Colobopsis macrocephala

Colobopsis macrocephala is generally found nesting in branches of trees and shrubs in eastern Australia.



Major and minor workers (images by Archie McArthur, SAM (Adelaide)).



A minor worker cleaning its antenna using a special structure on its front leg.

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:

Mandibles in major workers smooth, with shallow fovae, rugae weak and limited to anterior region of dorsal surface of the mandible. Few long, erect setae on head and gaster, none elsewhere. In lateral view, dorsal surfaces of pronotum, mesonotum and propodeum form a continuous weakly convex surface, the posterior propodeal face mostly straight.

Note that the closely related Colobopsis howensis may prove to be conspecific with this species.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Nomenclature

 *  macrocephala. Formica macrocephala Erichson, 1842: 259 (q.) AUSTRALIA. Combination in Iridomyrmex: Taylor & Brown, D.R. 1985: 100; in Camponotus: Shattuck & McArthur, 1995: 122. Combination in Colobopsis: Ward, et al., 2016: 350. Senior synonym of fictor: Shattuck & McArthur, 1995: 122; of augustulus, semicarinata: McArthur & Shattuck, 2001: 38. See also: Shattuck, 1992a: 16.
 * semicarinata. Colobopsis rufifrons r. semicarinata Forel, 1895f: 418 (s.) AUSTRALIA. Combination in Camponotus (Colobopsis): Forel, 1902h: 508. Raised to species: Forel, 1902h: 508. Junior synonym of macrocephala: McArthur & Shattuck, 2001: 38.
 * fictor. Camponotus (Colobopsis) fictor Forel, 1902h: 508 (s.w.) AUSTRALIA. Wheeler, G.C. & Wheeler, J. 1968: 217 (l.). Junior synonym of macrocephala Erichson: Shattuck & McArthur, 1995: 122.
 * augustulus. Camponotus (Colobopsis) fictor subsp. augustulus Viehmeyer, 1925b: 145 (s.w.q.) AUSTRALIA. Material of the unavailable name continentalis referred here: Viehmeyer, 1925b: 145. Subspecies of macrocephala: Bolton, 1995b: 87. Junior synonym of macrocephala: McArthur & Shattuck, 2001: 38.

Taxonomic Notes
Ford (1902) distinguished semicarinatus from macrocephala (as factor) by differences in the shape of the head, propodeum and petiolar node and in having the sculpturing on the truncated portion of the clypeus "more clearly lengthwise and not wrinkled reticulate as in the case of semicarinatus". Viehmeyer (1925) described the subspecies augustulus as having "head of the major worker noticeably narrower than in the type, the truncate surface of the anterior head less sharply delineated and less concave, and the longitudinal grooves of the head and clypeus much stronger". However, the currently available material shows considerable variation in all of these characters and we can find no justification for recognising the subspecies separately from C. macrocephala.

Major worker
In lateral view. Yellow brown, gaster sometimes darker, limbs, especially coxa very much lighter than mesosoma. Head: Side with no erect setae, anterior sharply truncated; posterior glossy, smooth; anterior striations extending from truncation nearly half way to eye; vertex with few long setae; underside of head without erect setae, with very sparse short, flat-lying setae. Mesosoma: Without erect setae. Pronotum and Mesonotum: Evenly convex. Metanotum: Wide trough, spiracle well below dorsum. Propodeum: Dorsum evenly curved, angle rounded; declivity mostly straight; ratio dorsum/declivity, approximately 1; spiracle well forward of declivity, closer to coxa than dorsum, surrounded by indistinct reticulate integument, glossy, without pilosity. Node: Without setae, anterior face lower half straight, upper evenly convex; summit blunt; posterior face straight. Gaster: Glossy, indistinctly striate. Fore femur: Swollen. Mid tibia: Without erect setae, with sparse, flat-lying pubescence, without bristles inside. In dorsal view. Head: Nearly rectangular, sides straight, parallel; vertex straight, angles blunt; scape with very sparse, short, flat-lying setae. Frontal carinae mostly straight, diverging, posterior very wide. Frontal area, very small, depressed; clypeus sides bordered by sharp ridge, narrow, widest at truncation, sides nearly straight, tapering anteriorly, grossly ridged longitudinally, similar to cheeks, three fourths of clypeus anterior to truncation. Anterior head comprising clypeus, mandibles and cheeks lie on flat circular plane; max HW at eye centre; eyes oval. Clypeus: Without erect setae, carina present within striations; anterior margin narrow, projecting, evenly convex. In front or rear view. Node: Summit wide, slightly indented, without setae.

Minor worker
Head: Brownish yellow to brown, limbs and antennae more yellowish, much lighter than mesosoma; side of head, mesosoma, node yellow brown; vertex with few setae; underside of head without erect setae. Mesosoma: Glossy, microscopically reticulate, without pilosity. Pronotum: Anterior and posterior thirds straight, centre third convex. Mesonotum: Mostly straight, slightly raised above pronotum and propodeum. Metanotum: Slight ridge; spiracle near middle of side. Propodeum: Dorsum straight to flatly convex, angle abrupt; declivity nearly straight, ratio dorsum/declivity about 1.5; spiracle situated midway between dorsum and coxa, glossy, surrounded by microscopic reticulation. Node: Without pilosity, anterior face lower half straight, convex above; summit sharp; posterior face straight. Gaster: Finely striate. Fore femur: Swollen. Mid tibia: With indistinct, sparse, short, flat-lying setae, without bristles inside. In dorsal view. Head: Sides straight, slightly tapering to front; vertex and angles form even convexity; scape with indistinct, sparse, short, flat setae; frontal carinae wide, diverging; frontal area indistinct, diamond shaped; max HW just posterior to eye centre. Clypeus: Glossy, finely reticulate, few sparse, erect, setae, carina indistinct; anterior margin, convex, wide, projecting. In front or rear view. Node: Summit wide, sometimes indented, without setae.

Measurements
PW 0.7-1.2 mm, HT 0.8-1.25 mm, EL 0.3-0.4 mm, 11W 0.95-1.7 mm, HL 1.1-1.9 mm, CAR W 0.5-0.8 mm, CLY W 0.5-0.6 mm, TL 0.95-1.0 mm, NW 0.35- 0.65 min.

Original descriptions

Camponotus fictor

Major. Length 6 to 6.7 mm. Head 1/3 longer than wide (1/5 in the case of semicarinatus). Clypeus feebly keeled, extending from one end of the clypeus to the other. The front of the head is clearly wrinkled lengthwise, not rugose (wrinkled-reticulate) in the case of semicarinatus.

QUEEN Length 3.5 to 5 mm. Head elongated, almost a quarter longer than wide (almost square in the case of semicarinatus). In addition the head of the worker is not truncated in front, whereas in the case of semicarinatus it is at least as truncated (obtusely) as C. truncatus queen of Europe; the difference is quite specific. The head of C. fictor minor is like an ordinary. Camponotus head, only the clypeus, is sub-keeled, a strong and rounded lobe which is almost absent in the case of carinatus. The thorax is as convex; the basal face of the metanotum (= propodeum) is longer than the declivity, terminating in a clear strong angle. The face of the declivity is a little concave and edged and ends in a point above the angle which projects even slightly. In semicarinatus, the declivity undergoes an abrupt but rounded curve at the basal face which is much shorter. The metanotum (= propodeum) of C. fictor reminds one of C. conicus Mayr while being much less accentuated.

The node is a little thicker, strongly convex at front, flat at back, with a very sharp edge, slightly indented at the summit. In the case of semicarinatus it is much lower and much less thick. Sculpture (except for wrinkles at the front of the head) pilosity and color are identical with semicarinatus.

New Castle, Native Dog Bore N S Wales (Froggatt)

Formica macrocephala

Dark brown, gray-silky, elongated head, emarginate at the base, testaceous, pale legs.(Female) Length 5 lines.

Closely resembling F. cylindricae Latr., dark brown, sparse (grisea) silky pubescence. Head wider than the thorax, oblong with straight sides, emarginate at the base, the posterior angles are very prominent, punctations overall are feeble and a red brick color. Thorax narrowed, compressed, brick colored underneath. The node is small, low and subemarginate at the apex. The abdomen is rather long, very large and subdepressed dorsally. Legs are a pale brick color. The wings are elongate, transparent, stigmata dark brown, pale nerves, with 3 cubital cells anteriorally and a single discoidal cell.

Colobopsis rufifrons semicarinatus Worker major The truncation of the front part of the head is clear, but its border is obtuse, rounded, not at all sharp, not crenulated. Anterior half of the clypeus is distinctly keeled in the middle, vaguely rugose and depressed, from each side of the keel. The posterior half (situated in part still on the truncated portion) is convex, not at all depressed, strongly wrinkled reticulated lengthwise. The wrinkles converge towards the keel of the anterior portion which serves them as a stem. Declivity of the metanotum (= propodeum) 2.5 times the basal face (intermediary segment not compressed). Of a dirty yellow, uniform, a little brownish. Abdomen is a yellowish brown, front of head reddish. Apart from that, this insect corresponds with descriptions both Smith and Mayr give to C ruffifrons but I do not know whether this specimen is sufficiently distinct. Mackay, Queensland (Gilbert Turner)

Measurements
PW 1.0 mm, HT 1.2 mm, EL 0.4 mm, HW 1.4 mm, HL 1.8 mm, CAR W 0.8 mm, CLY W 0.6 mm, TL 0.9 mm, NW 0.55 mm.


 * CAR W = maximum frontal carina width
 * CLY W = clypeus width measured between tentorial pits
 * EL = eye length in dorsal view
 * HW = maximum head width in dorsal view
 * HT = maximum head thickness in lateral view
 * HL = head length measured from anterior margin of clypeus to vertex
 * PW = maximum pronotal width in dorsal view
 * NW = node width in dorsal view
 * TL = length of mid tibiae.

Taxonomy
Forel (1902) distinguished semicarinatus from macrocephalus (as fictor) by differences in the shape of the head, propodeum and petiolar node and in having the sculpturing on the truncated portion of the clypeus “more clearly lengthwise and not wrinkled-reticulate as in the case of semicarinatus.” Viehmeyer (1925) described the subspecies augustulus as having “head of the major worker noticeably narrower than in the type, the truncate surface of the anterior head less sharply delineated and less concave, and the longitudinal grooves of the head and clypeus much stronger”. However, the currently available material shows considerable variation in all of these characters and we can find no justification for recognising the subspecies separately from C. macrocephalus.