Colobopsis gasseri

These arboreal ants are known to nest in a wide range of tree species. They will also nest in houses and similar structures, utilising pre-formed cavities as nest sites.

Identification
A member of the Camponotus macrocephalus species-group. This group has the following characters:


 * Fore femurs swollen, much greater in diameter than middle and hind femurs, generally more swollen than in most other Camponotus species.
 * Spines or bristles on the lower surfaces of the tibiae lacking, or at most, only one or two (most Camponotus species possess two rows of 5 to 10 spines).
 * Major workers and queens with the anterior of the head is truncated and flattened (phragmotic).
 * Major and minor workers present, but not intermediate-sized workers (worker caste dimorphic).

Within this group, this species can be diangosed as follows:

A few erect setae on the front of the head and gaster; none elsewhere. Mesosoma glossy with propodeum raised to hemispherical dome.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Biology
McArthur & Shattuck (2001) note that Camponotus gasseri minor workers are often observed foraging on trunks of eucalypts in the Adelaide metropolitan area. On 20 Jan 1999, A.J. McArthur when watching the removal of a large live Eucalyptus camaldulensis Dehnh at Glen Osmond, a south-eastern suburb of Adelaide, collected a sawn off log which housed a colony of C. gasseri. The diameter of the log was 120 mm and the ants' entrance was nearly 2 mm in diameter, at the junction of a dead offshoot of the log. On cutting open the log, 1142 workers, three dealate queens, one alate male and numerous eggs and naked larvae were found. The volume of the gallery, measured by filling it with water, was 125 ml. About 10 ml of frass resembling sawdust was also taken from the gallery. The gallery appeared to have been excavated by termites (determined by examination of the frass, P. Gleeson, pers. comm. 1999) and was located in the central heart wood and extended for about 300 mm, with the entrance tunnel about equidistant from each end. The width of the main gallery was about 10 mm diameter at the centre. Most of the ants were jet black with a little red at the anterior head, the amount of red being variable. In a few individuals the black was replaced by yellow-brown.

Wheeler (1934) described nests of C. gasseri near Perth, Western Australia in branches of varying sized Leptospermum spp., Acacia spp., Eucalyptus spp. and Callitris spp. Most of the specimens of C. gasseri examined here have been collected while the ants were foraging on vegetation, except for one collection from a pitfall trap and one from leaf litter and those collected from the sawn off log described above.

Nomenclature

 *  gasseri. Colobopsis gasseri Forel, 1894e: 233 (s.w.) AUSTRALIA. Forel, 1902h: 507 (q.); Wheeler, G.C. & Wheeler, J. 1953e: 190 (l.). Combination in Camponotus (Colobopsis): Forel, 1902h: 507; Forel, 1912i: 90. Senior synonym of caloratus, lysias, obtusitruncatus: McArthur & Shattuck, 2001: 31.
 * obtusitruncatus. Camponotus (Colobopsis) gasseri r. obtusitrumcatus Forel, 1902h: 508 (s.w.q.m.) AUSTRALIA. [C. gasseri subsp. obtusitruncatus: Emery, 1925b: 148; justified emendation of spelling.] Junior synonym of gasseri: McArthur & Shattuck, 2001: 31.
 * lysias. Camponotus (Colobopsis) gasseri var. lysias Forel, 1913g: 193 (w.) AUSTRALIA. Junior synonym of gasseri: McArthur & Shattuck, 2001: 31.
 * caloratus. Camponotus (Colobopsis) gasseri subsp. caloratus Wheeler, W.M. 1934d: 162 (s.w.q.m.) AUSTRALIA. Junior synonym of gasseri: McArthur & Shattuck, 2001: 31.

Type Material


Wheeler (1934) described the subspecies coloratus based on "smaller average size and different colour pattern" and admitted that it was "only a slight variant of the typical form." Forel (1913) described the subspecies lysias as "differing in head shape from C. gasseri but otherwise identical with the type". Forel (1902) established the subspecies obtrusitruncatus based on slight differences in head and mesosoma shape, sculpturing and colour, with the minor worker "having a shorter head and more convex pro-mesonotum, with the rest identical" to the typical form. McArthur & Shattuck (2001) can find little to support the retention of any of these subspecies because the differences are trivial. Camponotus gasseri specimens collected at Beerwah, Queensland were light brown and smaller than those collected at Glen Osmond, South Australia. The stated differences in major workers are of little value in diagnosing these forms as they seem to be based on allometric variation within this caste rather than species-level differences.

Description
From McArthur and Shattuck (2001):

Major worker
Whole ant varies from black with patches of red or red brown to occasionally all red. In lateral view. Head: Side without erect setae, posterior three quarters, very finely punctate; anterior quarter striate, truncation 135° abrupt; vertex with a few setae; underside of head without setae. Pronotum and mesonotum forming rounded symmetrical hump, slightly flattened on top, without setae. Metanotum: Two distinct transverse sutures at bottom of a trough, spiracle directed upward, placed below dorsum. Propodeum: Without setae, dorsum hemispherical dome; angle rounded; declivity straight; ratio dorsum/declivity approximately 1; spiracle placed midway between dorsum and coxa, surrounded by fine reticulations and very sparse, short, fiat-lying, coarse setae. Node: Finely reticulate, glossy, without pilosity; anterior face mostly straight; summit rounded; posterior face mostly straight. Gaster: Very finely striate, no pubescence, few short setae along membranes. Fore femur: Swollen. Mid tibia: Without erect setae, with very sparse, indistinct, flat-lying setae without bristles inside. In dorsal view. Head: Sides, posterior half straight, parallel; anterior half slightly convex, tapering to the front; vertex flatly convex, widely rounded corners; scape without erect setae; frontal carinae wider than half HW; frontal area indistinct, max 11W posterior to eye centre; mandibles with many fine teeth. Clypeus: Coarsely striate longitudinally, without pubescence, carina replaced with groove; anterior margin convex, narrow, projecting. In front or rear view. Node: Wide, summit widely bidented, without setae.

Minor worker
Whole ant varies from black with patches of red or red brown to occasionally all red. In Lateral view. Head: Side, glossy, finely reticulate with sparse, short, flat-lying setae; vertex with a few long setae; underside of head without setae. Mesosoma and node without erect setae or pubescence. Pronotum and mesonotum humped forming even convexity higher than metanotum. Metanotum: Deep wide trough with convex base; prominent spiracles pointing upward, placed near level of dorsum. Propodeum: Elevated, high, humped, evenly convex; angle well rounded; declivity mostly straight; ratio dorsumldeclivity approximately 1; spiracle placed midway between dorsum and coxa, pointing rearward, surrounded by glossy, finely reticulate integument. Node: Anterior face lower half straight, upper convex; summit rounded; posterior face straight. Gaster: Microscopically striate. Fore femur: Swollen. Mid tibia: Sparse short, fine, adpressed setae, without bristles inside. In dorsal view. Head: Sides, flatly convex, tapering to front; vertex and angles uniformly convex; scape without erect setae, with indistinct adpressed setae. Frontal carinae short, very wide apart, mostly diverging; frontal area indistinct; max HW at eye centre. Clypeus: Wide, without truncation, few setae on margins, glossy, finely punctate-reticulate; carina distinct; anterior margin convex. In front or rear view. Node: Summit flatly convex, wide, without setae.

Measurements
HW 0.90-1.60 mm, HL 1.00-1.70 mm, PW 0.65- 1.20 mm, TL 0.90-1.10 mm.

Camponotus gasseri

Worker major. Length 6.5 mm.

Mandibles short, obtuse, armed with about 7 teeth, dull, a little silky, abundantly punctate, densely striated wrinkled lengthwise, and in addition finely reticulate-punctate. Head is distinctly longer then wide and wider behind than in front, in the form of a trapeze, and at the posterior border slightly concave (almost straight). Eyes situated at the posterior fourth of the head near the sides. The head is truncated at the front. The truncated surface is small, short, concave, less raised up than the front and does not reach the sides of the head and comprises only the middle part of the cheeks; It is at least two times wider than long and is not distinctly bordered. The clypeus is strongly indented in two places in front, rounded in the middle, a little projecting at the middle of the anterior border,at the middle..........a little wider behind than at the front, provided with a large median longitudinal furrow at the bottom of which is found a small longitudinal ridge. The portion of the clypeus situated behind the truncation is at least twice as wide as long. The frontal area is small, insignificant. Frontal ridges are wide apart, very divergent converging towards the border of the head. There are 3 distinct pits in place of the occelli.vThe antennae are thick and short. The segments 5 to 10 of the funiculus are scarcely as long as wide.

The thorax short, very rounded and very convex in all directions. Profoundly indented between the mesonotum and metanotum (= propodeum?); the intermediary segment is very short and is situated entirely at the bottom of the indentation. The pronotum and mesonotum combine to form a strong hump, a little longer than wide. The pro-mesonotal suture is deeply impressed. The metanotum (= propodeum?) forms at its side also a strong and short hump wider than long which does not show a distinct boundary between the basal face and the declivity; the declivity is the longer. The node is low, thick, very wide (twice as wide as high) very wide at the summit which is widely indented and thick. Gaster large, elongated. The limbs are short, subcylindrical and rather thick. The tibias are without small barbs.

Moderately glossy, rather feebly shagreen (Transversely wrinkled on the gaster, reticulated on the thorax and the back of the head). Punctation sparse, piligerous, distinct on the head and still visible on the thorax but not on the gaster. The anterior 2/3 of the head is dull or silky, densely finely reticulate punctate. From the insertions of the antennae up to the outside border, the front of the head in addition is grossly wrinkled or striated lengthwise. At the front, the striations are more fine and closer together; at the sides and only passes the truncation by a little. Pilosity erect sparse and almost absent. Some yellow setae at the two extremities of the body. Flat lying pubescence extremely short, very sparse, situated at the base of the sparse barbs, more visible on the limbs and on the scape, none on the gaster. Of a brownish black. Limbs and scapes brown. The front of the head, the mandibles and segments of the antennae a darkish red or red-brown. The segments of the gaster are bordered yellow-red. Queen. Length 4.2 to 4.5 mm.

Mandibles narrowed, glossy, scarcely punctated, armed with 5 to 6 teeth ?. The form of the head is similar to the major worker, but without truncation and with a convex clypeus, without a keel, sublobed (wide lobe rounded and very short), with a distinct median impression in the posterior third. Antennae thick. Segments 8 to 10 as wide as long. The scape surpasses the occiput by 1/5 of its length. The frontal ridges are wide apart, more wide apart than they are long, they are nearer to the central ridge than the sides of the head. The head is wider behind than in front and is a little convex at its posterior border.

Thorax as in the major worker, but the mesonotum is much more narrow and much less convex. The indentation is still deeper and above all wider; in the prominent middle of the dorsum there are 2 stigmata, like 2 sharp teeth. The metanotum (= propodeum) forms a hump still stronger and more elevated than the major worker, also as wide as long and with a strong declivity as convex in front as behind. Node very thick, very short, wide, thick and convex at the summit (no indentation). The rest is like the worker major but the front of the head is rather glossy or sub-opaque and does not have the large wrinkles and is reticulated (but not reticulate-punctate). Some setae on the head and on the back of the gaster. Completely black, with mandibles of a yellowish red, the limbs and scapes of a very dark brown, the funiculus and the articulations of the limbs are a light reddish brown and just the segments of the gaster are bordered yellow. The rest is identical with the worker major. Perth, Western Australia. (M Chase)

Camponotus gasseri coloratus Soldier: Length 5-6.5 mm.

Differing from the typical gasseri in its smaller average size, smaller head, less convex pro and mesonotum, shallower metanotal impression, slightly thinner and dorsally less obtuse petiolar scale and in coloration, the red of the anterior portion of the head being more vivid, or more yellowish and extending further back of the truncation over the cheeks and the whole front. The vertical portions of the thorax and petiole, and the dorsal sutures of the former red or reddish brown and the bases of the first and second gastric segments are ivory yellow. The antennae and legs are also distinctly paler being red or brownish red. Worker: 3-4 mm.

Although smaller than the worker gasseri, with the same differences as the worker in the coloration of the thorax and appendages, the cheeks and often also the clypeus yellowish red or reddish yellow like the mandibles. In some specimens only the posterior half of the head is dark brown or black and the thorax is red, with only the discal portions of the pro-,meso- and epinotum black. Female (dealated). Length about 7 mm.

Decidedly smaller than the female of typical gasseri which measures 9 mm. Coloration like that of the soldier, but with only the sutural regions reddish. the ivory yellow portions of the first and second gastric segments are more extensive and the third segment has an ivory spot at the base of each side. Male. Length 4.5 mm.

Black with very dark brown legs and antennal scapes; mandibles, funiculi and genitalia dull piceous; wings whitish with pale brown veins and pterostigma. Fore femora strongly bowed. Described from many specimens from several populous colonies found nesting under the bark of Leptospermum, Callitris and Acacia trees near Government House (X.22.'31). The nest entrances were small, perfectly circular holes in the bark. No doubt, these entrances are guarded by soldiers as in other species of Colobopsis.

C. gasseri was originally described from Perth. I have taken specimens near Pemberton, Western Australia, nesting in the branches of a huge recently felled Karri tree (Eucalyptus diversicolor), and have received others collected by Mr John Clark at Mundaring Weir. The species is widely distributed over southern and eastern Australia from Queensland to Tasmania. The Tasmanian form was described by Forel as var. lysias, that from Queensland as subsp. obtusitruncatus. The specimens which I have taken in New South Wales and have received from several localities in South Australia are only slight variants of the typical form from Western Australia.

Camponotus gasseri lysias Worker Length: 7 mm.

Different from the type by its shorter head, almost as wide in front as it is behind. The part situated behind the truncated portion is a little wider than long. Each of the halves of the clypeus which are located behind the truncated portion is distinctly wider and long. Otherwise identical with the type. Worker Length 4 to 4.6 mm.

Also differs from the type by its head being shorter and wider, almost as wide as long and as wide in front as it is behind. (Lea)

Camponotus gasseri obtrusitruncatus

Worker major. Length 5.8 to 7 mm.

Differs from the type by its truncated surface of the head which instead of being concave and bordered by a sharp border or a sharp edge is only obtusely bordered or sub-bordered and more or less flat. Furthermore this surface as well as the frons is simply finely reticulate punctate with large sparse punctures, but without any striations or longitudinal ridges. For the rest of the head as in the type but of a more vivid red in front. The pro-mesonotum and the metanotum (= propodeum) are even more strongly convex, separated one from the other by a deep groove with a flat bottom which is wider than in the type gasseri, this bottom is made up of an intermediate segment which is strongly developed. Worker minor. Length 3.5 to 4 mm.

The head is shorter than in the type gasseri. Pro-mesonotum more convex. The rest is identical. Queen. Length 7.8 mm.

Same differences of the head as with the major. Pale color more concentrated to the first segments of the abdomen. Wings veins,spots and stigmata brown. Male. Length 4.5 to 5 mm.

Head as wide as long. Metanotum fairly convex. Entirely black; the limbs and antennae a dark brown. Mackay, Queensland (turner)