Ocymyrmex foreli

AntWiki - Where Ant Biologists Share Their Knowledge
Jump to: navigation, search
Ocymyrmex foreli
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Myrmicinae
Tribe: Crematogastrini
Genus: Ocymyrmex
Species: O. foreli
Binomial name
Ocymyrmex foreli
Arnold, 1916

Ocymyrmex foreli casent0235947 p 1 high.jpg

Ocymyrmex foreli casent0235947 d 1 high.jpg

Specimen Labels

Forder and Marsh (1989) found that O .foreli colonies contained 160 to 1586 adults, of which 4 to 20 per cent were ergatoid females. Only one inseminated female occurred per colony, and that female was distinguished by her physogastry. Ergatoid females, even when unmated, had significantly more ovarioles than workers, and mated females had more than virgins. The behavioural repertoire of virgin ergatoids was approximately the same as that of the workers but varied with respect to the frequencies with which the various behaviours were performed. They also noted that ergatoid females were produced throughout the year, but that colony production was positively correlated with mean monthly rainfall.

Identification

A member of the weitzeckeri group. Related to Ocymyrmex sobek with which it shares the character of possessing a massively developed petiole node which is coarsely sculptured. The two are separable on colour pattern as in sobek the alitrunk is dark reddish brown to almost black, the gaster yellow and contrasting strongly with the alitrunk. The head is dull red, intermediate in colour between alitrunk and gaster. Beside this, the sculpture on the petiole is more sharply defined and regular in foreli than in sobek. (Bolton 1981)

Keys including this Species

Distribution

Distribution based on Regional Taxon Lists

Afrotropical Region: South Africa, Zimbabwe (type locality).

Distribution based on AntMaps

AntMapLegend.png

Distribution based on AntWeb specimens

Check data from AntWeb

Biology

Bolton and Marsh (1989) - Nests of foreli typically have one entrance that opens into a vertical tunnel which terminates in a broad chamber at a depth of about 30 cm. Other brood and food chambers branch off from the tunnel at various intermediate levels.

Observations by one of us (Marsh) indicate that nest digging is a regular part of the diurnal behaviour repertoire of Ocymyrmex species and that nest relocation is common. Typically such relocations involve the entire colony and entail a move to a new nest very close to the original nest. For example, a mass emigration in 1986 of an O.foreli colony was carefully documented by Alves and Marsh (unpublished). For three weeks prior to the emigration most activity involving individual and group forays from the nest occurred towards a specific site 4 m away, where the ants were excavating a new nest. Finally, during the course of a single day, the entire colony relocated to the new nest. Brood, callows and intra-nidal individuals were carried to the nest by the extra-nidal individuals. The reason for mass emigration and nest relocation is not known. It would appear that the ants consider the original nest to be unsuitable but that the foraging area itself remains suitable. Colony fission, in contrast, involves movements over considerably greater distances away from the centre of the foraging area of the mother colony. Thus it seems likely that a recently inseminated ergatoid excavates a new nest with the help of some recruited nest-mates before colony fission occurs.

Castes

Worker

Nomenclature

The following information is derived from Barry Bolton's New General Catalogue, a catalogue of the world's ants.

  • foreli. Ocymyrmex weitzeckeri var. foreli Arnold, 1916: 197 (w.) ZIMBABWE. Bolton, 1981b: 261 (q.); Bolton & Marsh, 1989: 1279 (m.). Raised to species: Bolton, 1981b: 269. See also: Forder & Marsh, 1989: 106.

Unless otherwise noted the text for the remainder of this section is reported from the publication that includes the original description.

Description

Worker

Bolton (1981) - TL 7.3-8.0, HL 1.76-1.86, HW 1.64-1.76, CI 92-95, SL 1.56-1.72, SI 92-98, PW 1.08-1.14, AL 2.28-2.44 (14 measured).

Anterior clypeal margin with a semicircular impression but this impression frequently shallower and broader than is usual in the genus; flanked by a pair of low broad tubercles or blunt small teeth formed by a thickening of the clypeal apron. Maximum diameter of eye 0.34-0.36, about 0.20-0.22 x HW. Promesonotum in profile evenly shallowly rounded and convex. Propodeal dorsum more or less flat to slightly convex, rounding broadly and evenly into the declivity. Metapleural lobes small and rounded. Petiole node in profile large, almost or quite as massively developed as in sobek. In dorsal view the petiole node appearing swollen, as broad as or broader than long; postpetiole dorsally as broad as long, discounting the anterior articulatory section. Base of first gastral tergite constricted and forming a neck behind the postpetiole. Dorsum of head finely and densely longitudinally regularly costulate-rugulose, the components sharply defined and parallel. On the central part of the dorsum the sculpture is longitudinal, running straight back to the occiput or at most diverging slightly on each side of the occipital impression. More laterally on the dorsum the rugulae are divergent and arch outwards behind the eye. Ground-sculpture of head finely punctulate or granular. Pronotal dorsum usually with arched-transverse costulate sculpture followed by a patch of longitudinal sculpture which runs back between the mesothoracic spiracles. However, in some workers the sculpture here is oblique and in a few is more or less transverse. Remainder of dorsal alitrunk and also propodeal declivity transversely costulate or rugose. Petiole node coarsely sculptured everywhere, with strong, sharply defined rugae which encircle the node, running continuously across the dorsal and ventral surfaces and down the sides. Peduncle of petiole also with transverse rugulae both dorsally and ventrally, but these are weaker or effaced on the sides. All dorsal surfaces of head and alitrunk with numerous hairs; first gastral tergite also with hairs but these are shorter and much sparser than those on the alitrunk. Colour usually uniform orange-red to red throughout, but sometimes the gaster slightly lighter or darker than the alitrunk.

Type Material

Syntype workers, Zimbabwe: Redbank, 7.iv.1912 (G. Arnold) (The Natural History Museum; NM, Bulaway) [examined].

References