Leptogenys chalybaea

Leptogenys chalybaea
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Hymenoptera
Family:	Formicidae
Subfamily:	Ponerinae
Tribe:	Ponerini
Genus:	Leptogenys
Species group:	chalybaea
Species:	L. chalybaea
Binomial name
Leptogenys chalybaea (Emery, 1887) Specimen Labels

A member of a small complex of SE Asian Leptogenys species (L. chalybaea species group, Arimoto & Yamane 2018). In Cambodia, Thailand and Vietnam workers of species in this group have been observed linking their bodies in chains during the retrieval of freshly immobilized large millipedes (see below, the Leptogenys cyanicatena species page and Peeters & De Greef, 2015). Chains are a striking example of cooperation in ants, and this behavior is a novel method of prey transport.

Identification

Arimoto and Yamane (2018) - A member of the Leptogenys chalybaea species group. Worker: Mandible with basal angle bluntly angular; basal margin slightly concave near basal angle; masticatory margin straight, but curved ventrad near apex. Eye length in full-face view less than one-fourth of head lateral margin length; eye outer margin close to lateral outline of head. Apex of clypeal median lobe with two peg-like setae. Anterior lobe of subpetiolar process posteroventrally with acute tooth. Body blue and with metallic luster. Head nearly mostly smooth, but anterior part of frons and gena weakly longitudinally striate. Mesosternum with few transverse striae. Petiole smooth, sometimes with few longitudinal to oblique striae. Gaster smooth.

Keys including this Species

• Key to Leptogenys chalybaea species group workers
• Key to Oriental Leptogenys

Distribution

The most recent examination of the distribution of this species (Arimoto and Yamane 2018) determined this species is known from East Malaysia (Borneo): Sarawak, Sabah. Additional occurrence data from other locations are not believed to be this same species.

Latitudinal Distribution Pattern

Latitudinal Range: 4.533333333° to 2.547988°.

North Temperate	North Subtropical	Tropical	South Subtropical	South Temperate

• Source: AntMaps

Distribution based on Regional Taxon Lists

Indo-Australian Region: Borneo, Indonesia, Malaysia (type locality).

Distribution based on AntMaps

Distribution based on AntWeb specimens

Check data from AntWeb

Countries Occupied

Number of countries occupied by this species based on AntWiki Regional Taxon Lists. In general, fewer countries occupied indicates a narrower range, while more countries indicates a more widespread species.

Estimated Abundance

Relative abundance based on number of AntMaps records per species (this species within the purple bar). Fewer records (to the left) indicates a less abundant/encountered species while more records (to the right) indicates more abundant/encountered species.

Biology

Arimoto and Yamane (2018) - Leptogenys chalybaea was observed nesting in soil under a rock and foraging on the forest floor in Borneo, Malaysia. The hunting behavior of this species has not been observed. The ecology of this species is thought to be similar to that of Leptogenys cyanicatena (as described on the L. cyanicatena species page, in Peeters & De Greef, 2015 and below) due to their similar morphology.
Daisy chain blue ants killing giant millipede in Cambodia. Video © Stéphane De Greef, used with permission.

Peeters & De Greef (2015) - Chain behaviour in L. cyanicatena functions for the collective transport of large millipedes. This bluish species is a swarm raider with a small range of prey: millipedes belonging to four orders, and occasional earthworms. Small prey were carried individually or dragged by a few ants, while chains made it possible to move millipedes weighing up to 16.4 g. Chains (either linear or branched) changed according to obstacles along the way to the nests. Between 2 and 52 workers were observed to drag single prey items, with only a few ants directly grasping the prey. One 15-cm-long millipede was captured rodeo-style after being encircled by 25–30 ants. As it uncurled from a defensive coil, the ants held back except one that tried to sting between its legs. The millipede started thrashing about which caused many ants to attempt stinging.

Workers of Leptogenys cyanicatena assemble in chains to drag a heavy millipede (order Spirostreptida, 15 cm-long, 16.4 g fresh weight). From Siem Reap province, Cambodia. Photograph © Stéphane De Greef, used with permission.

Many species of Leptogenys with large workers occur in Africa and the Neotropics (Bolton 1975; Lattke 2011), while large millipedes are also distributed on these continents. Yet chain behavior has never been reported outside SE Asia, suggesting that its evolution requires a complex combination of traits (Peeters & De Greef 2015). Four other ponerine genera hunt millipedes solitarily, but chains are not used.

Detail of short linear chain used to drag a smaller millipede (order Spirobolida, 1.9 g fresh weight). Photograph © Stéphane De Greef, used with permission.

Single foragers of Leptogenys sp. retrieving a pill millipede (order Sphaerotheriida). Photograph © Stéphane De Greef, used with permission.

Castes

Images from AntWeb

Worker. Specimen code casent0281931. Photographer Shannon Hartman, uploaded by California Academy of Sciences.	Owned by NHMUK, London, UK.

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Images from AntWeb

Syntype of Leptogenys chalybaea. Worker. Specimen code casent0903954. Photographer Will Ericson, uploaded by California Academy of Sciences.	Owned by MSNG, Genoa, Italy.

Nomenclature

The following information is derived from Barry Bolton's Online Catalogue of the Ants of the World.

• chalybaea. Lobopelta chalybaea Emery, 1887b: 432 (w.) BORNEO. Combination in Leptogenys (Lobopelta): Emery, 1911d: 102.

Unless otherwise noted the text for the remainder of this section is reported from the publication that includes the original description.

Description

Worker

Arimoto and Yamane (2018) - (n=5, lectotype in parentheses). HL: 2.22–2.47 (2.44), HLL: 1.82–2.04 (2.04), HLA: 0.75–0.89 (0.89), HW: 1.68–1.94 (1.94), CML: 0.44–0.55 (0.55), CI: 75–80 (79), CLI: 20–23 (23), SL: 2.52–2.82 (2.72), SI: 140–152 (140), EL: 0.41–0.47 (0.47), OI: 22–24 (23), PrL: 1.39–1.53 (1.46), PrH: 0.92–1.10 (0.93), PrW: 1.33–1.51 (1.48), WL: 3.74–4.03 (4.00), PeL: 0.99–1.12 (1.12), PeH: 1.27–1.41 (1.36), PeW: 0.86–1.02 (1.02), LPI: 121–129 (121), DPI: 87– 95 (95).

Head width in full-face view less than 0.8 times as long as its length. Mandible with basal angle bluntly angular, sometimes rounded; basal margin slightly concave near basal angle; masticatory margin straight, but curved ventrad near apex. Eye length in full-face view less than one-fourth of head lateral margin length; outer margin close to lateral outline of head. Antennal scape surpassing posterior head margin by more than two-fifths its length; antennomere XII approximately 2.7 times as long as wide. Clypeus without longitudinal median carina; apex of clypeal median lobe with two peg-like setae. Pronotum in dorsal view shorter to longer than wide. Propodeal dorsum in profile almost straight; declivity separated from dorsum by blunt angle, concave and approximately half of length of dorsum; propodeal spiracle elliptical. Petiole in dorsal view distinctly longer than wide. Anterior lobe of subpetiolar process posteroventrally with acute tooth. Head nearly mostly smooth, but anterior part of frons, and gena weakly longitudinally striate. Head posterior to eye with scalloped depressions, which shallowly impressed posterolaterally and sloping anteromedially. Mandible with longitudinal to oblique striae. Antennal scape smooth basally and becoming weakly imbricate apicad. Clypeus smooth, but with few longitudinal to oblique striae near anterior margin. Mesosoma mostly with weak oblique to longitudinal striae; anteroventral margin of mesopleuron with distinct transverse coarse costulae; prododeal dorsum with scalloped depressions, which shallowly impressed anteriorly and sloping posteriorly; propodeal side medially smooth; propodeal declivity transversely striate. Meso-metapleural suture well impressed, broad and scrobiculate. Metapleuro-propodeal suture impressed and narrow. Mesosternum with few transverse striae. Coxa smooth. Petiole smooth, but node sometimes with few longitudinal to oblique striae; subpetiolar process with slight alveolate. Gaster smooth; anterior margin of gastral segments II with a brief scrobiculate band. Body dark-blue to light-blue and with metallic luster. Antennal scape dark-blue; antennomeres II–XII red-brown, sometimes antennomeres II–IV blackish. 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; tarsi red-brown. Ventral half of petiole and gastral sternites blackish. Hairs yellow-brown. Antennal scape with dense short pubescence and with sparse erect long hairs. Erect hairs moderate in density on dorsum of body.

Queen

Arimoto and Yamane (2018) - (n=2). HL: 2.11–2.19, HLL: 1.74-1.80, HLA: 0.76, HW: 1.69–1.74, CML: 0.47-0.49, CI: 79–80, CLI: 22, SL: 2.24–2.33, SI: 133–134, EL: 0.37-0.38, OI: 20-21, PrL: 0.85-0.96, PrH: 0.85-0.96, PrW: 1.22-1.23, WL: 3.35–3.38, PeL: 0.90–1.00, PeH: 1.44–1.48, PeW: 0.76–0.78, LPI: 144-164, DPI: 76–86. Propodeal declivity separated from dorsum by blunt angle. Petiolar node high rectangular in profile; anterior margin parallel in posterior margin; dorsal margin truncate. Anterior lobe of the petiolar process with rounded posteroventral angle. Petiole and gaster smooth. Subpetiolar process with slight alveolate.

Type Material

• Lectotype (designated by Arimoto and Yamane, 2018: 20), worker, Sarawak, Malaysia, 1865–1866, Giacomo Doria and Odoardo Beccari, LCB001, Museo Civico di Storia Naturale, Genoa; Detailed collecting locality of the types is unknown. One of the collectors (O. Beccari) is not indicated on the data labels, but mentioned in the original description..
• Paralectotype (designated by Arimoto and Yamane, 2018: 20), 1 queen, Sarawak, Malaysia, 1865–1866, Giacomo Doria and Odoardo Beccari, LCB002, ANTWEBCASENT0903954, Museo Civico di Storia Naturale, Genoa.

Determination Clarifications

Arimoto and Yamane (2018) - Mayr (1872) recorded Lobopelta iridescens (Smith, 1858) from Borneo; however, the specimen had been misidentified. This species was described as Lobopelta chalybaea Emery 1887 from Sarawak, Malaysia. Subsequently, it has been treated as Leptogenys chalybaea, after which Lobopelta was synonymized with Leptogenys (Bolton, 1995). Leptogenys chalybaea has also been recorded from Thailand (Jaitrong and Nabhitabhata, 2005), but that specimen was also misidentified. The Thailand species closely resembles Leptogenys chalybaea; however, they can be distinguished by the configuration of the mandible and eye, clypeus, and body sculpture (see notes for Leptogenys cyanicatena). Therefore, we determined that the Thailand species remains undescribed

References

• Arimoto, K., Yamane, S. 2018. Taxonomy of the Leptogenys chalybaea species group (Hymenoptera, Formicidae, Ponerinae) from Southeast Asia. Asian Myrmecology 10, e010008 (DOI 10.20362/am.010008).
• Emery, C. 1887e. Catalogo delle formiche esistenti nelle collezioni del Museo Civico di Genova. Parte terza. Formiche della regione Indo-Malese e dell'Australia (continuazione e fine). [part]. Ann. Mus. Civ. Stor. Nat. 25[=(2)(5): 427-432 (page 432, worker described)
• Emery, C. 1911e. Hymenoptera. Fam. Formicidae. Subfam. Ponerinae. Genera Insectorum 118: 1-125 (page 102, Combination in Leptogenys (Lobopelta))
• Peeters, C. & De Greef, S. 2015. Predation on large millipedes and self-assembling chains in Leptogenys ants from Cambodia. Insectes Sociaux 62: 471-477.
• Satria, R., Nugraha, F.A.D., Achyar, A., Zulyetti, D., Eguchi, K. 2024, Description of the male caste of Leptogenys borneensis (Hymenoptera, Formicidae), with its first discovery in Sumatra. Zoodiversity 58 (1), 19-26 (doi:10.15407/zoo2024.01.19).
• Yamane, S., Tanaka, H.O., Hasimoto, Y., Ohashi, M., Meleng, P., Itioka, T. 2021. A list of ants from Lambir Hills National Park and its vicinity, with their biological information: Part II. Subfamilies Leptanillinae, Proceratiinae, Amblyoponinae, Ponerinae, Dorylinae, Dolichoderinae, Ectatomminae and Formicinae. Contributions from the Biological Laboratory, Kyoto University 31, 87–157.

References based on Global Ant Biodiversity Informatics

• Arimoto K., and S. Yamane. 2018. Taxonomy of the Leptogenys chalybaea species group (Hymenoptera, Formicidae, Ponerinae) from Southeast Asia. Asian Myrmecology 10: e010008.
• Bakhtiar E.Y., and S.L. Chiang. 2010. Leptogenys ants (Hymenoptera: Formicidae: Ponerinae) of Sabah. Serangga 15(1-2): 37-55.
• Chapman, J. W., and Capco, S. R. 1951. Check list of the ants (Hymenoptera: Formicidae) of Asia. Monogr. Inst. Sci. Technol. Manila 1: 1-327
• Davidson D. W., S. C. Cook, R. R. Snelling and T. H. Chua. 2003. Explaining the Abundance of Ants in Lowland Tropical Rainforest Canopies. Science 300: 969-972.
• Emery C. 1887. Catalogo delle formiche esistenti nelle collezioni del Museo Civico di Genova. Parte terza. Formiche della regione Indo-Malese e dell'Australia (continuazione e fine). [concl.]. Ann. Mus. Civ. Stor. Nat. 25(5): 427-473.
• Emery C. 1911. Hymenoptera. Fam. Formicidae. Subfam. Ponerinae. Genera Insectorum 118: 1-125.
• Emery, C.. "Catalogo delle formiche esistenti nelle collezioni del Museo Civico di Genova. Parte terza. Formiche della regione Indo-Malese e dell'Australia (continuazione e fine)." Annali del Museo Civico di Storia Naturale Giacomo Doria (Genova) (2) 5, no. 25 (1887): 427-473.
• Jaitrong W.; Nabhitabhata, J. 2005. A list of known ant species of Thailand. The Thailand Natural History Museum Journal 1(1): 9-54.
• Pfeiffer M.; Mezger, D.; Hosoishi, S.; Bakhtiar, E. Y.; Kohout, R. J. 2011. The Formicidae of Borneo (Insecta: Hymenoptera): a preliminary species list. Asian Myrmecology 4:9-58
• Wheeler W. M. 1919. The ants of Borneo. Bulletin of the Museum of Comparative Zoology 63:43-147.