Anochetus armstrongi

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Anochetus armstrongi
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Ponerinae
Tribe: Ponerini
Genus: Anochetus
Species: A. armstrongi
Binomial name
Anochetus armstrongi
McAreavey, 1949

Anochetus armstrongi casent0172378 profile 1.jpg

Anochetus armstrongi casent0172378 dorsal 1.jpg

Specimen labels

This is one of the more widely distributed Australian Anochetus species, occurring from central Queensland south to southern South Australia. It is also the only species occurring in the cooler south-eastern part of the country.

Biologically, these ground nesting ants are found in a range of drier habitats including dry sclerophyll and savannah woodlands, Callitris forests, Casuarina flats, mallee, bluebush steppes and grasslands. They are almost always found as ground foragers or nesting under a wide range of objects on the ground. Workers forage both day and night.

Photo Gallery

  • Worker feeding during a termite nuptial flight, South Australia. Photo by Mark Newton.
  • Worker feeding during a termite nuptial flight, South Australia. Photo by Mark Newton.
  • Worker feeding during a termite nuptial flight, South Australia. Photo by Mark Newton.
  • Worker feeding during a termite nuptial flight, South Australia. Photo by Mark Newton.

Identification

Entire body smooth and shining except for the sculpturing between the frontal carinae and scattered very weak striations on the propodeal dorsum; eyes large (eye length > 0.30mm). The only other Australian species of Anochetus to show similar lack of sculpturing to A. armstrongi is Anochetus avius. Anochetus armstrongi can be separated from this species by its larger eye size (eye length > 0.30mm vs. < 0.25mm), and longer scapes (scape length > 1.05mm vs. < 1.00mm) and legs (mid-tibial length > 0.85mm vs. < 0.80mm, hind femur length > 1.18mm vs. < 1.10mm). It is very similar to Anochetus renatae but differs in having more weakly developed sculpturing on the propodeum, reduced number of erect hairs on the hind tibiae and less bulging eyes. Anochetus armstrongi is also allopatric to both of these species, occurring in south-eastern Australia while A. avius is limited to northern Western Australia and A. renatae is only known from southern Western Australia.

Keys including this Species

Distribution

Distribution based on Regional Taxon Lists

Australasian Region: Australia (type locality).


Distribution based on AntMaps

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Distribution based on AntWeb specimens

Check data from AntWeb

Biology

Not much is known about the the biology of Anochetus armstrongi but we can presume that its biology is similar to other Anochetus species. The following account of Anochetus biology is modified from Brown (1968):

Habitat. The places where Anochetus live are varied. Where they penetrate into the temperate zone, most species excavate nests in the earth. Occasionally the nest is dug under a covering rock. In the tropics, many nests are also dug in the soil, but in moist forested areas, a common site is the soil beneath a rotting log or other large mass of rotting wood, with extensions of the nest into the log itself. Another frequent nesting site in tropical forest is in the humus and leaf litter at the base of large trees, particularly between buttress roots. Anochetus species of medium or small size often nest in small pieces of rotting wood or bark, or even small rotting twigs or seeds and nuts lying in or on the forest litter. Some species tend to choose more arboreal nest sites.

Diet. Foraging for living animal prey takes place on the soil surface, within the soil-humus-log mold matrix, or on the trunks, branches and foliage of trees and plants wherever these are available. Fragmentary evidence indicates that most epigaeically foraging tropical Anochetus tend to do their foraging at dusk, at night, or during dawn hours. I found Anochetus africanus walking on tree trunks only at night in the Ivory Coast. Some species, particularly those with red heads or other aposematic coloration, apparently forage in the open more during the day. No systematic comparative study has yet been made of foraging hours for different species.

The food of Anochetus consists principally of living arthropods caught and killed or incapacitated by the ants. The smaller and more delicate species Anochetus inermis has been observed by me in a laboratory nest. The colony came from a piece of rotten wood from the floor of a wet ravine near Bucay in western Ecuador. The colony was fed with small tenebrionid beetle larvae (Tribolium castaneum), comparable in size to the A. inermis workers, and the latter attacked the prey with their mandibles in the familiar snapping manner, but very cautiously and nervously, with stealthy approach, extremely rapid strike, and instant recoil-retreat. After several attacks of this kind, with intervening periods of waiting, during which the beetle larvae fled, rested, or writhed about in distress, an ant would finally attack with its mandibles and hold them closed on the prey for long enough to deliver a quick sting in the intersegmental membrane. After this, the prey appeared to be paralyzed, or at least subdued, and sooner or later was carried off by the ant to the nest, and eventually placed on an ant larva.

Frequent delays and excursions before the prey are finally immobilized and brought to the ant larvae in the nest may well have the function of allowing time for protective allomones of the prey to dissipate. Many tenebrionid adults, including Tribofium, possess potent quinonoid defensive allomones, but the larva is not known to possess quinones in this genus.

Nuptial flight. Although males of different species of Anochetus are commonly taken at light, other species are not. Stewart and Jarmila Peck gave me Malaise trap samples taken in western Ecuador that contained males of several species, but Malaise traps capture both day- and night-flying insects.

Defense. When a nest of any of the larger Anochetus species is breached, some of the workers immediately hide beneath leaves or other objects, while other workers rush about with open jaws, which they snap at foreign objects, or even at leaves and twigs, with an audible tick. On human skin or clothing, a worker will snap her jaws and hold fast to the surface with them, at the same time quickly bringing her gaster around to sting. The sting is long and strong, and to me the effect is shocking and quickly painful.

Most of the smaller and medium-sized Anochetus species feign death when disturbed, crouching flat against the surface, or rolling themselves into a ball and remaining still, often for a minute or more. Only when held do they sting. Their stings can be felt in most cases, but the effect is usually trifling.

Castes

Worker

Nomenclature

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

  • armstrongi. Anochetus armstrongi McAreavey, 1949: 1, figs. 1-6 (w.q.) AUSTRALIA. See also: Brown, 1978c: 597; Shattuck & Slipinska, 2012: 7.

Type Material

Taxonomic Notes

Brown (1978) and Heterick (2009) included southern Western Australian specimens as part of this species but these are here considered to belong to the separate species Anochetus renatae. Brown did, however, speculate that these western populations may represent a separate species and listed a number of characters that differ from more eastern specimens. He was reluctant to separate them because of the relatively large amount of morphological variation present and the few specimens available for study. Fortunately the situation has improved since then and the presently available material clarifies the taxonomic significance of the characters Brown discussed. It is now possible to develop well defined diagnoses to separate the eastern and western populations and the present evidence suggests that two separate but similar species are involved. As such the western populations are removed from A. armstrongi to the newly described species A. renatae.

Brown (1978) also discussed specimens from northern Western Australia which he treated as belonging to A. armstrongi but Bob Taylor (pers. comm.) described as being "rather like paripungens". In fact these specimens are not part of A. armstrongi but are here considered as belonging to two separate species, Anochetus avius and Anochetus veronicae.

Description

Worker description. Sculpturing on front of head extending slightly beyond eyes. Scapes not reaching posterolateral corners ('lobes') of head; with limited pubescence and few erect hairs. Pronotum smooth and shining. Mesonotum and metapleuron without sculpture, smooth and shining. Propodeum flattened dorsally, with weak transverse striations and only a few scattered very short hairs. Propodeal angle distinct, triangular. Petiolar node in anterior view truncate or weakly concave. Hind tibiae with erect hairs limited to outer surfaces. Colour yellow-brown or light brown with legs yellow or yellow-brown.

Measurements. Worker (n = 12): CI 94–98; EI 24–27; EL 0.33–0.39; HL 1.36–1.57; HW 1.33–1.51; HFL 1.33–1.46; ML 1.69–1.89; MandL 0.67–0.75; MTL 0.95–1.14; PronI 57–60; PronW 0.77–0.87; SL 1.16–1.32; SI 85–92.

References