Described by William M. Mann in 1921, the species is endemic to Fiji.

[1] Philidris nagasau makes its living by planting seeds of epiphytes such as Squamellaria in the bark of host trees and tending them like a garden.

Their planting habits share a remarkable similarity to that of humans.

They are able to identify the seeds of their preferred plant, plant these seeds, guard their plots from potential predators, and finally use their own feces to fertilize the young seedling.

This suggests that P. nagasau selectively breed Squamellaria with wider openings that eventually developed into domatia.