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Tetramorium grassii Emery 1895

Compiled by Warwick Don & Richard Harris
Biostatus: Introduced


Family:  Formicidae
Subfamily:  Myrmicinae
Tribe:  Tetramoriini
Genus:  Tetramorium
Species:  grassii

Common name(s) 

Pennant ants (Andersen 2002) (Generic common name)

Synonyms (WWW5, Bolton 1980) 

Tetramorium grassi Emery, Tetramorium grassii var. laevigatum Mayr, Tetramorium grassii var. simulans Santschi, Tetramorium grazsii [sic] var. mayri Emery, Tetramorium joffrei Forel, Tetramorium joffrei var. algoa Arnold


Tetramorium is a large genus, with 445 known species and subspecies worldwide (Shattuck 1999). Shattuck lists 24 described Australian species, the majority of which are endemic. New Zealand has two established introduced species, Tetramorium bicarinatum and T. grassii, the latter of South African origin. It is first recorded in the literature, with reference to New Zealand, by Brown (1958a). He refers to a series taken at Panmure, Auckland, and another from Remuera. According to Taylor (1961) the former was collected in 1941.


T. grassii is far more prevalent than T. bicarinatum, based on collection records. Nevertheless, its distribution is still somewhat restricted to northern areas of the country, presumably dictated in large part by climate. Specimens have been collected in Northland, Auckland, Coromandel, Bay of Plenty, Waikato, Hawke's Bay, and a single collection from Nelson in 2002; most are from outdoors.

General Description


The antennae of the workers are 11 or 12-segmented, with a 3-segmented club. The lateral portions of the clypeus are raised into a sharp ridge in front of the antennal insertions. The propodeum is armed with a pair of spines above, and a pair of flanges below near the insertion of the petiole (waist). Usually sculptured over head and mesosoma. The tip of the sting has a triangular to pennant-shaped extension projecting upward from the shaft (visible only when the sting is extended).

Diagnostic features of the worker

Length 3.0 to 4.1 mm; antennae 12-segmented; metanotal groove impressed in larger individuals, but may be feeble or absent in smaller ones; sculpture on head and mesosoma; petiolar (front) lobe high and narrow; colour uniformly brown. T. grassii and T. bicarinatum can be distinguished most easily on the basis of the shape of the petiolar node, location of sculpture and colour.


As with T. bicarinatum, little is known of the biology of T. grassii . Taylor (1961) describes the nests as "usually shallow excavations beneath a stone or log, and the ants may utilise bubble cavities or crevices in covering stones for brood storage areas." The reference to 'bubble cavities or crevices' relates to stones of volcanic origin in Auckland City. Food remains in the nests comprised fragments of insects and other arthropods.

Taylor (1961) noted a clear preference of T. grassii for dry, sheltered sunny nesting sites on north facing slopes of several of Auckland's volcanic cones. This is further evidence of the influence of climate, particularly temperature, on the distribution of this species.

Pest Status

Attracted to a wide variety of baits and common in urban areas, so has the potential to be a minor garden nuisance.