Polyrhachis gravis species-group

The Polyrhachis gravis species-group is comprised of species in the subgenus Campomyrma.

Species

• Polyrhachis bispinosa
• Polyrhachis capillata
• Polyrhachis captiva
• Polyrhachis curtospinosa
• Polyrhachis gravis
• Polyrhachis hespera
• Polyrhachis opacita
• Polyrhachis palmerae
• Polyrhachis pseudothrinax
• Polyrhachis unicornis

Identification

• Key to Polyrhachis gravis species-group workers

Distribution and biology

Species of the P. gravis-group are distributed primarily throughout the arid and monsoonal zones of central and northern Australia. Most are relatively rare and only occasionally collected in poorly known and isolated parts of the country. From a few known records, they are terrestrial nesters, building their nests under the ground with entrances covered by a rock, piece of wood, or simply concealed by a tuft of grass.

Diagnosis

Worker

Medium-sized to relatively large ants (HL > 2.30) with general characteristics of the genus and subgenus. Mandibles with 5 or 6 teeth; anterior clypeal margin widely truncate medially, with truncate portion mostly irregularly denticulate. Head with sides in front of eyes rounded towards mandibular bases; behind eyes sides with short, postocular lateral ridges, forming distinct, narrowly rounded occipital corners, before converging into relatively narrow occipital margin. Eyes mostly moderately large (except in P. hespera) and convex; ocelli lacking. Pronotal humeri angular (as in P. capillata or P. opacita), or narrowly rounded with pronotal lateral margins behind more-or-less emarginate (as in P. curtospinosa, P. palmerae or P. unicornis). Mesonotal and propodeal dorsa strongly converging posteriorly with lateral margins of propodeal dorsum terminating in short, upturned teeth. Petiole scale-like, with four spines or teeth of various configurations, or with a pair of dorsal spines and lateral teeth greatly reduced (as in P. bispinosa), or with a single dorsal spine and two lateral teeth (as in P. pseudothrinax and P. unicornis.) Gaster in side view with anterior face straight; dorsoanterior margin first gastral tergite with a distinct carina in most species, except P. captiva and P. opacita, where carina is only poorly indicated.

Queen

Apart from sexual characters, including the ocelli, complete thoracic structure and wings, very similar to worker. Armament of pronotum, propodeum and petiole distinctly reduced with spines and teeth shorter and stouter. Sculpturation, pilosity and colour virtually identical to worker. The only known queen is that of P. pseudothrinax described below.

Related Pages

• Campomyrma
• Polyrhachis

References

• Kohout, R.J. 2013. A review of the Polyrhachis gravis and micans species-groups of the subgenus Campomyrma Wheeler (Hymenoptera: Formicidae: Formicinae). Memoirs of the Queensland Museum, Nature 56, 92-117.