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
Aenictus inflatus

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, Aenictus 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).

Distribution. Borneo (Sarawak).

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 Aenictus inflatus contains a red liquid in living specimens; this liquid dissolves in alcohol.

Aenictus javanus group

 * Aenictus doydeei
 * Aenictus javanus
 * Aenictus nishimurai

Diagnosis. Head in full-face view with occipital corner convex; occipital margin lacking collar. Antenna 10-segmented; antennal scape short extending only half length of head. Anterior clypeal margin roundly convex bearing 6–10 denticles. Mandible subtriangular; masticatory margin with 3 teeth including the large apical tooth. Frontal carina short, not extending beyond the level of posterior margin of torulus. Parafrontal ridge absent. Mesosoma in profile with dorsal margin almost flat; dorsal face of mesosoma meeting with lateral face at a right angle; propodeal junction angular; propodeal declivity encircled with a thin rim. Subpetiolar process developed, triangular or subrectangular.

Head and first gastral segment entirely smooth and shiny except the base of gastral tergite I and sternite I that have dense small punctures. Body reddish brown to yellowish brown; typhlatta spot absent.

Distribution. Vietnam, Laos, Thailand, and W. Java (Indonesia).

Remarks. This is a group of relatively small ants measuring 1.38–3.40 mm in total length. It is similar to the A. piercei group in terms of body size and coloration, but in the former the anterior clypeal margin has several denticles, while it lacks denticles in the latter. Though Wilson (1964) treated Aenictus javanus as a member of the A. ceylonicus group, it has a quite different set of characteristics as mentioned above.

Aenictus laeviceps group

 * Aenictus alticola
 * Aenictus binghami
 * Aenictus bodongjaya
 * Aenictus breviceps
 * Aenictus brevinodus
 * Aenictus fergusoni
 * Aenictus fulvus
 * Aenictus hodgsoni
 * Aenictus laeviceps
 * Aenictus luzoni
 * Aenictus montivagus
 * Aenictus rotundicollis
 * Aenictus siamensis
 * Aenictus sonchaengi

Diagnosis. Head in full-face view with occipital corner rounded; occipital margin forming a carina. Antenna 10-segmented; antennal scape relatively long, usually attaining posterior corner of head. Anterior clypeal margin roundly convex, bearing 5–12 denticles. Mandible subtriangular; its masticatory margin with a large apical tooth followed by a medium-sized subapical tooth and 5–8 denticles. Frontal carina short, extending slightly 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 well developed, triangular; its apex usually directed backward and downward. Head and first gastral segment entirely smooth and shiny. Body black, dark brown to reddish brown; typhlatta spot present, usually located anterior to occipital corner.

Distribution. India, Vietnam, Cambodia, Thailand, Malay Peninsula (S. Thailand and W. Malaysia), Sumatra (Indonesia), Borneo (Sabah, Sarawak, Brunei, and E. Kalimantan), Java (Indonesia), Philippines, and Sulawesi (Indonesia).

Remarks. Our concept agrees well with Wilson’s (1964) definition of the laeviceps group. This group is closely related to the A. currax group and A. leptotyphlatta group (see under A. currax group). The A. laeviceps group is distinguished from the latter two by the following characteristics: anterior clypeal margin roundly convex with several denticles; head in full-face view with occipital corner rounded; in profile typhlatta spot usually located anterior to occipital corner; subpetiolar process well developed, with the apex directed downward and backward.

Aenictus leptotyphlatta group
Aenictus leptotyphlatta

Diagnosis. Head in full-face view with occipital corner rounded; occipital margin lacking collar. Antenna 10-segmented; antennal scape short, reaching or extending slightly beyond midlength of head. Anterior margin of clypeus slightly convex medially, lacking denticles. Mandible subtriangular; its masticatory margin with a large apical tooth followed by 4–5 relatively large teeth. Frontal carina short and thin, extending posteriad, not beyond the level of posterior margin of torulus; anterior curved extension of frontal carina reaching or extending beyond the level of anterior clypeal margin. With mesosoma in profile promesonotum weakly convex dorsally and sloping gradually to propodeum. Legs slender. Subpetiolar process well developed, triangular, with its apex directed downward. Head and first gastral segment entirely smooth and shiny. Body black to dark brown; typhlatta spot present but not clear.

Distribution. Thailand.

Remarks. This group is closely related to the A. currax group and A. laeviceps group (see under A. curraxgroup). The A. leptotyphlatta group exhibits conditions intermediate between the A. currax group and A. laeviceps group. It has the anterior clypeal margin lacking denticles as in the A. currax group, but the occipital corner of the head is similar to that of the A. laeviceps group. Furthermore the typhlatta spot is less clearly demarcated from the background, and much paler in coloration than in the other typhlatta-bearing species groups.

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.

Aenictus pachycerus group

 * Aenictus aitkenii
 * Aenictus aratus
 * Aenictus bobaiensis
 * Aenictus carolianus
 * Aenictus chapmani
 * Aenictus dentatus
 * Aenictus levior
 * Aenictus nesiotis
 * Aenictus pachycerus
 * Aenictus philiporum
 * Aenictus powersi
 * Aenictus prolixus
 * Aenictus punensis
 * Aenictus reyesi

Diagnosis. Antenna long, consisting of 10 segments; scape long, reaching or extending beyond posterolateral corner of head. Anterior clypeal margin roundly convex in the middle, lacking denticles. Mandible triangular, with very dense punctures; its masticatory margin with a large and sharp apical tooth followed by 4–12 small inconspicuous denticles, which gradually reduce in size toward basal angle of mandible. Frontal carinae fused at the level of antennal base to form a single carina, and extending less than half length of head, and well developed anteriorly and poorly developed posteriorly; parafrontal ridge present, reaching less than half length of head; seen in profile its anteriormost part well developed and raised as a subtriangular process. Occipital margin forming a collar or carina. Promesonotum distinctly convex or very weakly convex dorsally and sloping gradually to propodeum; propodeal junction angular; declivity of propodeum concave, encircled with a rim. Subpetiolar process weakly developed.

Head entirely sculptured or smooth and shiny. Petiole and postpetiole densely punctate in at least Southeast Asian species. First gastral segment entirely smooth and shiny, or rarely superficially shagreened, except the base of the tergite and sternite that has small, dense punctures. Body black, dark or reddish brown to light or yellowish brown; typhlatta spot absent.

Distribution. India, Sri Lanka, S. China, Vietnam, Thailand, Malay Peninsula (S. Thailand and W. Malaysia), Sumatra (Indonesia), Borneo (Sabah, Sarawak, Brunei, and E. Kalimantan), Philippines, New Guinea (Papua), and Australia (Queensland).

Remarks. The A. pachycerus group consists of relatively large species in terms of body size (TL 3.20–4.65 mm). Wilson (1964) pointed out that this group is closely related to the A. philippinensis group, but can be distinguished from the latter by the mesonotum not visibly demarcated from the mesopleuron, and the metanotal groove almost absent or indistinct (mesopleuron clearly demarcated from metapleuron by a deep groove and from promesonotum by a distinct carina and metanotal groove relatively deep and distinct in the latter). This species group is also related to the A. hottai group in having developed frontal carina and parafrontal ridge. See under the A. hottai group.

Aenictus philippinensis group

 * Aenictus pangantihoni
 * Aenictus philippinensis
 * Aenictus rabori

Diagnosis. Antenna 10-segmented; scape not reaching the posterolateral corner of head. Anterior clypeal margin convex in the middle, lacking denticles. Mandible triangular, with very dense punctures; its masticatory margin with a large and sharp apical tooth followed by 6–8 small inconspicuous denticles. Frontal carinae fused at the level of antennal base to form a single carina, extending less than half length of head, and well developed anteriorly and poorly developed posteriorly; parafrontal ridge present, not reaching midlength of head. Occipital margin forming a collar or carina. Mesosoma in profile with promesonotum convex dorsally and sloping gradually to metanotal groove; mesopleuron clearly demarcated from metapleuron by a deep groove and from promesonotum by a distinct carina; metanotal groove relatively deep and distinct; propodeal junction angular; declivity of propodeum concave, encircled with a rim. Subpetiolar process weakly developed.

First gastral segment entirely smooth and shiny except the base of both tergite and sternite which has dense small punctures. Body reddish brown to dark brown; typhlatta spot absent.

Distribution. Philippines.

Remarks. This group consists of relatively large species measuring 4.05–4.60 mm in total body length, and is closely related to the A. pachycerus group and A. hottai group. However, the A. philippinensis group is separated from these by having the mesonotum demarcated from the mesopleuron by a conspicuous ridge and the metanotal groove being relatively deep and distinct. The sculpture of the head is variable, from entirely smooth to densely puncto-reticulate.