Dolichoderus

This is a large, diverse genus which occurs in forested areas, from dry savanna woodlands to rain forests. Some species form small, cryptic colonies in soil, hollow plant stems, and litter. Others have large colonies that make small mounds of vegetative debris and forage along conspicuous trails, frequently in bogs or pine barrens. Still others form large arboreal nests sometimes using plant fibers to form coverings during nest construction. In general, workers are diurnal and are general scavengers and also tend aphids and other Hemiptera. They often forage in columns on the ground or on low vegetation and trees. During warm weather, some species will move their larvae to the surface of the ground for warmth.

This genus is also known from Oligocene fossils (35-25 million years before present).

Identification
The underside of the head near the base of the mandible (anterior hypostoma) with a weak to well developed flange that is sometimes tooth-like. Spines are sometimes present on the pronotum and propodeum, or just the propodeum. If spines are absent from the propodeum, then the rear face of the propodeum is often distinctly concave, but may be flat. The body is often strongly sculptured. The plates on the underside of the body above the front legs (visible only when the front legs are removed) expanded and overlapping along the centre-line of the body.

Extended diagnosis

Worker: Anterior hypostoma in the form of an expanded flange directed anteroventrally (sometimes only weakly so); mesopleural process generally present, sometimes reduced to a blunt protuberance or swelling, occasionally absent; spines sometimes present on thoracic dorsum; integument often strongly sculptured; mesosternum expanded anteriorly.

Queen: Anterior hypostoma in the form of an expanded flange directed anteroventrally (sometimes only weakly so); declivitous face of propodeum concave; mandible with 11 to 22 teeth and no denticles, and the apical tooth subequal in length to the subapical; venter of the petiole without a lobe.

Male: Inner margin of compound eye angular; anterior hypostoma in the form of an expanded flange directed anteroventrally; mandible with 25 to 27 teeth and no denticles, and with the basal margin denticulate along its entire surface; declivitous face of propodeum flat or concave.

Within Australia there are four sets of species. Two of these (subgenera Acanthoclinea and Diceratoclinea) have long spines on the pronotum and propodeum, or just the propodeum. These spines do not occur in any other genera of the Dolichoderinae except Froggattella. In another set, the rear face of the propodeum is weakly to strongly concave. This is similar to species of Ochetellus, but Dolichoderus differs in being larger (greater than 3mm in total length) and in having a small flange on the underside of the head as mentioned above. The metanotal groove in Dolichoderus is also deeper and broader, and, in many species, the body is more heavily and distinctly sculptured. The final group of Dolichoderus have the body essentially smooth and the rear face of the propodeum flat to weakly convex.

Dolichoderus species groups

Australia
Shattuck and Mardsen (2013) - All of the 27 described species of Australian Dolichoderus are endemic to Australia. The species can be divided into four species groups, with two of the four groups (the doriae and scabridus groups) endemic, one (the australis group) also occurring in New Caledonia (represented by the species Dolichoderus tricolor) while the final group, the scrobiculatus group, is part of the subgenus Hypoclinea which occurs throughout North and South America and Europe eastward into Southeast Asia. Within Australia 12 species are found in the south-east corner while 8 species are occur broadly across southern Australia. Four species are restricted to south-west Western Australia while another four are found only in Queensland. South Australia has three species which occur only there while a single species is widespread along the eastern Australian coast. The genus is unknown from northern Australia outside of Queensland. It is also worth noting that numerous species (for example Dolichoderus clarki, Dolichoderus etus and Dolichoderus rufotibialis) have restricted ranges, and even widespread species such as Dolichoderus clusor and Dolichoderus formosus consist of several narrowly distributed disjunct populations. In contrast, other species are quite broadly distributed, occurring across much of southern Australia (Dolichoderus omicron, Dolichoderus parvus and Dolichoderus reflexus) or along the east coast (Dolichoderus scrobiculatus).

A curious distribution pattern emerged while examining material from this group. While it is fairly common to find “outlier” specimens in most groups, specimens which occur significantly outside the main range of a species, these were unusually common in Dolichoderus. Normally outliers can be explained as specimen labelling errors or similar processing mistakes, but their presence across several species would seem to indicate that this may not be the case here. For example, outliers have been found in D. doriae, D. extensispinus, D. inferus, D. parvus, D. reflexus, D. scobiculatus and D. turneri. Unfortunately all of these have been “one-off” collections and none confirmed with multiple collections. Given that most of these are from relatively well collected areas it remains to be seen if these outliers are the result of labelling errors, short-lived dispersal events or low density established populations. In any event it is interesting that this phenomenon appears to be common in this group.

From an evolutionary perspective, it seems likely that the doriae and scabridus groups are derived from the “spiny” Dolichoderus of South America, specifically from an ancestor of modern-day species placed previously in the subgenus Monacis (currently considered to be a synonym of Dolichoderus). This dispersal pattern, from South America into Australia, is the same as observed for Iridomyrmex and close relatives (Ward et al., 2009). It would then appear that member(s) of the scabridus group dispersed north from Australia into New Guinea and Indonesia, giving rise to species of Monoceratoclinea and Dolichoderus indrapurensis (previously placed together with species of the scabridus group) which share the development of a decorated propodeum and lack pronotal spines (thus making the doriae group a less likely ancestor). The subgenus Karawajewella, with its single species Dolichoderus cuspidatus, would appear to have an independent evolutionary origin, possibly from a Dolichoderus erectilobus-like ancestor.

The origins of the australis and scrobiculatus groups are less clear. Both are part of the subgenus Hypoclinea which is found in North and South America and Europe east to Malaysia and Indonesia. Hypoclinea has not been recorded from New Guinea and appears to be absent from this island. Members of the australis group are unlike overseas Hypoclinea in having a relatively “thin”, unsculptured cuticle and a weakly concave posterior propodeal face. It seems probable that this group arose within the Australian region from a local ancestor and is endemic to this region. On the other hand, members of the scrobiculatus group are similar to “typical” Hypoclinea, supporting a relatively close relationship with other members of this subgenus. This leaves open the possibility of the Australian fauna being derived from either South America or Southeast Asia. Of these two, the most morphologically similar species occur in Southeast Asia with species such as Dolichoderus sibiricus and Dolichoderus thoracicus generally resembling Australian species. This would increase the likelihood

To summarise, it would appear that the Australian Dolichoderus fauna is derived from three sources: 1) the doriae and scabridus groups from South America through a Monacis-like ancestor, 2) the scrobiculatus group from Asia through a Hypoclinea ancestor and 3) the australis group arising within the Australian region, probably from a scrobiculatus-like ancestor. A member of the scabridus group then dispersed north into New Guinea and Southeast Asia, giving rise to several additional species (those placed in Monoceratoclinea as well as Dolichoderus indrapurensis). Further detailed study of the world DoliItalic textchoderus fauna will be necessary to confirm these hypotheses, especially studies using expanded dataset which include molecular data and undertake detailed biogeographic analyses.

Fossils
Fossils are known from:, , , , , , , , , , , , , , , , , , (an unidentified species, Wang et al., 2021).

Biology
Shattuck and Marsden (2013) - Dolichoderus is a large, diverse genus which occurs throughout the world with the exception of Saharan and sub-Saharan Africa. Within Australia species are found primarily in southern and eastern forested areas, from mallee and savannah woodlands to wet sclerophyll forests, with the genus absent from the north-west and with only a handful of species occurring in the arid habitats of central Australia and in rainforests along the east coast.

In general, workers are diurnal and are general scavengers as well as tending aphids and other Hemiptera for honeydew. They often forage in columns on the ground or on low vegetation and trees. Nests are in soil generally under rocks or in rotten wood. During warm weather, some species of the doriae group will move their larvae to the surface of the ground for warmth, forming distinctive “balls” of workers and larvae. While most species have normal, fully winged queens only worker-like ergatoid queens are known for species in the doriae and scabridus groups.

Description
WORKER

HEAD. Vertex convex to concave (occasionally drawn posteriorly into a neck). Compound eyes present, approximately round; position on head variable. 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 posterior to the mediolateral region and separated from it by a shoulder, or 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 4-28; short, less than twice the maximum scape diameter; straight. Posterior clypeal margin posterior of the anterior surfaces of the antennal socket cavities. Anterior tentorial pit nearer the antennal socket than the mandibular insertion. Frontal carina present. Anterolateral hypostoma in the form of an expanded flange directed anteroventrally. Medial hypostoma entire. Psammophore absent (rarely numerous elongate hairs on gula and ventral surface of mandibles). MOUTHPARTS. Palp formula 6:4. Third maxillary palp segment subequal in length to segment 4. Fifth maxillary palp segment at the apical extreme of segment 4. Mandible with about 11-13 teeth and no denticles. Apical tooth subequal in length to the subapical tooth. Basal angle indistinct, with a relatively uninterrupted curve between the two margins, or weakly defined by a denticle. Basal margin denticulate along entire surface. MESOSOMA. Posteroventral pronotum elongate and expanded medially. Mesopleural process present (in the form of a spine, blunt protuberance, or lateral swelling), or absent. Anteromedial mesosternum expanded anteriorly relative to the lateral regions. Declivitous face of propodeum concave (rarely flat, nearly convex, or convex); dorsal face convex (rarely with a single, dorsal spine), subequal in length to the declivitous face. Propodeal angle distinct (sometimes with a ridge or carina). Pronotal spines present and distinct, or absent (sometimes with angles laterally). Erect pronotal hairs 20-35 (occasionally absent); short, about as long as maximum scape width to elongate and much longer than the maximum scape width. Mesonotal spines present and distinct, reduced to protuberances, or absent. Propodeal spines present and distinct, or absent (in some, concave medially with lateral edges raised). Propodeal tooth absent. Dorsal pro-mesonotal junction variable, with the mesonotum above or below the pronotum. Metanotal groove forming a distinct angle between the mesonotum and propodeum, or a narrow, distinct notch in the relatively flat dorsal mesosomal surface. Metanotal spiracle lateral and ventral of the dorsal surface when viewed in lateral profile, or dorsal and lying on 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; rounded and forming an even arch dorsally, ridged and with a distinct angle dorsally, or spined and with a single or double tooth or projection dorsally; moderately inclined anteriorly but with the anterior and posterior faces approximately the same length. Venter without a lobe. GASTER. First tergite vertical and not concealing the petiole in dorsal view, smooth and without a groove or indentation or with a groove or indentation for the reception of the basal portion of the petiole. Anterior tergosternal suture of the first segment extending laterally from the helcium, without or with at most a very weak dorsal arch. Fifth tergite ventral, gaster with 4 apparent tergites (sometimes narrowed longitudinally). Gastral compression lateral or dorsoventral. Fourth sternite keel-shaped posteriorly. GENERAL CHARACTERS. Worker caste monomorphic. Chromosome number 14-16 (2n=28, D. quadripunctatus, Imai 1969; 2n=30, D. bituberculatus (=D. thoracicus), Imai et al. 1985b; 2n=30, 31, 32 and 33, D. bituberculatus (=D. thoracicus), Imai et al. 1985a; n=14, D. scabridus, Crozier 1970a; 2n=28, D. scabridus, Imai et al. 1977). Integument thickened, often strongly sculptured. PROVENTRICULUS. Cupola narrow relative to bulb; round; with short pile; smooth, without sculpture; and without phragma. Bulb exposed in lateral view. Longitudinal muscle No. 1 present. Occlusory tract absent.

QUEEN

HEAD. Vertex convex to weakly concave. Compound eyes relatively anterior on head. Antennae 12 segmented. Scape variable, short (surpassing the vertex by less than one-half scape length) or long (surpassing the vertex by more than one-half scape length). Anterolateral clypeal margin even with the mediolateral region, or with the corners expanded slightly anterior of the mediolateral region. Anteromedial clypeal margin entire, without a central notch or concavity of any type. Anterior clypeal setae 6-8; short, less than twice the maximum scape diameter; straight. Posterior clypeal margin posterior of the anterior surfaces of the antennal socket cavities. Anterior tentorial pit nearer the antennal socket than the mandibular insertion. Anterolateral hypostoma in the form of an expanded flange directed anteroventrally. Medial hypostoma entire. Psammophore absent. MOUTHPARTS. Palp formula 6:4. Third maxillary palp segment subequal in length to segment 4. Fifth maxillary palp segment at the apical extreme of segment 4. Mandible with 11-22 teeth and no denticles. Apical tooth subequal in length to the subapical tooth. Basal angle distinct, with a well developed tooth or angle separating the masticatory and basal margins. Basal margin denticulate along entire surface. MESOSOMA. Posteroventral pronotum elongate and expanded medially. Episternal suture complete. Mesopleural process present or absent. Anteromedial mesosternum expanded anteriorly relative to the lateral regions. Axilla parallel or constricted medially, and entire. Anterior axillar suture straight. Declivitous face of propodeum concave; dorsal face convex, subequal in length to the declivitous face. Propodeal angle distinct. Propodeal suture complete (obscured near the metapleural gland bulb) or absent. Pronotal spines present and distinct, or absent. Erect mesoscutal hairs 4-60; short, less than twice the maximum scape diameter to elongate, more than twice the maximum scape diameter. Propodeal spines present as protuberances, or absent. Propodeal tooth 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. Fore wing with 2 cubital and 1 discoidal cell. Hind wing with 2 cells. PETIOLE. Scale present; rounded and forming an even arch dorsally, ridged and with a distinct angle dorsally, or spined and with a single tooth or projection dorsally; vertical and not inclined anteriorly to strongly inclined anteriorly and with the anterior face much shorter than the posterior face. Venter without a lobe. GASTER. First segment vertical and not concealing the petiole in dorsal view, smooth and without a groove or indentation or with a groove or indentation for the reception of the entire height of the petiole. Fifth tergite ventral, gaster with 4 apparent tergites. Gastral compression absent (gaster circular in cross section). Fourth sternite flat across entire posterior border.

MALE

HEAD. Inner margin of eye angular. Scape length at most only slightly longer than the length of funicular segments 1+2+3. 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 about 5-7; short, about as long as the maximum diameter of the scape; straight. Posterior clypeal margin posterior to the anterior surfaces of the antennal socket cavities. Anterior tentorial pit nearer the antennal socket than the mandibular insertion. Anterolateral hypostoma in the form of an expanded flange directed anteroventrally. Medial hypostoma entire. MOUTHPARTS. Palp formula 6:4. Third maxillary palp segment subequal in length to segment 4. Fifth maxillary palp at the apical extreme of segment 4. Mandible with about 25-27 teeth and no denticles. 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 denticulate along entire surface. MESOSOMA. Posteroventral pronotum weakly expanded medially. Episternal suture present, complete. Anteromedial mesosternum even with the lateral regions, or weakly expanded anteriorly relative to the lateral regions. Axilla constricted medially and entire. Anterior axillar suture straight. Declivitous face of propodeum flat to concave; dorsal face convex, subequal in length to the declivitous face. Propodeal angle distinct. WINGS. Radial cell closed. Fore wing with 2 cubital and 1 discoidal cell. Pterostigmal appendage absent. Hind wing with 2 cells. PETIOLE. Scale present; rounded and forming an even arch dorsally, or ridged and with a distinct angle dorsally; vertical and not inclined anteriorly. Venter without a lobe. Attachment to gaster narrow. GASTER. First segment elongated posteriorly to vertical and not concealing the petiole in dorsal view, smooth and without a groove or indentation. GENITALIA. Pygostyles present. Posterior margin of subgenital plate concave or with a "V"-shaped notch. Paramere entire. Digitus with a down-turned tip. Cuspis parallel with digitus. Ventral lobe of volsella present as concave lobe. Aedeagus with ventral teeth.

LARVA

Shape dolichoderoid. Protuberances present or absent; when present, as 2 bosses located ventrolaterally on prothorax. Body hairs sparse; simple; short. 10 spiracular pairs.

Nomenclature

 *  DOLICHODERUS [Dolichoderinae: Dolichoderini]
 * Dolichoderus Lund, 1831a: 130. Type-species: Formica attelaboides, by monotypy.
 * Dolichoderus senior synonym of Hypoclinea, Monacis: Forel, 1878: 386; Dalla Torre, 1893: 156; Shattuck, 1992c: 66.
 * Dolichoderus senior synonym of Acanthoclinea, Diceratoclinea: Taylor & Brown, D.R. 1985: 93; Shattuck, 1992c: 66.
 * Dolichoderus senior synonym of Diabolus (junior homonym), Karawajewella, Monoceratoclinea: Shattuck, 1992c: 66.
 * ACANTHOCLINEA [junior synonym of Dolichoderus]
 * Acanthoclinea Wheeler, W.M. 1935c: 69 [as subgenus of Dolichoderus]. Type-species: Dolichoderus doriae, by original designation.
 * Acanthoclinea raised to genus: Brown, 1950e: 249.
 * Acanthoclinea junior synonym of Dolichoderus: Taylor & Brown, D.R. 1985: 93; Shattuck, 1992c: 66.
 * DICERATOCLINEA [junior synonym of Dolichoderus]
 * Diceratoclinea Wheeler, W.M. 1935c: 69 [as subgenus of Dolichoderus]. Type-species: Dolichoderus scabridus, by original designation.
 * Diceratoclinea raised to genus: Brown, 1950e: 249.
 * Diceratoclinea junior synonym of Dolichoderus: Taylor & Brown, D.R. 1985: 93; Shattuck, 1992c: 66.
 * HYPOCLINEA [junior synonym of Dolichoderus]
 * Hypoclinea Mayr, 1855: 377. Type-species: Formica quadripunctata, by subsequent designation of Wheeler, W.M. 1911f: 165.
 * Hypoclinea junior synonym of Dolichoderus: Forel, 1878: 386.
 * Hypoclinea revived from synonymy as subgenus of Dolichoderus: Emery, 1894c: 234; retained as subgenus: Wheeler, W.M. 1910g: 142; Emery, 1913a: 10; Wheeler, W.M. 1915h: 77; Forel, 1917: 247; Borgmeier, 1923: 84; Clark, 1930b: 252; Creighton, 1950a: 331; Kusnezov, 1959: 50; Smith, D.R. 1979: 1415; Kupyanskaya, 1990: 154.
 * Hypoclinea revived status as genus: Kempf, 1972a: 118; Lattke, 1987: 259; Dlussky & Fedoseeva, 1988: 78.
 * Hypoclinea junior synonym of Dolichoderus: Shattuck, 1992c: 66.
 * KARAWAJEWELLA [junior synonym of Dolichoderus]
 * Karawajewella Donisthorpe, 1944b: 59. Replacement name for Diabolus Karavaiev, 1926d: 424. [Junior homonym of Diabolus Gray, J.E. 1841: 400 (Mammalia).]
 * Karawajewella junior synonym of Dolichoderus: Shattuck, 1992c: 66.
 * MONACIS [junior synonym of Dolichoderus]
 * Monacis Roger, 1862a: 233. Type-species: Formica bispinosa, by subsequent designation of Wheeler, W.M. 1911f: 167.
 * Monacis junior synonym of Hypoclinea: Mayr, 1862: 704.
 * Monacis junior synonym of Dolichoderus: Forel, 1878: 386; Dalla Torre, 1893: 156.
 * Monacis revived from synonymy as subgenus of Dolichoderus: Emery, 1894c: 228.
 * Monacis revived status as genus: Brown, 1950e: 249; Kempf, 1959b: 227; Kempf, 1972a: 141.
 * Monacis junior synonym of Dolichoderus: Shattuck, 1992c: 66.
 * MONOCERATOCLINEA [junior synonym of Dolichoderus]
 * Monoceratoclinea Wheeler, W.M. 1935c: 68 [as subgenus of Dolichoderus]. Type-species: Dolichoderus (Hypoclinea) monoceros, by original designation.
 * Monoceratoclinea raised to genus: Brown, 1950e: 249.
 * Monoceratoclinea junior synonym of Dolichoderus: Shattuck, 1992c: 66.

Taxonomic Notes
Dolichoderus is the largest genus in the subfamily Dolichoderinae and has a complex taxonomic history. It has been treated as either a single genus (Forel 1878b, Wheeler and Wheeler 1985), or as many as seven separate genera (Brown 1950). Recent authors have generally recognized two or three genera (Brown 1973, Snelling 1981, Holldobler and Wilson 1990).

All species of Dolichoderus share the characters listed in the Diagnosis above. Additionally, many have large dorsal mesosomal spines and well developed sculpturing (at least for a member of the Dolichoderinae). The development of an anterolateral expansion on the hypostoma and a convex anteromedial margin of the mesosternum are unique to the genus. These characters occur to varying degrees in all species examined in this study. Additionally, the structure of the proventriculus in Dolichoderus is unique within Dolichoderinae, although it is similar to some members of Formicinae.

The diverse views on the internal classification of Dolichoderus result from the rather striking variation in gross body shape, as well as the development of spines on various regions of the mesosoma. However, by classifying on the basis of spine development and overall shape, the phylogenetic relationships among the subgroups have been obscured. For example, there are no characters by which to define Hypoclinea, other than as an assemblage of taxa left after all distinctive groups are removed. Additionally, there are morphological clines between species previously placed in Hypoclinea and Karawajewella, and Hypoclinea and Monacis. These clines make placement of individual species within these groups difficult or arbitrary.

For example, an examination of Hypoclinea reveals that the species Dolichoderus gibbifer (and Dolichoderus feae), Dolichoderus coniger and Dolichoderus brevithorax form a graded series with increasing development of mesonotal spines, linking typical Hypoclinea with the well developed bifurcating spines found in Dolichoderus cuspidatus, the type species of Karawajewella. Similarly, Dolichoderus debilis, a species placed in Monacis, differs from typical Hypoclinea only in possessing pronotal spines. However, the queens of this species lack pronotal spines and are thus inseparable from Hypoclinea (strict sense) queens.

On the other hand some of the groups are phenetically distinct from Hypoclinea. The groups Acanthoclinea (paired spines on both the pronotum and propodeum), Diceratoclinea (paired spines on propodeum only), Monoceratoclinea (a single spine on the propodeum) and Dolichoderus (strict sense) (elongate mesosoma) are clearly distinguishable. The spinal development characterizing the former three groups is distinct. Similarly, the mesothoracic elongation of Dolichoderus (strict sense) separates it from other members in the group for all size classes. While these groups are discernible their treatment as genera is still unacceptable as this would leave Hypoclinea paraphyletic. Therefore all groups are treated as members of the single genus Dolichoderus.

It should be stressed that the recognition of any of these groups of species is recommended only as a matter of taxonomic convenience as some may not form monophyletic groups. In fact, as discussed above, the species previously placed in Hypoclinea are almost certainly paraphyletic and an artificial aggregation of species. Additionally, it seems quite likely that detailed species-level studies will reveal additional sets of morphologically similar species, especially in the diverse Indo-Australian fauna.

Much of the species-level taxonomic work in Dolichoderus has been regional. The species formerly placed in Dolichoderus (strict sense) were reviewed by Kempf (1969), while those placed in Monacis were revised by Kempf (1959) with additional notes by Lattke (1986) and Harada (1987). The Australian fauna was examined by Clark (1930), while the North American species were reviewed by Johnson (1989a) and the east Asian species by Yasumatsu (1941). The remainder of the genus has received little attention, and there is serious need for a world-wide revision of the entire genus.