Polyrhachis yorkana

An arboreal species with all colonies observed occupying polydomous silk nests built between the leaves of lowland rainforest trees.

Identification
Kohout (2006): Polyrhachis yorkana is somewhat similar to Polyrhachis debilis from New Guinea, with both displaying considerable variability in the development of the propodeal spines which range from inconspicuous tuberculae to short spines. However, they differ in numerous characters, including the shape of the head, which in P. debilis is as wide or even wider than long (CI 100-103), while in P. yorkana it is distinctly longer than wide (CI 96-98). In full face view, the eyes of P. debilis do not reach the sides of the head, while in P. yorkana they clearly break the cephalic outline. In lateral view, the pronotum is distinctly convex in P. debilis and rather ﬂat in P. yorkana. In dorsal view, the pronotum in P. debilis is relatively narrow with evenly rounded shoulders, while in P. yorkana the pronotum is distinctly widest just behind the shoulders and, in the majority of specimens examined, the pronotal humeri are subangular or distinctly angular. They also differ in their relative size, with P. debilis distinctly smaller (HL 1.34-1.47 verus HL 1.56-1.62).

Distribution
Polyrhachis yorkana is largely conﬁned to the Wet Tropics of north Queensland, but it has occasionally been collected further north on Cape York Peninsula (Kohout 2006).

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Nomenclature

 *  yorkana. Polyrhachis (Cyrtomyrma) rastellata var. yorkana Forel, 1915b: 110 (w.) AUSTRALIA. Raised to species: Kohout & Taylor, 1990: 521. See also: Kohout, 2006b: 105.

Worker
L: 4, 9-5, 6 mm. Unterscheidet sich von der Rasse laevior Rog. durch den vollstandigen Mangel der Dornen am Epinotum. Die mittleren Dornen der Schuppe sind kurzer als beim Arttypus und der Kopf hinten breiter; sonst gliech.

Type Material
Syntype workers, , , and  - as reported by Kohout (2006).

Type Locality Information
QUEENSLAND, Cape York Peninsula, col. E. Mjöberg.

Additional References
Forel, A. 1915. Results of Dr. E. Mjöberg’s Swedish scientific expeditions to Australia, 1910-1913. 2. Ameisen. Arkiv för Zoologi 9(16): 1-119.

Kohout, R. J. 2006. Review of Polyrhachis (Cyrtomyrma) Forel (Hymenoptera: Formicidae: Formicinae) of Australia, Borneo, New Guinea and the Solomon Islands with descriptions of new species. Memoirs of the Queensland Museum. 52:87-146.