Leptogenys cyanicatena

In Cambodia, workers link their bodies in chains during the retrieval of freshly immobilized large millipedes (see below, the Leptogenys chalybaea species page and Peeters & De Greef 2015). Chains are a striking example of cooperation in ants, and is a novel method of prey transport. In Thailand, 2-3 workers can retrieve shorter millipedes, and short chains have been observed when obstacles are encountered (Peeters & Mizuno unpublished)

Identification
Arimoto and Yamane (2018) - A member of the Leptogenys chalybaea species group. Mandible with bluntly angular basal angle; basal margin slightly concave near basal angle; masticatory margin weakly convex near basal angle. Eye length in full-face view more than one-fourth of head lateral margin length; outer margin just breaking lateral outline of head. Apex of clypeal median lobe with three peg-like setae. Anterior lobe of subpetiolar process posteroventrally with acute tooth. Body blue and with metallic luster. Head, mesosoma, and petiolar node distinctly rugose, but anterior part of frons, and gena longitudinally striate; gaster smooth except for longitudinally striate gastral segments I-II.

Leptogenys cyanicatena is clearly similar to Leptogenys chalybaea in having a blue body with metallic luster, but is differentiated from Leptogenys chalybaea by the following contrasting characters of the worker and queen castes (Leptogenys chalybaea in parentheses): masticatory margin of mandible weakly convex near basal angle (straight, but curved near apex); eye larger (OI: 27–28 in worker, 27–30 in queen) (smaller, OI: 22–24 in worker, 20–21 in queen); outer margin of eye in full-face view just breaking lateral outline of head (close to lateral outline of head); head rugose (smooth, partly striate), mesosoma and petiole rugose (striate); gastral segments I–II longitudinally striate in worker or with finely alveolate in queen.

Specimens from north Thailand were paler in color than specimens from other locations.

Distribution
Arimoto and Yamane (2018) - Laos: Vientiane. Thailand: Chiang Mai, Kanchanaburi, Phetchaburi, Nakhon Ratchasima, Chacheongsao, Chonburi, Chantaburi. Cambodia: Siem Reap. Myanmar (personal communication with Dr. C. Peeters).

Distribution based on type material
Thailand.

Biology
Highly specialised millipede hunters​. In Thailand, g​roups of 20-30 workers, ​recruited and ​led by one scout​, go out to subdue and retrieve single millipedes. Depending on the size of prey that needs to be dragged back to nest, they use chains or not.

Arimoto and Yamane (2018) - Many workers of a colony (AK75) in Cambodia were observed cooperatively hunting a large millipede (Spirostreptida). This colony used an abandoned termite nest as its nest in the forest. The colony was too large to collect in its entirety, but we estimated that it contained about 1,000 individuals. A colony (AK119) in Eastern Thailand was observed cooperatively hunted a small millipede (Sphaerotheriida). Another colony (AK142) from Eastern Thailand nested on a large ceramic plate left in a grassland at the edge of a forest. The colony was composed of one mated queen, 44 virgin queens, 371 workers, 36 pupae, 225 larvae, and 457 eggs. This nest did not contain any males, and was probably premature. Exoskeletons of millipedes (Spirostreptida) were also found in the nest.

This species has a small range of prey: millipedes belonging to four orders (Polydesmida, Spirostreptida, Spirobolida, and Sphaerotheriida) and earthworms (Peeters and De Greef, 2015).

Nomenclature

 *  cyanicatena. Leptogenys cyanicatena Arimoto and Yamane, 2018: 22, figs. 3, 10–14, 15C, F, 16E, F (w.q.) THAILAND.

Worker
(n=5, holotype in parentheses). HL: 2.52–2.68 (2.66), HLL: 2.07–2.19 (2.19), HLA: 0.90–1.01 (1.01), HW: 2.06–2.18 (2.17), CML: 0.51–0.60 (0.60), CI: 81–82 (0.81), CLI: 20–23 (23), SL: 2.76–2.97 (2.94), SI: 134–136 (135), EL: 0.55–0.60 (0.58), OI: 27–28 (27), PrL: 1.51–1.58 (1.51), PrH: 1.03–1.17 (1.14), PrW: 1.51–1.59 (1.54), WL: 4.00–4.10 (4.10), PeL: 1.02–1.07 (1.07), PeH: 1.46–1.55 (1.47), PeW: 0.95–1.05 (0.95), LPI: 137–151 (138), DPI: 89– 102 (89).

Head width in full-face view approximately 0.8 times as long as its length. Mandible with bluntly angular basal angle; basal margin slightly concave near basal angle; masticatory margin weakly convex near basal angle. Eye length in full-face view more than one-fourth of head lateral margin length; outer margin just breaking lateral outline of head. Antennal scape surpassing posterior head margin by more than two-fifths its length; antennomere XII approximately 2.6 times as long as wide. Clypeus with longitudinal median carina, sometimes the carina undefined; apex of clypeal median lobe with three peg-like setae. Pronotum in dorsal view slightly longer than wide, sometimes slightly shorter than wide. Propodeal dorsum in profile broadly conHead width in full-face view approximately 0.8 times as long as its length. Mandible with bluntly angular basal angle; basal margin slightly concave near basal angle; masticatory margin weakly convex near basal angle. Eye length in full-face view more than one-fourth of head lateral margin length; outer margin just breaking lateral outline of head. Antennal scape surpassing posterior head margin by more than two-fifths its length; antennomere XII approximately 2.6 times as long as wide. Clypeus with longitudinal median carina, sometimes the carina undefined; apex of clypeal median lobe with three peg-like setae. Pronotum in dorsal view slightly longer than wide, sometimes slightly shorter than wide. Propodeal dorsum in profile broadly convex; declivity concave to almost straight, forming continuous curve, sometimes separated from dorsum by blunt angle; declivity two-fifths length of dorsum; propodeal spiracle elliptical. Petiole in dorsal view longer than wide, sometimes slightly shorter than wide. Anterior lobe of subpetiolar process posteroventrally with acute tooth.

Head, mesosoma, and petiolar node distinctly rugose; anterior part of frons and gena longitudinally striate. Mandible with fine longitudinal striae near basal margin. Antennal scape slightly alveolate basally and becoming distinctly imbricate apicad. Clypeus with oblique to longitudinal striae. Meso-metapleural suture well impressed and wide, posteriorly with rugose sculpture. Metapleuro-propodeal suture well impressed. Mesosternum smooth. Coxa finely alveolate. Petiolar node with well-impressed scalloped depressions; lateral face of petiolar node with longitudinal striae. Ventral half of petiole and gastral segments III–V smooth but partly with slight alveolate. Gastral segments I–II longitudinally striate. Anterior margin of gastral segments II with a brief scrobiculate band.

Body dark-blue and with metallic luster. Antennal scape dark-blue; antennomere II red-brown; antennomeres III–XII black and apically red-brown. Mandible and clypeus dark-red; median lobe of clypeus tinged with blue and with metallic luster. Coxa, femur and tibia dark-blue, tinged with red; tarsus red-brown. Ventral half of petiole and gastral sternites blackish. Hairs red-brown. Antennal scape moderately with short pubescence and sparsely with erect long hairs. Erect hairs moderate in density on dorsum of body.

Queen
(n=5). HL: 2.40–2.49, HLL: 1.95–2.04, HLA: 0.84–0.92, HW: 1.91–1.98, CML: 0.50–0.57, CI: 79–80, CLI: 21–23:, SL: 2.33–2.59, SI: 122–133, EL: 0.55–0.60, OI: 27–30, PrL: 1.31–1.43, PrH: 0.96–1.15, PrW: 1.38–1.45, WL: 3.61–3.77, PeL: 0.95–1.00, PeH: 1.73–1.77, PeW: 0.72–0.77, LPI: 174–185, DPI: 75–81. Propodeal dorsum and declivity forming a continuous curve. Petiolar node in profile high trapezoidal, narrowed dorsally; dorsal margin convex. Anterior lobe of the petiolar process with acute posteroventral angle. Petiole and gastral segments I-II finely alveolate. Scrobiculate band of gastral segments II with finely alveolate sculpture. Gastral segments III–V smooth.

Head in full-face view distinctly longer than wide; posterior margin distinctly prominent. Mandible without basal angle and teeth apex rounded. Compound eye occupies three-fifths of head length. Ocelli large; maximum length of lateral ocellus greater than minimum distance between lateral ocellus and eye. Antenna 13 segmented; scape less than half of head width; antennomere II shortest; III longer than scape; XIII more than 1.5 times as long as XII. Clypeus roughly keeled on midline; anterior margin broadly convex; anterior lateral margin with narrow translucent lamella. Mesoscutum in dorsal view longer than wide, widest posterior to mid-length, in profile strongly convex; notaulus weakly impressed; length of parapsidal line more than half of mesoscutal length; transscutal line almost straight to slightly curved. Metapleuro-propodeal sulcus present. Propodeal dorsum and declivity forming continuous curve; propodeal spiracle circular. Forewing approximately 2.9 times as long as wide, approximately 1.2 times as long as hindwing length; vein Sc+R+Rs often connected with costal vein, sometimes not connected; with stigma. Hindwing approximately 3.6 times as long as wide. Petiole in profile higher than long, in dorsal view longer than wide; node in profile subtrapezoidal, with anterior margin inclined posterad, with posterior margin inclined anterad; in dorsal view lateral margin convex; anterior, dorsal, and posterior margins almost straight to slightly convex. Anterior lobe of subpetiolar process in profile broadly rectangular, with posteroventral right angle; posterior extension thin, broadly and smoothly curved between anterior lobe. Prora small, pointed ventrally, separated from anteroventral angle of gastral sternite I by distinct indentation.

Head and propodeum roughly rugose. Mandible and clypeus smooth. Pronotum longitudinally striate. Mesoscutum smooth anteriorly and transversely striate posteriorly. Mesoscutellum longitudinally striate. Mesopleuron with few striae. Scutoscutellar sulcus longitudinally striate. Petiole smooth; dorsal margin with a median longitudinal striae. Constriction between gastral segments I and II scrobiculate; gastral segments I–II almost smooth but weakly and very finely alveolate; III–V smooth.

Body black, tinged with red and with blue luster; clypeus, mandible, antennae and legs red-brown. Hairs yellow-brown, erect. Antennal scape with dense short pubescence and erect long hairs; antennomeres II–XIII densely covered with short pubescence. Erect hairs of gastral sternites denser than those of tergites.

Type Material
Holotype: Worker (AK75), Siem Reap District, Siem Reap Province, North Cambodia, 13.4° N, 103.9° E, 40 m, 24 VIII 2012, Kôichi Arimoto leg. [; LCC001].

Paratypes: (120 workers, 2 mated queens, 22 virgin queens, 15 males). LAOS. 1 worker, forager on road, Sivilay Village, Naxaithong District, Vientiane Prefecture, Laos, 220 m, 18°15′ N, 102°27′ E, 9 VI 2010, Seiki Yamane leg. [; LCC002]. THAILAND. 20 workers (MM43), near Accomodation, Doi Suthep, Chiang Mai Province, North Thailand, 18°48’34” N, 98°54’57” E, 1,200m, 11 VII 2014, Munetoshi Maruyama leg. [DNPT; LCC003 to LCC022]; 7 workers, 1 virgin queen (TH02-SKY-07), Srinakarin Dam National Park, Kanchanaburi Province, West Thailand, 150–200 m, 29 VI 2002, Seiki Yamane leg. [SKYC; workers: LCC023 to LCC029; virgin queen: LCC030]; 15 workers, 1 virgin queen (TH-02-SKY-15), same place as the former, 29 VI 2002, Seiki Yamane leg. [SKYC; worker: LCC031 to LCC045; virgin queen: LCC046]; 8 workers (TH14-SKY-92), Kaeng Krachan National Park, Phetchaburi Province, West Thailand, 28 VI 2014, Sasitorn Hasin & Maruyama Maruyama leg. [SKYC; LCC047 to LCC054]; 7 workers, (TH99-SKY-22), Dry evergreen forest, lowland, Sakaerat Envirinmental Reserch Station, Nakhon Ratchasima Province, Northeast Thailand, 10 VII 1999, Seiki Yamane leg. [SKYC; LCC055 to LCC061]; 8 workers (TH03-SKY-26), Dry evergreen forest, Lumchangwat Station, Khao Ang Rue Nai Wild Sanctuary, Chacheongsao Province, East Thailand, 21 VIII 2003, Seiki Yamane leg. [SKYC; LCC062 to LCC069]; 3 workers, same place as the former, 22 VIII 2003, Seiki Yamane leg. [SKYC; LCC070 to LCC072]; 10 workers (AK119), Bang Phra, Si Racha, Chonburi Province, East Thailand, 13.20° N, 100.95° E, 220 m, 13 VI 2013, Kôichi Arimoto leg. [; LCC073 to LCC082]; 30 workers, 1 mated queen, 15 virgin queens (AK142), Krathing Country Resort, Pluang, Khao Khitchakut, Chantaburi Province, East Thailand, 12.82° N, 102.13° E, 90 m, 8 III 2014, Kôichi Arimoto leg. [KUEC; workers: LCC083 to LCC112; mated queen: LCC113; virgin queens: LCC114 to LCC128; 5 workers and 3 virgin queens donated to BMNH (LCC103 to LCC107, LCC123 to LCC125), 5 workers and 3 virgin queens donated to MSNG (LCC108 to LCC112, LCC126 to LCC128)]. CAMBODIA. 1 worker (AK69), Siem Reap District, Siem Reap Province, North Cambodia, 22 VIII 2012, Kôichi Arimoto leg. [KUEC; LCC129]; 10 workers, 1 mated queen, 5 virgin queens, 15 males (AK75), same colony as the holotype [KUEC; workers: LCC130 to LCC139; mated queen: LCC140; virgin queens: LCC141 to LCC 145; males: LCC146 to LCC160].

Etymology
The combination of the Latin cyaneus, meaning dark blue, and the Latin catena, meaning chain, refers to chain behavior for the collective transport of large millipedes.

Determination Clarifications
Leptogenys cyanicatena was originally recorded as Leptogenys chalybaea (Emery, 1887) from Thailand (Jaitrong and Nabhitabhata, 2005).