Aenictus inflatus

Remarkable for the genus in having a polymorphic worker caste, and an inflated propodeum (found filled with red liquid in the type colony) in larger workers. The smaller workers possess narrower heads with the sides almost parallel, very short antennae and legs, and normal propodea.

Identification
The only member of the inflatus species group.

Key to Aenictus species groups

Distribution based on Regional Taxon Lists
Indo-Australian Region: Borneo, Indonesia, Malaysia.

Biology
Yamane and Hashimoto reported the following about the colony from which the types were collected: In March 1997 during a night walk in the jungle we found a raiding column of a strange yellowish army ant in the Lambir Hills National Park, Sarawak, Borneo. Surprisingly the workers had distinctly inflated propodea that were filled up with a red liquid. When we collected workers from the column running down from the canopy very small workers, though few in number, were witnessed. A close examination of these small individuals under a binocular microscope revealed that they are clearly distinguished from the majority of workers by the lack of propodeal inflation and possession of very short antennae and legs. Since intermediate specimens were also found, this species may not be typically dimorphic. But it must be the first polymorphic Aenictus species with the peculiar propodeal inflation in larger specimens.

Allometric growth pattern in some body parts (see description) shows that this species is polymorphic (and almost dimorphic) in its worker caste. The small workers are more similar to usual workers of Aenictus species than are larger ones. They are easily distinguished from small species such as Aenictus piercei, Aenictus minutulus etc. by the long head with parallel sides and weak body sculpture (only mesothorax distinctly sculptured). Their function is not known. However, since they are few in number (ca. 3.3% of all the workers captured), there is a possibility that they are a mere expression of ancestral form of this species owing to the short supply of food during their larval stage. This situation is quite different from that described by Topoff (1971) for Aenictus laeviceps in which the smaller workers predominate in number.

Castes
Known only from the worker caste. Aenictus inflatus is unusual within the genus as it has a distinctly polymorphic worker caste. The majority of Aenictus  species are monomorphic, with a few exhibiting some weak polymorphism.

Nomenclature

 *  inflatus. Aenictus inflatus Yamane & Hashimoto, 1999: 428, fig. 1 (w.) BORNEO.

References based on Global Ant Biodiversity Informatics

 * Borowiec M. L. 2016. Generic revision of the ant subfamily Dorylinae (Hymenoptera, Formicidae). ZooKeys 608: 1–280.
 * Matsumoto T., T. Itioka, S. Yamane, and K. Momose. 2009. Traditional land use associated with swidden agriculture chnages encounter rates of the top predator, the army ant, in Southern Asian tropical rain forests. Biodivers. Conserv. 18: 3139-3151.
 * 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
 * Yamane S.; and Y. Hashimoto. 1999. A remarkable new species of the army ant genus Aenictus (Hymenoptera, Formicidae) with a polymorphic worker caste. Tropics 8: 427-432