Aenictus species groups

Jaitrong and Hashimoto (2011. Synopsis of Aenictus species groups and revision of the A. currax and A. laeviceps groups in the eastern Oriental, Indo-Australian, and Australasian regions (Hymenoptera: Formicidae: Aenictinae). Zootaxa, 3128, 1–46 ...and... 2012. Revision of the Aenictus minutulus species group (Hymenoptera Formicidae Aenictinae) from Southeast Asia. Zootaxa 3426, 29-44.). These groupings are based on similarities in worker morphology (Key to Aenictus species groups).

Aenictus ceylonicus group

 * Aenictus acerbus
 * Aenictus ceylonicus
 * Aenictus doryloides
 * Aenictus exilis
 * Aenictus fuchuanensis
 * Aenictus henanensis
 * Aenictus nganduensis
 * Aenictus orientalis
 * Aenictus schneirlai
 * Aenictus thailandianus
 * Aenictus turneri

Diagnosis. Antenna 10-segmented; scape reaching or extending beyond half of head length, but not reaching the occipital corner of head in full-face view. Mandible linear; its basal and lateral margins almost parallel; masticatory margin with large apical tooth followed by medium-sized subapical tooth; between subapical tooth and basal tooth 0–6 small denticles present. With mandibles closed, a gap present between mandibles and anterior margin of clypeus. Anterior clypeal margin weakly concave or almost straight, lacking denticles. Frontal carina short and thin, reaching or slightly extending beyond the level of posterior margin of torulus; anterior curved extension of frontal carina reaching or extending beyond the level of anterior clypeal margin in full-face view; parafrontal ridge absent. Promesonotum usually convex dorsally and sloping gradually to propodeum. Subpetiolar process developed.

Head and first gastral tergite smooth and shiny. Body yellowish, reddish or dark brown; typhlatta spot absent.

Distribution. India, Sri Lanka, southernmost part of Japan (?), S. China, Taiwan, Vietnam, Thailand, Borneo (Sabah and Sarawak), Philippines, Aru Island (Indonesia), New Guinea (Papua), and Australia (Queensland).

Remarks. The A. ceylonicus group is a unique group easily separated from the other groups by the following characteristics: mandible linear; a gap present between mandibles and anterior margin of clypeus when mandibles are closed; anterior clypeal margin almost straight or feebly concave, lacking denticles. Our concept roughly agrees with Wilson’s (1964) definition of the “ceylonicus group”, but three species, A. biroi, A. javanus and A. piercei, should be removed from his list since they have triangular mandibles and different conditions of the anterior clypeal margin. All these species belong to three different species groups.

Aenictus currax group

 * Aenictus cornutus
 * Aenictus currax
 * Aenictus diclops
 * Aenictus glabrinotum
 * Aenictus gracilis
 * Aenictus huonicus
 * Aenictus pfeifferi
 * Aenictus parahuonicus
 * Aenictus wayani

Diagnosis. Head in full-face view with occipital corner convex and with a distinct protuberance, which gives the head a unique “horned” appearance; occipital margin forming a carina. Antenna 10-segmented. Anterior clypeal margin roundly convex, lacking denticles. Mandible subtriangular; its masticatory margin with a large apical tooth followed by a medium-sized subapical tooth, and 4–6 denticles. Frontal carina short, extending a little beyond posterior margin of torulus; parafrontal ridge feeble and incomplete or almost absent. With mesosoma in profile promesonotum convex dorsally and sloping gradually to metanotal groove. Legs slender. Subpetiolar process present; its anteroventral corner always angular, and directed forward and downward.

Head and first gastral segment entirely smooth and shiny. Body black, dark brown to reddish brown; typhlatta spot present, always located at the occipital corner of head.

Distribution. Vietnam, Laos, Myanmar, Thailand, Malay Peninsula (S. Thailand and W. Malaysia), Sumatra Indonesia, Borneo (Sabah, Sarawak, Brunei, and E. Kalimantan), Sulawesi, New Guinea, and Australia.

Remarks. Our concept agrees well with Wilson’s (1964) definition of the “currax group”. This species group is closely related to the A. leptotyphlatta group and A. laeviceps group, all bearing typhlatta spots on the worker head, and also sharing the black or dark brown to reddish brown body, and entirely smooth and shiny head (Jaitrong & Eguchi 2010). The A. currax group is distinguished from the latter two by the following characteristics:anterior clypeal margin roundly convex, lacking denticles; head in full-face view with occipital corner convex and with a distinct protuberance, which gives the head a unique “horned” appearance; in profile “typhlatta spot” always located at occipital corner; subpetiolar process present, triangular with the apex always directed forward and downward.

Aenictus hottai group

 * Aenictus hottai
 * Aenictus yamanei

Diagnosis. Antenna long, consisting of 10 segments; scape long, reaching posterolateral corner of head. Anterior clypeal margin roundly convex, lacking denticles. Mandible subtriangular, with very dense punctures; its masticatory margin with a large and sharp apical tooth followed by a medium-sized subapical tooth and 18–20 small inconspicuous denticles. Frontal carina not reaching midlength of head, well developed anteriorly and poorly developed posteriorly; parafrontal ridge present not reaching midlength of head; seen in profile its anteriormost part well developed and raised as a subtriangular process, and poorly developed posteriorly. Occipital margin of head forming a collar or carina. Propodeal junction angular; declivity of propodeum concave, encircled with a rim. Subpetiolar process well developed, posteroventrally produced. Entire head, mesosoma, petiole and postpetiole very densely puncto-recticulate and opaque. Punctoreticulation on antennal scape, coxae, femora, tibiae, and basitarsi similarly dense but weaker. First gastral segment with dense but weak and superficial micropunctation, subopaque and slightly shiny. Body dark brown to reddish brown; typhlatta spot absent.

Distribution. Malay Peninsula (S. Thailand and W. Malaysia), W. Sumatra (Indonesia), and Borneo (Sarawak).

Remarks. This species group is closely related to the A. pachycerus group and A. philippinensis group in that all have a well-developed frontal carina and parafrontal ridge. The A. hottai group can be separated from other groups by the first gastral segment being densely micropunctate, subopaque and slightly shiny, and by the well developed subpetiolar process which is posteroventrally produced (in the other groups the first gastral segment is smooth and shiny).

Aenictus inflatus group
Diagnosis. Largest worker. Head in full-face view with occipital corner rounded; occipital margin lacking collar. Antenna long, consisting of 10 segments; antennal scape widened in apical half, reaching posterolateral corner of head in full-face view. Anterior clypeal margin roundly convex, lacking denticles. Mandible triangular; its masticatory margin with a large apical tooth, medium-sized subapical and basal teeth, with 4–5 denticles between subapical and basal teeth. Frontal carina very short, not extending beyond posterior margin of torulus; parafrontal ridge absent. With mesosoma in profile promesonotum convex dorsally and sloping gradually to metanotal groove; propodeum broader than pronotum, distinctly inflated. Legs slender. Subpetiolar process weakly developed or almost absent.

Head and first gastral segment entirely smooth and shiny. Body yellow to yellowish brown; head darker than other parts; typhlatta spot present, located at occipital corner. Variation. The single species of this group, A. inflatus Yamane et Hashimoto, 1999, is clearly polymorphic in the worker caste. Several very small workers were found among the type series and workers of other colonies. They are characterized by a relatively long head, short antennal scape reaching only midlength of head, and normal propodeum. The typhlatta spot is less pronounced in these specimens. Between the largest and smallest workers we have found a series of specimens that are intermediate in the development of propodeum and length of antenna and legs (see also Yamane & Hashimoto 1999).

Remarks. Yamane and Hashimoto (1999) erroneously mentioned that the antenna is 12-segmented when it was in fact 10-segmented. The smallest worker of this group is most similar to the worker of the A. wroughtonii group in having a yellowish and slender body, long legs and weakly developed subpetiolar process. But in the former, the anterior clypeal margin is convex, lacking denticles and the antennal scape reaches only the midlength of the head, while in the latter, the anterior clypeal margin is roundly convex with 5–10 denticles and the antennal scape attains or extends beyond posterolateral corner of the head. The inflated propodeum of A. inflatus contains a red liquid in living specimens; this liquid dissolves in alcohol.

Aenictus minutulus group
(Aenictus piercei group in Jaitrong et Yamane, 2011)


 * Aenictus changmaianus
 * Aenictus minimus
 * Aenictus minutulus
 * Aenictus peguensis
 * Aenictus subterraneus

Diagnosis. In an earlier paper (Jaitrong & Yamane 2011) this species group was defined as follows: head in fullface view with occipital corner convex, and posterior margin almost straight to shallowly and broadly concave; occipital margin lacking collar; antenna 10-segmented; antennal scape short reaching only midlength of head; anterior clypeal margin roundly convex, lacking denticles; mandible subtriangular; its masticatory margin with a large apical tooth, medium-sized subapical and basal teeth, and 2-6 denticles between them; basal margin of mandible with conspicuous denticles; frontal carina short; parafrontal ridge absent; with mesosoma in profile promesonotum convex dorsally and sloping gradually to propodeum; metapleural groove present or absent (mesonotum and propodeum fused); propodeal junction angulated; subpetiolar process well developed, triangular or subrectangular. Head and first gastral segment entirely smooth and shiny. Body yellowish brown to reddish brown; typhlatta spot absent.

Size variation occurs among individuals from single colonies.

'''Distribution. '''Southernmost part of Japan, Taiwan, Myanmar, Thailand, Sumatra (Indonesia), and Philippines.

Remarks. This is a group of rather small species, measuring 1.80-3.20 mm in total body length. It is most similar to the Aenictus javanus group in terms of body size and coloration, but in the former the anterior clypeal margin lacks denticles, while it has several denticles in the latter.

The Aenictus piercei group was established by Jaitrong and Yamane (2011) to include five named species occurring in Southeast Asia: Aenictus changmaianus, Aenictus lifuiae, Aenictus minutulus, Aenictus peguensis and Aenictus  piercei. However, after carefully examining the type material and an associated specimen of A. piercei we concluded that this species should be removed from this group and that it is a member of the A. javanus group (A. piercei has denticles on the anterior margin of clypeus). The A. piercei group is renamed here as the A. minutulus group.

After a careful examination of the smaller specimens of A. lifuiae collected from Iriomote-jima and Okinawajima, southern Japan, we found that the mandible is almost linear, the anterior clypeal margin is straight or weakly concave, and that a gap occurs between the mandibles and anterior clypeal margin. These characteristics are used to separate the A. ceylonicus group from the other groups of the genus Aenictus, and also these specimens possess other conditions shared with the A. ceylonicus group. We transfer A. lifuiae to the A. ceylonicus group.