not particularly strong hunters (for example, they lack a sting) it seems likely they were scavenging on a dead centipede rather than having captured a living one.

Other Ants

 * This species is a temporary parasite of (Kohriba, 1963),  (Sakai, 1990) and possibly  (Sakai, 1990).

Mesostigmatan Mites

 * Polyrhachis lamellidens workers are attacked by mesostigmatan mites that appear to specialise on ants. These mites show a strong preference to attach to the petiole as the majority of individuals have been observed in this position. The advantage of this placement is unclear, but it is likely the mites are either protected from removal by the ant or are attacking the soft tissue near the joint between the ant’s petiole and gaster.

Nomenclature

 *  lamellidens. Polyrhachis lamellidens Smith, F. 1874: 403 (w.) JAPAN. Donisthorpe, 1937a: 627 (q.); Koriba, 1963: 200 (l.); Wheeler, G.C. & Wheeler, J. 1970: 649 (l.); Hung, 1970: 29 (m.).

Worker
Hung (1970) - HW 1.70-2.08 mm, HL 1.88-2.25 mm, C1 84-94, SL 2.15-2.63 mm SI 122-134, PW 1. 10-1.50, mm, MPL 1.80-2.15 mm, MTL 2.65-3.08 mm, PSE1 140-233, PH 1.65-2.13 mm. Clypeus convex, with a sharp central longitudinal carina. No ocellus. Alitrunk margined with prominent ridges which are sharply interrupted at the pronounced promesonotal suture and the metanotal groove. Pronotum about as broad as long, its lateral ridge continued anteriorly on each side into a long spine, which is directed outward and forward and slightly curved downward at its tip. The spine is about as long as the pronotum. Mesonotum broader than long, bearing at the middle of each side a short rapidly tapering spine curved upward, outward and inclined backward. Propodeum about one-seventh longer than broad with ridge along the side extending posteriorly into a short, blunt spine which is about half the length of the propodeum. The ridge also continues down along the side of the declivity. Petiole columnar, anterior face convex, bearing a pair of 'long, somewhat flattened, hook-shaped spines, which diverge laterally and are inclined over the basal segment of the gaster. Gaster spherical with the tergite of the first segment covering almost half of the gaster. Mandibles, clypeus, occiput and legs with sparse, suberect hairs. Pubescence very sparse on the head and gaster, more abuudant on the pleurae and base of the gaster. Head very dusky red and finely shagreened. Alitrunk and petiole dark reddish-brown and punctate-rugulose. Gaster very dusky red and very shiny.

Kohout (2014) - (syntype cited first): TL c. 8.82, 7.31 – 9.07; HL 2.18 (head detached from the body), 1.78 – 2.18; HW 1.96, 1.56 – 1.96; CI 90, 88-90; SL 2.56, 2.09 – 2.65; SI 131, 130 – 136; PW 1.36, 1.03 – 1.36; PeH 1.76, 1.53 – 2.03; PeI 81, 81 – 94; MTL 3.02, 2.81 – 3.21 (1+18 measured).

Queen
Kohout (2014) - TL c. 10.08 – 10.63; HL 2.12 – 2.28; HW 1.75 – 1.87; CI 82 – 83; SL 2.31 – 2.40; SI 128 – 132; PW 2.03 – 2.18; PeH 1.18 – 1.31; PeI 53 – 62; MTL 2.87 – 3.12 (4 measured).

Male
Hung (1970) - Black and hairy with yellowish-brown hairs all over the body except the legs. Mandibles with pointed apex, masticatory border unarmed. Mesonotum convex, alitrunk without any spines. Petiolar spines short and tuberculate. Hind wing without discoidal cell. Genitalia with serrated lamina aedeagalis and pegged cuspis volsellaris and digitus volsellaris.

Larva
Immature stages described by Koriba (1963: 200) and Wheeler & Wheeler (1970: 649).

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