Southern blue butterfly (Zizina labradus oxleyi)
Species: Z. labradus
Sub species: Z. l. oxleyi
Scientific name: Zizina labradus oxleyi
Common name: Southern blue butterfly
Zizina labradus oxleyi is native New Zealand subspecies of the butterfly Zizina labradus which is an Australian species that has colonized NZ and hybridized the southern blue out of existence through much of the country except in the south east of the South Island.
It has a wingspan of about 20mm and is found in grassland, open spaces with gravel or sand. Its caterpillar feeds on small leguminous plants like clover, trefoil, vetch
Below is a link to a page showing the minute physical difference between the male genitalia of Zizina labradus and Zizina labradus oxleyi.. Visible only under a microscope.