Arnoldius

Arnoldius occurs in a wide variety of habitats, including grasslands, savanna woodlands, mallee forests, and lowland rain forests. Nests occur in soil with or without covering, in old termite nests, or in rotten wood. Workers are commonly found foraging on trees. Some species are known to establish new nests by invading established nests of Tapinoma and Iridomyrmex, that is, they are temporary social parasites. During nest founding, an Arnoldius queen will enter the nest of another ant species and kill its queen. The Arnoldius queen will then lay eggs which are tended and raised by the host ants as if they were laid by their own queen. As a result, the nest will contain workers of both Arnoldius and its host for a time after it is invaded, but eventually the host workers will die and the nest will contain only Arnoldius workers. This nest will then grow and produce new queens and males, and the cycle will repeat with another nest being invaded by a new Arnoldius queen.



Worker of Arnoldius from New South Wales.

Identification
The palps are short, do not reach the underside of the head beyond the mouthparts, and have a formula of 2:2 (both the inner and outer palps with 2 segments). The compound eyes are small, with between 10 and about 40 facets (ommatidia) and with a maximum diameter which is less than the maximum diameter of the scape. The front margin of the clypeus above the mandibles with 2 to about 12 downwardly curved hairs which are about the same length as or slightly shorter than the closed mandibles.

Workers of Arnoldius are similar in overall size and body shape to those of Acropyga, Doleromyrma, Plagiolepis, Tapinoma and Technomyrmex. They may be separated from Acropyga and Plagiolepis by their lack of an acidopore at the tip of the gaster, and from the remaining genera by their smaller compound eyes and short palps.

Extended Diagnosis Worker: Palp formula 4:3 or 2:2; compound eyes with between 10 and about 40 ommitidia; mandibles with 5-6 teeth, 0-5 denticles, a distinct basal angle, and a smooth basal margin; frontal carinae reduced or absent; anterior clypeal margin with 2 to 12 downward curved hairs which are about the same length as the closed mandibles; medial hypostoma absent. Europe and northern Africa east through India to Taiwan, and south to Australia.

Queen: Palp formula 4:3 or 2:2; medial hypostoma absent; anterior clypeal margin with 2 to 6 moderately curved setae; apical tooth of mandible elongate and much longer than subapical; dorsal face of propodeum shorter than declivitous face.

Male: Medial hypostoma absent; palp formula 4:3 or 2:2; pygostyles vestigial.

Distribution and Habitats
Australian distribution

Regional Species Lists

 * Australia

Keys to Species

 * Australia