Rhytidoponera chalybaea Emery 1901

Compiled by Warwick Don & Richard Harris 2005

Biostatus: Introduced

Classification

Family:	Formicidae
Subfamily:	Ectatomminae
Tribe:	Melophorini
Genus:	Rhytidoponera
Species:	chalybaea

Common name(s)

Blue pony ants (for impressa species group - Andersen 2002)

Synonyms (WWW5)

Ectatomma (Rhytidoponera) cyrus Forel, Rhytidoponera impressa var. chalybaea Emery

Origin

Rhytidoponera is a large genus with 104 described species, 76 of which occur in Australia (Shattuck 1999). One species is definitely established in New Zealand, R. chalybaea , a recent arrival from Australia. Intercepted on several occasions (associated with imported poles and sawn timber), this species probably became established here during the 1950s. A second species, R. metallica , is probably established, with several recent collections (2001 and 2003) in Napier.

Distribution

R. chalybaea has become established in Northland, Auckland (where it is particularly numerous), and Bay of Plenty. A continued presence in Hawke's Bay and Taranaki requires confirmation.

General Description

Identification

The genus Rhytidoponera is distinguished by means of a tooth on the leading edge of the pronotum, pointing downward just above the front legs. The node of the petiole has distinct front, top and rear faces. The tips of the tibiae of the hind legs each have either a single small, simple comb-like spur, or two spurs, one large and comb-like and one small and simple.

Diagnostic features of the worker

Length about 6.8 mm; a member of the impressa species group (Ward 1980) characterized by a distinctive saddle-shaped constriction of the upper surface of the mesosoma; the profile of the posterior part of the subpetiolar spine is a smooth curve, running at an acute angle - so the broad base is barely noticeable (P. Holder, NPPRL); colour of body with a slightly metallic blue appearance - some workers may be brown on sides of body (cf. R. metallica which has a metallic green appearance), legs and antennae rusty red-brown.

[Rhytidoponera chalybaea] head. Image: April Nobile (Specimen code: CASENT0172343). www.antweb.org Image — Rhytidoponera chalybaea head. Image: April Nobile (Specimen code: CASENT0172343). www.antweb.org

Rhytidoponera chalybaea profile. Image: April Nobile (Specimen code: CASENT0172343). www.antweb.org

[Rhytidoponera chalybaea] dorsal view. Image: April Nobile (Specimen code: CASENT0172343). www.antweb.org Image — Rhytidoponera chalybaea dorsal view. Image: April Nobile (Specimen code: CASENT0172343). www.antweb.org

Biology

Nests in Australia are usually located in rotten logs or wood fragments, but may be found in the soil under stones (Taylor 1961). Colonies usually comprise fewer than 250 workers. Like the many Rhytidoponera species in Australia, which exploit human-disturbed habitats, R. chalybaea is found in urban areas in this country, nesting under footpaths, stones and in gardens. Several workers have been collected while foraging on footpaths in Auckland. Unlike most species in the genus, R. chalybaea possesses winged queens which, after fertilization, become wingless (dealate) and found new nests in the usual way.

Pest Status

A large species by New Zealand ant standards. As a consequence can cause concern when discovered in urban situations. Possesses a powerful sting.