Pheidole rugosula Forel 1902
Big-headed ant (Andersen 2002) (Generic common name)
Synonyms (Berry et al. 1997 )
Pheidole variabilis Mayr, Pheidole variabilis rugosula Forel
Pheidole is among the largest of ant genera. Wilson (2003) estimates the number of its known species as close to 900, with a large number still to be described. Australia has some 53 species and subspecies. Three of these are established in New Zealand, P. megacephala , P. rugosula and P. vigilans . P. rugosula is Australian in origin; it is still listed as P. variabilis rugosula in Australia (Shuttuck 1999; WWW4).
Distribution (see map)
P. rugosula is the most common of the three Pheidole species established here. Like P. megacephala , it is now well established in Auckland City, but by contrast it has been able to extend its range both northward and southward. It has been collected at a number of sites in Northland (RJH pers. obs.; Lester et al. 2003), is present in Waikato, Bay of Plenty, Taranaki, and Hawkes Bay, and has been collected as far south as Nelson and Christchurch.
The workers of Pheidole are dimorphic (major and minor workers). The antennae are 12-segmented with usually a 3-segmented club. In side view the propodeum is depressed below the level of the pronotum and the forward section of the mesonotum, and these two regions are connected by the steeply sloping rear section of the mesonotum. The nest entrance typically has a small mound of soil extracted from the nest.
Diagnostic features of the major worker
Length 3 mm; head massive with the rear (occipital) margin deeply impressed in the middle; rugae (wrinkles in the cuticle) extending from the clypeus almost to the rear margin of the head; propodeal spines (paired) longer than diameter of propodeal spiracle; colour light brown.
Diagnostic features of the minor worker
Length 2 mm; head with rear (occipital) margin shallowly impressed in the middle; head reticulate laterally, with longitudinal rugae and a more or less smooth medial area extending almost to the rear (occipital) margin; propodeal spines (paired) 2-3x diameter of propodeal spiracle; colour light brown.
Berry et al. (1997) provide a key to Pheidole species in New Zealand.
Details of biology are few. Minor workers have been observed foraging on flowers in a garden in Kohimarama, Auckland (AWD pers. obs.), and one minor in a group of minors and majors extracted from a nest in a lawn on the University of Auckland's city campus was observed carrying a springtail (AWD pers. obs.).
Seed harvesting has been observed also. In January 1980, a senior botany student studying Onehunga weed ( Soliva spp.) growing in the University of Auckland campus, noticed minor workers collecting achenes (small, dry, one-seeded fruits) of the plants, placing them around the nest entrances (surrounded by the usual mound of soil) and carrying them into the interior.
Berry et al. (1997) note that "among the label data for this species were several records of P. rugosula attacking mantid oothecae, including those of the native mantid, Orthodera novaezealandiae Colenso."
Can be abundant around urban areas causing a nuisance. Workers are attracted to pet food left out and windfall fruit. It has been sampled in native habitats but its impacts are unknown.
Compiled by Warwick Don & Richard Harris