Skip to main content Skip to main navigation menu Skip to site footer
Published: 2022-03-03

Morphology of immatures of the thelytokous ant, Monomorium triviale Wheeler (Formicidae: Myrmicinae: Solenopsidini) with descriptions of the extraordinary last-instar queen larvae

Laboratory of Insect Ecology, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan.
Department of Biology, Faculty of Science and Engineering and Institute for Integrative Neurobiology, Konan University, 8-9-1 Okamoto, Higashinada-ku, Kobe, 658-8501, Japan.
Department of General Systems Studies, Graduate School of Arts and Sciences, The University of Tokyo, Komaba, Meguro, Tokyo 153-8902, Japan.
Hymenoptera larval morphology Pharaoh ant parthenogenesis phenotypic plasticity protuberance chaetotaxy


The ant genus Monomorium is one of the most species-rich but taxonomically problematic groups in the hyperdiverse subfamily Myrmicinae. An East Asian species, M. triviale Wheeler, produces both reproductive queens and sterile workers via obligate thelytokous parthenogenesis. Here, we describe the immature forms of M. triviale based on light and scanning electron microscopy observations, with a note on the striking caste dimorphism in the last larval instar. The last-instar queen larvae were easily recognized by their large size, “aphaenogastroid” body shape, and rows of doorknob-like tubercles on the lateral and dorsal body surface. This type of queen-specific structure has not been found in ants in general, let alone congeneric species found in Japan. In stark contrast to the queen larvae, worker larvae showed a “pheidoloid” body shape and a body surface similar to other ants. The worker larvae were estimated to have three instars, consistent with previously described congeners. The pupae of both castes had no cocoon, a characteristic commonly described in other Myrmicinae species. In total, the developmental period from egg to adult worker averaged 59 days under 25°C. We discuss possible functions of the tubercles of queen larvae based on previous studies.



  1. Adams, R.M.M., Larsen, R.S., Stylianidi, N., Cheung, D., Qiu, B., Murray, S.K., Zhang, G. & Boomsma, J.J. (2021) Hairs distinguish castes and sexes: identifying the early ontogenetic building blocks of a fungus-farming superorganism (Hymenoptera: Formicidae). Myrmecological News, 31, 201–216.
    Alvares, L.E., Bueno, O.C. & Fowler, H.G. (1993) Larval instars and immature development of a Brazilian population of pharaoh’s ant, Monomorium pharaonis (L.) (Hym., Formicidae). Journal of Applied Entomology, 116, 90–93.
    Bernard, F. (1955) Morphologie et comportement des fourmis lestobiotiques du genre Epixenus Emery. Insectes Sociaux, 2, 273–283.
    Bharti, H. & Gill, A. (2011) SEM studies on immature stages of Pheidole indica Mayr, 1879 (Hymenoptera: Formicidae) from India. Halteres, 3, 38–44.
    Bharti, H., Kaur, P. & Bharti, M. (2019) Description of the ant larvae of two species of the genus Myrmica Latreille, 1804 (Hymenoptera: Formicidae) from Indian Himalayas. Asian Myrmecology, 11, e011004.
    Bolton, B. (2021) An online catalog of the ants of the world. Available from: (accessed 31 October 2021)
    Casevitz-Weulersse, J. (1984) Les larves à expansions latérales de Crematogaster (Acrocoelia) scutellaris (Olivier) (Hym. Formicidae). Actes des Colloques Insectes Sociaux, 1, 131–138.
    Dussutour, A. & Simpson, S.J. (2009) Communal nutrition in ants. Current Biology, 19, 740–744.
    Edwards, J.P. (1991) Caste regulation in the pharaoh’s ant Monomorium pharaonis: recognition and cannibalism of sexual brood by workers. Physiological Entomology, 16, 263–271.
    Eidmann, H. (1926) Die ameisenfauna der balearen. Zoomorphology, 6, 694–742.
    Ettershank, G. (1965) A New Species of Megalomyrmex from the Chilean Andes (Formicidae, Hymenoptera). Psyche, 72, 55–58.
    Fox, E.G.P., Smith, A.A., Gibson, J.C. & Solis, D.R. (2017) Larvae of trap-jaw ants, Odontomachus LATREILLE, 1804 (Hymenoptera: Formicidae): morphology and biological notes. Myrmecological News, 25, 17–28.
    Gotoh, A., Billen, J., Hashim, R. & Ito, F. (2016) Degeneration patterns of the worker spermatheca during morphogenesis in ants (Hymenoptera: Formicidae). Evolution & Development, 18, 96–104.
    Gotoh, A., Billen, J., Tsuji, K., Sasaki, T. & Ito, F. (2012) Histological study of the spermatheca in three thelytokous parthenogenetic ant species, Pristomyrmex punctatus, Pyramica membranifera and Monomorium triviale (Hymenoptera: Formicidae). Acta Zoologica, 93, 200–207.
    Hölldobler, B. & Wilson, E.O. (1990) The Ants, Harvard University Press, Cambridge, MA, 732 pp.
    Idogawa, N., Sasaki, T., Tsuji, K. & Dobata, S. (2021) Comprehensive analysis of male-free reproduction in Monomorium triviale (Formicidae: Myrmicinae). PLoS ONE, 16 (4), e0246710.
    Ito, F., Makita, S., Nakao, H., Hosokawa, R., Kikuchi, T. & Yamane, S. (2021) Thelytokous parthenogenesis by dealate queens in the myrmicine ant Monomorium hiten distributed in Nansei Islands, western Japan, with description of the male. Asian Myrmecology, 14, e014001.
    Masuko, K. (1989) Larval hemolymph feeding in the ant Leptanilla japonica by use of a specialized duct organ, the “larval hemolymph tap” (Hymenoptera: Formicidae). Behavioral Ecology and Sociobiology, 24, 127–132.
    Masuko, K. (2017) Larval instars of the ant Strumigenys solifontis Brown (Hymenoptera: Formicidae): the fallacy of size distribution. Journal of Natural History, 51, 115–126.
    Masuko, K. (2019) Larval hemolymph feeding and hemolymph taps in the ant Proceratium itoi (Hymenoptera: Formicidae). Myrmecological News, 29, 21–34.
    Menozzi, C. (1930) Formiche della Somalia italiana meridionale. Memorie della Società Entomologica Italiana, 9, 76–130.
    Parra, J.R.P. & Haddad, G.M.L. (1989) Determinação do número de instares de insetos. Piracicaba, Fundação de Estudos, Agrários Luiz de Queiroz, 1989, 1–49.
    Peeters, C. & Hölldobler, B. (1992) Notes on the morphology of the sticky “doorknobs” of larvae in an Australian Hypoponera sp. (Formicidae; Ponerinae). Psyche, 99, 23–30.
    Penick, C.A., Copple, R.N., Mendez, R.A. & Smith, A.A. (2012) The role of anchor-tipped larval hairs in the organization of ant colonies. PLoS ONE, 7, e41595.
    Petralia, R.S. & Vinson, S.B. (1979) Comparative anatomy of the ventral region of ant larvae, and its relation to feeding behavior. Psyche, 86, 375–394.
    Pontieri, L. & Linksvayer, T.A. (2019) Monomorium. In: Encyclopedia of Social Insects. Springer International Publishing, Cham, pp. 1–6.
    Pontieri, L., Rajakumar, A., Rafiqi, A.M. & Larsen, R.S. (2020) From egg to adult: a developmental table of the ant Monomorium pharaonis. bioRxiv.
    Rajakumar, R., Koch, S., Couture, M., Favé, M.-J., Lillico-Ouachour, A., Chen, T., De Blasis, G., Rajakumar, A., Ouellette, D. & Abouheif, E. (2018) Social regulation of a rudimentary organ generates complex worker-caste systems in ants. Nature, 562, 574–577.
    R Core Team (2021) R: A Language and Environment for Statistical Computing. R Foundation for Statistical Computing, Vienna. Available from: (accessed 31 October 2021)
    Solis, D.R., Gonçalves Paterson Fox, E., Mayumi Kato, L., Massuretti de jesus, C., Teruyoshi Yabuki, A., Eugênia de Carvalho Campos, A. & Correa Bueno, O. (2010a) Morphological description of the immatures of the ant, Monomorium floricola. Journal of Insect Science, 10, 1–17.
    Solis, D.R., Fox, E.G.P., Rossi, M.L. & Bueno, O.C. (2010b) Description of the immatures of Linepithema humile Mayr (Hymenoptera: Formicidae). Biological Research, 43, 19–30.
    Schneider, C.A., Rasband, W.S. & Eliceiri, K.W. (2012) NIH Image to ImageJ: 25 years of image analysis. Nature Methods, 9, 671–675.
    Schultner, E., Oettler, J. & Helanterä, H. (2017) The role of brood in eusocial Hymenoptera. The Quarterly Review of Biology, 92, 39–78.
    Shattuck, S.O. (1992) Generic revision of the ant subfamily Dolichoderinae. Sociobiology, 21, 1–181.
    Sparks, K.S., Andersen, A.N. & Austin, A.D. (2019) A multi-gene phylogeny of Australian Monomorium Mayr (Hymenoptera: Formicidae) results in reinterpretation of the genus and resurrection of Chelaner Emery. Invertebrate Systematics, 33, 225–236.
    Taylor, R.W. (1965) A monographic revision of the rare tropicopolitan ant genus Probolomyrmex Mayr (Hymenoptera: Formicidae). Transactions of the Royal Entomological Society of London, 117, 345–365.
    Taylor, R.W. (1967) A monographic revision of the ant genus Ponera Latreille (Hymenoptera: Formicidae). Pacific Insects Monograph, 13, 1–112.
    Villet, M.H., Hanrahan, S.A. & Walther, C. (1990) Larval structures associated with larva-to-adult trophallaxis in Platythyrea (Hymenoptera : Formicidae). International Journal of Insect Morphology and Embryology, 19, 243–256.
    Ward, P.S., Brady, S.G., Fisher, B.L. & Schultz, T.R. (2015) The evolution of myrmicine ants: Phylogeny and biogeography of a hyperdiverse ant clade (Hymenoptera: Formicidae). Systematic Entomology, 40, 61–81.
    Wetterer, J.K. (2010a) Worldwide spread of the pharaoh ant, Monomorium floricola (Hymenoptera: Formicidae). Myrmecological News, 13, 19–27.
    Wetterer, J.K. (2010b) Worldwide spread of the pharaoh ant, Monomorium pharaonis (Hymenoptera: Formicidae). Myrmecological News, 13, 115–129.
    Wheeler, G.C. & Wheeler, J. (1955) The Ant Larvae of the Myrmicine Tribe Solenopsidini. American Midland Naturalist, 54, 119–141.
    Wheeler, G.C. & Wheeler, J. (1966) The Ant Larvae of the Subfamily Dolichoderinae: Supplement. Annals of the Entomological Society of America, 59, 726–732.
    Wheeler, G.C. & Wheeler, J. (1971) Ant larvae of the subfamily Ponerinae: second supplement. Annals of the Entomological Society of America, 64 (6), 1197–1217.
    Wheeler, G.C. & Wheeler, J. (1973) The ant larvae of six tribes: second supplement (Hymenoptera: Formicidae: Myrmicinae). Journal of the Georgia Entomological Society, 8:27–39.
    Wheeler, G.C. & Wheeler, J. (1976) Ant larvae: review and synthesis. Memoirs of the Entomological Society of Washington, 7, 1–108.
    Wheeler, G.C. & Wheeler, J. (1980) Supplementary Studies on ant Larvae: Ponerinae, Myrmicinae and Formicinae. Transactions of the American Entomological Society, 106, 527–545.
    Wheeler, W.M. (1918) A study of some ant larvae, with a consideration of the origin and meaning of the social habit among insects. Proceedings of the American Philosophical Society, 57, 293–343.