Cataulacus egenus

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Cataulacus egenus
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Myrmicinae
Tribe: Crematogastrini
Genus: Cataulacus
Species: C. egenus
Binomial name
Cataulacus egenus
Santschi, 1911

Cataulacus egenus casent0178292 profile 1.jpg

Cataulacus egenus casent0178292 dorsal.jpg

Specimen labels

Synonyms

Nests of Cataulacus egenus have been found in rotten branches of cocoa trees that are still attached to the trunk. The workers forage actively upon the bark and leaves but their diet is unknown.

Identification

A member of the huberi group. This species is most closely related to Cataulacus huberi, sharing the same pedicellar and gastral development, but is separated from it by the characters given in the key (Bolton 1974).

Keys including this Species

Distribution

Known from Ghana, Nigeria, Uganda, Zaire.

Distribution based on Regional Taxon Lists

Afrotropical Region: Congo (type locality), Democratic Republic of Congo, Ghana, Kenya, Nigeria, Uganda.

Distribution based on AntMaps

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Distribution based on AntWeb specimens

Check data from AntWeb

Biology

Much of the information concerning the biology of Cataulacus species is anecdotal and fragmentary. Arnold (1917) wrote a succinct general overview of Cataulacus biology that still remains quite informative. Arnold reports "all the species of this genus are tree-ants, usually forming medium sized nests in hollow twigs and stems, or more rarely, under the bark. They are timid and slow-moving insects, often feigning death or dropping rapidly to the ground when disturbed. As Bingham has remarked in connection with this genus (Fauna Brit. India, Formicidae), these ants have the habit of wandering over the trunks of trees and the leaves in what appears to be a very aimless and languid manner. I have occasionally seen them breaking open the earthen tunnels constructed by termites over the trunks of trees and attack the inmates."

Bolton (1974) expands upon this earlier account - "All known Cataulacus species are arboreal or subarboreal nesters and they predominantly forage on the trees and shrubs in which the nests are situated. Very few appear to come down to ground level but in West Africa the small species Cataulacus pygmaeus and Cataulacus brevisetosus may be found foraging in leaf litter or crossing the ground to ascend a tree other than the one in which the nest is situated. The nests themselves are usually constructed in small hollow twigs or stems by the smaller species and in rotten branches or rotted portions of the tree trunk by the larger species. This is rather a generalization as some small species are known which nest in and under rotten bark (e.g. Cataulacus vorticus) and undoubtedly some of the larger forms will eventually be found inhabiting relatively small cavities in plants.

Various species of the genus in Africa are known to inhabit a variety of galls, acacias and bushes as well as large trees. Numerous species have been found nesting in, and have therefore been often collected from, cocoa in Africa. Some of these species are Cataulacus guineensis, Cataulacus pygmaeus, Cataulacus mocquerysi, Cataulacus egenus, Cataulacus vorticus, Cataulacus brevisetosus, Cataulacus kohli and Cataulacus theobromicola. Feeding habits in the genus are mostly unknown but the present author has noted C. guineensis tending aphids and small coccids.

On the plants ants of the genus Cataulacus often occur together with Oecophylla or species of Crematogaster, and appear to be mostly tolerated (at least they are not evicted) by the majority of these forms. Their defence against attackers of these genera lies primarily in their armoured exterior, but their ultimate escape reaction is to curl up and release their grip on the plant, falling to the ground and thus making their escape. The decision to remain immobile and present an armoured surface or to drop from the plant appears to depend upon the size or persistence of the aggressor; larger attackers usually precipitate the latter reaction, but it has also been noted as a result of persistent and unwanted attention by a series of workers of a small Crematogaster species.

The majority of species are forest-dwelling forms, with relatively few adapted to savannah or veldt conditions. Those which do, however, occur in these zones tend to be very successful in their chosen habitat and often possess a wide distribution. A few species are apparently able to exist in any region of Africa providing the basic essentials of nesting-site and food supply are met with, but on the whole the fauna may be divided into forest and non-forest forms."

Some species have nests that can be protected by a single worker's head, as its shape matches the nest entrance and forms an effective plug.

It has more recently been discovered that some species of Cataulacus are efficient gliders (Cataulacus erinaceus, Cataulacus guineensis, Cataulacus mocquerysi and Cataulacus tardus). Workers exhibit directed movement while in freefall that allows them to glide back to regain a hold on the same tree trunk. (Yanoviak et al. 2005, 2007, 2008)

Castes

Nomenclature

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

  • egenus. Cataulacus egenus Santschi, 1911c: 359, fig (w.) CONGO. Wheeler, G.C. & Wheeler, J. 1954b: 151 (l.); Bolton, 1974a: 18 (q.m.). Senior synonym of simplex: Bolton, 1974a: 18.
  • simplex. Cataulacus egenus st. simplex Santschi, 1914b: 111, fig 18 (w.) UGANDA. Junior synonym of egenus: Bolton, 1974a: 18.

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

Description

Worker

Bolton (1974) - Bolton (1974) - TL 4.2 - 6.1, HL 1.10 - 1.48, HW 1.22 - 1.74, CI 101 - 120, EL 0.40 - 0.48, OI 27 - 33, IOD 1.00 – 1.48, SL 0.62 – 0.80, SI 46 - 52, PW 1.14 – 1.60, AL 1.32 - 176, MTL 0.66 – 0.88 (10 measured).

Occipital crest variously developed; either complete or incomplete medially or absent, the last occurring usually in small workers. When the crest is well developed it is little more than an acute angle separating the vertex from the occiput. Occipital corners with a dentiform angle projecting somewhat laterally or the corners merely acutely angled. Sides of head behind eyes smooth and regular, not denticulate nor crenulate. Pronotum marginate laterally, not denticulate, the margination not or only slightly expanded, either simple and following the shape of the segment or with a small, bluntly rounded dentiform process anteriorly. Remainder of alitrunk not marginate and not denticulate, the dorsum rounding smoothly into the sides. Propodeum with a pair of long, acute, slightly divergent spines. Dorsal alitrunk usually without sutures or with the location of the promesonotal suture indicated by a very faint impression. Rarely the metanotal groove is also indicated by an extremely faint marking upon the dorsum. Petiole with the dorsal surface strongly transverse, rectangular or subrectangular in shape; postpetiole also expanded transversely. First gastral tergite marginate basally and for part of the length of the sides; this structure paralleled on the sternite laterobasally by a raised ridge or carina.

Bolton 1974 fig 1-6
Sculpturation of dorsum of head a fine, dense and very shallow reticulate-puncturation which is often more or less effaced, the whole overlaid by a fine, irregular, usually disorganized rugoreticulum. Pronotal dorsum usually similar to the head with the puncturation more distinct, especially upon the anterior half. Remainder of dorsal alitrunk finely reticulatepunctate with numerous very fine rugulae. These are predominantly longitudinal in direction but often a reticulum is present in places. On the propodeal dorsum the rugulae tend to diverge posteriorly towards the bases of the spines and rarely are they transverse upon the dorsum. Declivity of propodeum usually with some transverse rugulae, at least between the spines. Petiole and postpetiole coarsely transversely rugose or sulcate-rugose, the gaster densely reticulate-punctate with a few longitudinal rugulae.

Erect hairs absent from all dorsal surfaces of head, alitrunk, pedicel and gaster, but a few may be present upon the lateral margins of the head. The appendages bear numerous hairs.

Queen

Bolton (1974) - Bolton (1974) - TL 6.6 – 7.0, HL 1.40 – 1.50, HW 1.42 – 1.58, CI 101 - 105, EL 0.44 – 0.48, OI 30 - 31, IOD 1.20 – 1.34, SL 0.72 – 0.76, SI 48 - 50, PW 1.34 – 1.50, AL 1.88 – 1.92, MTL 0.76 – 0.88 (3 measured).

Answering the description of the worker but with the usual thoracic modifications. Occipital crest usually developed as an angle. Pro notal marginations less distinct, propodeal spines reduced to a pair of short, broad and blunt teeth. Sculpturation basically as worker but the mesoscutellum may lack rugulae and the propodeal dorsum is usually transversely rugulose. The female of this species was first described by Wheeler (I922a: 199).

Male

Bolton (1974) - Bolton (1974) - TL 5.1 – 5.5, HL 0.92-1.00, HW 1.10 – 1.16, CI 116-119, EL 0.36, OI 31 - 32, IOD 0.90 – 0.96, SL 0.48 – 0.50, SI 42 - 43, PW 1.00 – 1.02, AL 1.58 – 1.68, MTL 0.82 – 0.86 (2 measured).

Occipital crest not present, the occipital corners dentiform. Sides of head behind eyes with one or two denticulae. A pair of small, shallow impressions present upon the vertex, situated just behind and laterad of the posterior ocelli, and almost in a straight line between this and the median (anterior) ocellus. Pronotum weakly marginate laterally, the sides almost straight, not denticulate. Anterior arms of notauli developed and cross-ribbed, fading out medially; the posterior arm absent. Propodeum with a pair of short, broad but acute spines. Segments of pedicel in dorsal view developed as in the worker, but less strongly so. First gastral tergite not marginate, the sternite without a carina.

Sculpturation of head reticulate-punctate in the vicinity of the ocelli, but elsewhere also with sparse rugulation which tends to form a reticulum in places. Pronotal dorsum similar to the last, with a marked rugoreticulum; the sc1erites of the mesonotum predominantly reticulate-punctate, with few or no rugulae. Propodeal dorsum coarsely rugose; the segments of the pedicel with marked transverse rugae, especially the petiole. Gaster finely and densely reticulate-punctate. Erect hairs sparse upon the head and alitrunk, numerous on the gaster.

Type Material

Bolton (1974):

Holotype worker, CONGO (BRAZZAVILLE): Madingou (R. P. Zimmermann) (NM, Basle) [examined].

Cataulacus egenus st. simplex. Holotype worker, UGANDA: Central Region, i. 1909 (Ch. Alluaud) (location of type not known).

References

  • Bolton, B. 1974a. A revision of the Palaeotropical arboreal ant genus Cataulacus F. Smith (Hymenoptera: Formicidae). Bull. Br. Mus. (Nat. Hist.) Entomol. 30: 1-105 (page 18, queen, male described)
  • Santschi, F. 1911c [1910]. Nouvelle fourmis d'Afrique. Ann. Soc. Entomol. Fr. 79: 351-369 (page 359, fig. worker described)
  • Wheeler, G. C.; Wheeler, J. 1954b. The ant larvae of the myrmicine tribes Cataulacini and Cephalotini. J. Wash. Acad. Sci. 44: 149-157 (page 151, larva described)