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.

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.

Worker
HEAD. Vertex weakly convex to weakly concave. Compound eyes present, approximately round (sometimes reduced to about 10 ommitidia, but always distinct); relatively anterior on head. Ocelli absent. Antennae 12 segmented. Scape relatively short, at most surpassing the vertex by less than one-half (often less than one-third) its length. Anterolateral clypeal margin even with the mediolateral region. Anteromedial clypeal margin entire, without a central notch or concavity of any type, or with a broad, shallow concavity. Anterior clypeal setae 2-12; about the same length as the closed mandibles; moderately curved ventrally. Posterior clypeal margin even with or anterior to the anterior surfaces of the antennal socket cavities. Anterior tentorial pit nearer the antennal socket than the mandibular insertion. Frontal carina reduced or absent. Anterolateral hypostoma reduced to a thin sclerite. Medial hypostoma absent. Psammophore absent. MOUTHPARTS. Palp formula 4:3 or 2:2. Third maxillary palp segment (when present) subequal in length to segment 4. Mandible with 5-6 teeth and 0-5 denticles. Apical tooth slightly longer than the subapical tooth. Basal angle distinct, with a well developed tooth or angle separating the masticatory and basal margins. Basal margin smooth and without teeth or denticles. MESOSOMA. Posteroventral pronotum lateral, rounded or angled. Mesopleural process absent. Anteromedial mesosternum even with the lateral regions. Declivitous face of propodeum flat; dorsal face convex (sometimes weakly), shorter than the declivitous face. Propodeal angle indistinct to moderately distinct. Mesosomal spines and tooth absent. Erect pronotal hairs absent. Dorsal pro-mesonotal junction with the pronotum and mesonotum even, or with the mesonotum below the pronotum. Metanotal groove either reduced to a suture and with the mesonotum and propodeum forming a continuous, uninterrupted surface, or forming a distinct angle between the mesonotum and propodeum. Metanotal spiracle lateral and ventral of the dorsal surface when viewed in lateral profile. Propodeal spiracle lateral and ventral of the propodeal dorsum. Hind tibial spur with well developed barbules along entire inner surface (except extreme base). PETIOLE. Scale present; ridged and with a distinct angle dorsally; varying from moderately inclined anteriorly (but with the anterior and posterior faces approximately the same length) to strongly inclined anteriorly (and with the anterior face much shorter than the posterior face). Venter with a well developed lobe. GASTER. First tergite projecting anteriorly and concealing the petiole in dorsal view and with a groove or indentation for the reception of the entire height of the petiole. Anterior tergosternal suture of the first segment extending laterally from the helcium, either without a dorsal arch or with a distinct dorsal arch which is approximately the same height as the helcial dorsum. Fifth tergite ventral, gaster with 4 apparent tergites. Gastral compression weakly dorsoventral. Fourth sternite flat across entire posterior border. GENERAL CHARACTERS. Worker caste monomorphic. Chromosome number 11 (n=11, B. sp., Hauschteck 1963; B. gibbus, Crozier 1975). Integument thin and flexible, weakly sculptured. PROVENTRICULUS. Not examined.

Queen
HEAD. Vertex flat. Compound eyes relatively anterior on head. Antennae 12 segmented. Scape short, surpassing the vertex by less than one-half scape length. Anterolateral clypeal margin even with the mediolateral region. Anteromedial clypeal margin entire, without a central notch or concavity of any type, or with a broad, shallow concavity. Anterior clypeal setae 2-6; short, less than twice the maximum scape diameter to about the same length as the closed mandibles; moderately curved ventrally. Posterior clypeal margin between the anterior and posterior surfaces of the antennal socket cavities. Anterior tentorial pit nearer the antennal socket than the mandibular insertion. Anterolateral hypostoma reduced to a thin sclerite. Medial hypostoma absent. Psammophore absent. MOUTHPARTS. Palp formula 4:3 or 2:2. Mandible with 1-5 teeth (if 1 tooth, it is apical and the remainder of the masticatory border is smooth) and 0-4 denticles. Apical tooth elongate and much longer than the subapical tooth. Basal angle distinct, with a well developed tooth or angle separating the masticatory and basal margins. Basal margin smooth and without teeth or denticles. MESOSOMA. Posteroventral pronotum lateral, rounded or angled. Episternal suture complete. Mesopleural process absent. Anteromedial mesosternum even with the lateral regions. Axilla constricted medially. or absent dorsally (when present, entire). Declivitous and dorsal faces of propodeum convex to flat; dorsal face shorter than the declivitous face. Propodeal angle distinct. Propodeal suture absent. Mesosomal spines and tooth absent. Erect mesoscutal hairs absent. Propodeal spiracle lateral and ventral of the propodeal dorsum. Hind tibial spur with well developed barbules along entire inner surface (except extreme base). WINGS. Radial cell closed or open. Fore wing with 1 cubital and 0-1 discoidal cells. Hind wing with 1-2 cells. PETIOLE. Scale present; ridged and with a distinct angle dorsally; varying from moderately inclined anteriorly (but with the anterior and posterior faces approximately the same length) to strongly inclined anteriorly (and with the anterior face much shorter than the posterior face). Venter with a well developed, rounded lobe. GASTER. First segment projecting anteriorly and concealing the petiole in dorsal view and with a groove or indentation for the reception of the entire height of the petiole. Fifth tergite vertical and with the distal terminus of the gaster not well defined. Gastral compression absent (gaster circular in cross section). Fourth sternite flat across entire posterior border.

Male
HEAD. Inner margin of eye entire, flat. Scape length much longer than the length of funicular segments 1+2+3 but not exceeding the vertex. First funicular segment cylindrical or cone-shaped. Second funicular segment cylindrical, straight. Funicular segments 2 and 3 at most twice as long as broad. Third and fourth funicular segments straight. Anteromedial clypeal margin entire, without a central notch or concavity of any type. Anterior clypeal setae 4-10; short, about as long as the maximum diameter of the scape; straight. Posterior clypeal margin between the anterior and posterior surfaces of the antennal socket cavities. Anterior tentorial pit nearer the antennal socket than the mandibular insertion. Anterolateral hypostoma reduced to a thin sclerite. Medial hypostoma absent. MOUTHPARTS. Palp formula 4:2 or 2:2. Mandible with 2-3 teeth and no denticles (rarely with 3 teeth and a very small denticle). Apical tooth varying from slightly longer than, to elongate and much longer than, the subapical tooth. Basal angle indistinct, with a relatively uninterrupted curve between the two margins and without a distinct tooth or angle. Basal margin smooth and without teeth or denticles. MESOSOMA. Posteroventral pronotum lateral, rounded or angled. Episternal suture present, complete. Anteromedial mesosternum even with the lateral regions. Axilla constricted medially or absent dorsally. Anterior axillar suture straight. Declivitous face of propodeum convex; dorsal face convex, subequal in length to the declivitous face. Propodeal angle distinct. WINGS. Radial cell closed or open. Fore wing with 1 cubital and 0-1 discoidal cells. Pterostigmal appendage absent. Hind wing with 1-2 cells. PETIOLE. Scale present; ridged and with a distinct angle dorsally; vertical and not inclined anteriorly. Venter with a well developed lobe. Attachment to gaster fairly broad, but with a distinct posterior petiolar face. GASTER. First segment vertical and not concealing the petiole in dorsal view and with a groove or indentation for the reception of the entire height of the petiole. GENITALIA. Pygostyles vestigial. Posterior margin of subgenital plate convex. Paramere entire. Digitus with a down-turned tip. Cuspis absent. Ventral lobe of volsella absent. Aedeagus without ventral teeth.

Larva
Shape dolichoderoid. Protuberances present as 2 bosses located ventrolaterally on prothorax. Body hairs sparse; simple; short. 8 spiracular pairs. Antennae short.

Nomenclature

 *  ARNOLDIUS [Dolichoderinae: Bothriomyrmecini]
 * Arnoldius Dubovikov, 2005a: 93. Type-species: Bothriomyrmex flavus, by original designation.