A new species of the rarely collected ant genus Platythyrea Roger, 1863 closely related to Platythyrea clypeata Forel, 1911 is described and illustrated based on the worker caste under the name Platythyrea janyaisp. n. This species is distributed in southern Thailand and western Malaysia, while P. clypeata is distributed in Sri Lanka, Vietnam, Laos, and Thailand in the areas north of the Isthmus of Kra. Platythyrea clypeata is newly recorded from Thailand from dead wood on the forest floor. The type series of P. janyai was also collected from rotten wood on the forest floor.
The Polyrhachis (Myrmatopa) flavicornis species group in Thailand is reviewed. Four species are recognized, of which one species closely related to Polyrhachis constructor Smith, 1857 is described and illustrated as new to science based on the worker caste under the name Polyrhachis longipilosa sp. nov. The queens of P. flavicornis Smith, 1857 and P. constructor, and the males of P. flavicornis and P. varicolor Viehmeyer, 1916 are described. The new species is distributed in western Thailand in the area north of the Isthmus of Kra, while P. constructor is distributed in Malaysia (West Malaysia and Sabah), Indonesia, Singapore, southern and western Thailand. Polyrhachis piliventris Smith, 1857 and Polyrhachis elii Emery, 1900 are synonymized with P. constructor. A key to the Thai species of the Polyrhachis flavicornis species group is given. The type series of P. longipilosa was collected from the canopy of a dry evergreen forest.
A taxonomic description of all castes of Colobopsis explodens Laciny & Zettel, sp. n. from Borneo, Thailand, and Malaysia is provided, which serves as a model species for biological studies on "exploding ants" in Southeast Asia. The new species is a member of the Colobopsis cylindrica (COCY) group and falls into a species complex that has been repeatedly summarized under the name Colobopsis saundersi (Emery, 1889) (formerly Camponotus saundersi). The COCY species group is known under its vernacular name "exploding ants" for a unique behaviour: during territorial combat, workers of some species sacrifice themselves by rupturing their gaster and releasing sticky and irritant contents of their hypertrophied mandibular gland reservoirs to kill or repel rivals. This study includes first illustrations and morphometric characterizations of males of the COCY group: Colobopsis explodens Laciny & Zettel, sp. n. and Colobopsis badia (Smith, 1857). Characters of male genitalia and external morphology are compared with other selected taxa of Camponotini. Preliminary notes on the biology of C. explodens Laciny & Zettel, sp. n. are provided. To fix the species identity of the closely related C. badia, a lectotype from Singapore is designated. The following taxonomic changes within the C. saundersi complex are proposed: Colobopsis solenobia (Menozzi, 1926), syn. n. and Colobopsis trieterica (Menozzi, 1926), syn. n. are synonymized with Colobopsis corallina Roger, 1863, a common endemic species of the Philippines. Colobopsis saginata Stitz, 1925, stat. n., hitherto a subspecies of C. badia, is raised to species level.