Poecilomyrma

Sarnat and Economo (2012) - Mann named P. senirewae and its subspecies P. myrmecodiae both from the Nadarivatu area. The type series of P. senirewae is actually a mix of both species, and Mann incorrectly believed that the black-headed specimens were minor workers and the red-headed specimens were major workers. He explains that the series was taken from, “a small colony nesting in a hollow twig of a recently felled kauri tree, and a couple of individuals found on leaves.” The type series of P. myrmecodiae was taken from a Myrmecodia ant plant. The confusion Mann experienced with these ants is quite understandable, as additional collections have only contributed to the vexing question of where species boundaries lie. Mann’s prediction that these ants might be “widely distributed though locally hard to find,” has been borne out during the recent survey. Both the geographical and morphological range of this genus was significantly expanded. Poecilomyrma is now known from all seven of the largest islands (only males known from Koro), but records remain quite rare.

Identification
Sarnat and Economo (2012) - Fiji. Head shape ovoid to rectangular. Antenna 12-segmented. Antennal club 3-segmented. Antennal scrobes absent. Anterior clypeal margin variously shaped, but never armed with three broad and blunt teeth. Sides of head lacking carinate ridge extending below eye-level from mandibular insertions to posterolateral head margin. Mandibles triangular; lacking a distinct basal tooth. Mesosoma evenly convex; lacking depression separating promesonotum from propodeum; erect hairs present. Propodeum armed with spines or teeth. Propodeal lobes longer than propodeal spines. Propodeal spines distinctly longer than diameter of propodeal spiracle. Waist 2-segmented. Petiole pedunculate; lacking large anteroventral subpetiolar process.

This sole endemic ant genus of Fiji is also one of the most beautiful ants found on the islands, with a deeply grooved and very shiny integument, reduced propodeal spines, extended and spinose propodeal lobes, a long slender petiole and often striking red and black coloration.

Distribution
Poecilomyrma is the only ant genus that is strictly endemic to the Fijian archipelago.

Nomenclature

 *  POECILOMYRMA [Myrmicinae: Formicoxenini]
 * Poecilomyrma Mann, 1921: 445. Type-species: Poecilomyrma senirewae, by original designation.

Sarnat and Economo (2012) - The morphological variation encountered in Poecilomyrma is very difficult to organize into any geographical or phylogenetic pattern, and even after an earnest study it is to some degree arbitrary as to whether the genus is split into seven species or lumped into one. To begin with, there are three distinct color morphs. Morphotype #1 (as exemplified by P. senirewae) is all red except for the gaster. Morphotype #2 (as exemplified by Poecilomyrma sp. FJ05) has a black gaster and head, a red mesosoma, and infuscated waist segments. Morphotype #3 is entirely black. The sculpture of the mesosoma varies substantially from uniform parallel carinae to fully reticulated rugae. The cephalic sculpture, postpetiole sculpture and length of propodeal spines and lobes all vary, as well. Size also varies conspicuously. However, the aforementioned characters do not appear to be correlated with each other in any meaningful way. For example, particular sculpture patterns do not tend to correlate with color morphotype or with size or with geography.

Despite the great variance among the series of specimens collected, the variance within any particular series is quite low. That is to say, variation among local populations is quite high while variation within local populations is quite low. Similarly highly structured populations are observed in the Fijian Cerapachys. Both of these genera, in Fiji, have wingless ergatoid queens, which may be a factor in the limited gene flow. The challenges of species delineation would be better met by molecular tools capable of penetrating deeper than this cursory study of surface sculpture and color. The males are occasionally collected by malaise trapping, and they exhibit a number of variable characters as well, especially with regard to overall size, relative eye size, and color.