The taxon was revised as a subgenus by Hosoishi and Ogata (2009). Much of what is found on this page is based on their revision.
- Crematogaster ampullaris
- Crematogaster aurita
- Crematogaster bakeri
- Crematogaster difformis
- Crematogaster inflata
- Crematogaster mucronata
- Crematogaster onusta
- Crematogaster physothorax
- Crematogaster sewardi
- Crematogaster tanakai
- Crematogaster vacca
- Crematogaster yamanei
Workers of the subgenus Physocrema can be distinguished from those of all other subgenera of Crematogaster by the features of (1) anteromedian margin of clypeus convex with slightly impressed median portion; (2) anterolateral margins of clypeus produced anteriorly; (3) 4-jointed antennal club (but, 3-jointed in mucronata); (4) propodeum swollen; (5) metapleural gland orifice circular; (6) petiole elliptical; (7) petiole without node-like process posteriorly. The subgenus is unique among Asian Crematogaster ants in having features (4), (5), (6) and (7). The workers of the subgenus Physocrema share features (1), (2), (3) and (7) with the subgenus Paracrema. In Asian Crematogaster specimens examined, the workers of the subgenera Crematogaster, Decacrema, Mesocrema, Oxygyne, Paracrema, Physocrema and Xiphocrema share features (2) and (7).
Most Physocrema species show strong polymorphism in size and sculpture and it is especially pronounced in C. (P.) ampullaris, C. (P.) aurita, C. (P.) difformis, C. (P.) sewardi, C. (P.) yamanei and C. (P.) vacca, and weakly so in C. (P.) inflata, C. (P.) mucronata, C. (P.) onusta and C. (P.) physothorax. In the especially pronounced group, small workers are very different from large workers. For example, in C. (P.) aurita, the scape clearly exceeds the posterior corner of the head in small workers, but it does not in large workers. In general, the mandible has 5 teeth on the masticatory margin, but in some species smaller specimens have only 4 teeth. The postpetiole lacks a longitudinal median sulcus, but it is weakly bilobed posteriorly in large workers of some species. To diagnose Physocrema species, large workers are more useful than smaller workers, particularly in closely similar species.
Southeast Asia: Vietnam (southern parts), Laos, Cambodia, Thailand, Myanmar (southeastern parts), Malaysia (Peninsula and Borneo), Singapore, Indonesia (Sumatra, Mentawai, Java, Bali, Lombok, Kalimantan, Sulawesi, Timor), Philippines.
Workers in some Physocrema species release defensive secretions from their metapleural glands when they are disturbed (Bushinger & Maschwitz, 1984). Two arthropods were reported to be possible Batesian mimics of Crematogaster inflata, because of the defensive mechanism. A Camponotus ant nests and forages near the nest of C. (P.) inflata and has similar body coloring pattern and walking behavior (Ito et al. 2004). The other is a staphylinid beetle, Drusilla inflatae, collected near colonies of C. (P.) inflata (Maruyama et al. 2003). The color pattern of the beetle closely resembles that of C. (P.) inflata. The secretions contain a mixture of phenols in Crematogaster difformis and C. (P.) inflata (Attygalle et al. 1989; Jones et al. 2005). Jones et al. (2005) suggest that analyses of the secretions may be useful for taxonomic and phylogenetic studies.
Some species of the subgenus Physocrema are reported to be mutualistic ants in ant plants. Several Lecanopteris fern species are inhabited by these ants in Malay Peninsula, Borneo, Sumatra and Sulawesi (Gay & Hensen, 1992). The rubiaceous tree, Neonauclea cyrtopoda, was occupied by these ants in North Sumatra (Maschwitz & Fiala, 1995). The authors identified the black Crematogaster ants with an inflated propodeum as C. (P.) difformis, but those identifications are doubtful because of the similar species. The reported associations were probably opportunistic, and there is no indication that any species of Physocrema form obligate associations with ant plants. This study should facilitate future studies of mimicry and mutualism.
The following information is derived from Barry Bolton's New General Catalogue, a catalogue of the world's ants.
- PHYSOCREMA [junior synonym of Crematogaster (Crematogaster)]
- Physocrema Forel, 1912f: 220 [as subgenus of Crematogaster]. Type-species: Crematogaster inflata, by subsequent designation of Wheeler, W.M. 1913a: 82.
- Physocrema raised to genus: Soulié, 1964: 398.
- Physocrema junior synonym of Crematogaster: Hölldobler & Wilson, 1990: 13.
- Physocrema subgenus of Crematogaster: Bolton, 1995b: 42.
- Physocrema junior synonym of Crematogaster (Crematogaster): Blaimer 2012: 53.
Hosoishi and Ogata (2009) - Diagnosis of worker. Head subquadrate, slightly broader than long, with weakly concave posterior margin, angular posterior corners and subparallel sides. Occipital carinae developed. Mandible striate, with four teeth in small workers and five in larger workers, apical and subapical teeth large. Anterior margin of clypeus convex with slightly impressed median portion (Figs 1, 2); anterolateral margins of clypeus protruded anteriorly, resulting in an appearance of the anterolateral and anteromedian margins being at about the same level (Figs 1, 2); posterior margin of clypeus rounded between frontal lobes. Frontal carinae almost parallel. Antennae 11 segmented; antennal club 4-jointed. Compound eyes large but not distinctly projecting beyond lateral margins of head in full face view.
Pronotum and mesonotum usually without defined suture, rarely promesonotal suture present in large workers. Mesothoracic spiracle reduced to form small pit dorsoventrally. Variable extent of posterior mesosoma enlarged and swollen (Figs 3, 4). Metapleural gland opening circular; propodeal spiracle facing posterolaterally (Figs 3, 4).
Petiole flattened without node nor subpetiolar process; spiracle situated anteriorly midway between dorsal and ventral margins of petiole in lateral view, directed laterally; in dorsal view, elliptical with convex sides, longer than broad (Fig. 5). Postpetiole without distinctly longitudinal median sulcus, weakly bilobed behind in large workers (Fig. 5); spiracle situated distinctly anteriorly on the lateral surface.
- Blaimer, B.B. 2012. A subgeneric revision of Crematogaster and discussion of regional species-groups (Hymenoptera: Formicidae). Zootaxa 3482, 47–67.
- Bolton, B. 1995b. A new general catalogue of the ants of the world. Cambridge, Mass.: Harvard University Press, 504 pp. (page 42, Physocrema subgenus of Crematogaster)
- Bolton, B. 2003. Synopsis and Classification of Formicidae. Mem. Am. Entomol. Inst. 71: 370pp (page 239, Physocrema as subgenus of Crematogaster)
- Brown, W. L., Jr. 1973b. A comparison of the Hylean and Congo-West African rain forest ant faunas. Pp. 161-185 in: Meggers, B. J., Ayensu, E. S., Duckworth, W. D. (eds.) Tropical forest ecosystems in Africa and South America: a comparative review. Wash (page 183, Physocrema as junior synonym of Crematogaster [provisional])
- Emery, C. 1922c. Hymenoptera. Fam. Formicidae. Subfam. Myrmicinae. [part]. Genera Insectorum 174B: 95-206 (page 139, Physocrema as subgenus of Crematogaster)
- Forel, A. 1912g. Formicides néotropiques. Part III. 3me sous-famille Myrmicinae (suite). Genres Cremastogaster et Pheidole. Mém. Soc. Entomol. Belg. 19: 211-237 (page 220, Physocrema as subgenus of Crematogaster)
- Forel, A. 1917. Cadre synoptique actuel de la faune universelle des fourmis. Bull. Soc. Vaudoise Sci. Nat. 51: 229-253 (page 242, Physocrema as subgenus of Crematogaster)
- Hölldobler, B.; Wilson, E. O. 1990. The ants. Cambridge, Mass.: Harvard University Press, xii + 732 pp. (page 13, Physocrema as junior synonym of Crematogaster)
- Hosoishi, S. & Ogata, K. 2009b. A taxonomic revision of the Asian endemic subgenus Physocrema of the genus Crematogaster. Zootaxa 2062: 15-36. PDF
- Smith, D. R. 1979. Superfamily Formicoidea. Pp. 1323-1467 in: Krombein, K. V., Hurd, P. D., Smith, D. R., Burks, B. D. (eds.) Catalog of Hymenoptera in America north of Mexico. Volume 2. Apocrita (Aculeata). Washington, D.C.: Smithsonian Institution Pr (page 1376, Physocrema as junior synonym of Crematogaster)
- Soulié, J. 1964. Sur la répartition géographique des genres de la tribu des Cremastogastrini. Bull. Soc. Hist. Nat. Toulouse 99: 397-409 (page 398, Physocrema as genus)
- Wheeler, W. M. 1913a. Corrections and additions to "List of type species of the genera and subgenera of Formicidae". Ann. N. Y. Acad. Sci. 23: 77-83 (page 82, Type-species: Crematogaster inflata, by subsequent designation)
- Wheeler, W. M. 1922i. Ants of the American Museum Congo expedition. A contribution to the myrmecology of Africa. VII. Keys to the genera and subgenera of ants. Bull. Am. Mus. Nat. Hist. 45: 631-710 (page 662, Physocrema as subgenus of Crematogaster)