Margaret Campbell, of Oamaru, asks :-
By early winter the Red Admiral butterflies have all gone but Yellow Admirals are here and in the tussock covered hills nearby. Is there a reason for these changes?
Brian Partick, an entomologist at Otago Museum, responded.
All butterflies and moths are seasonal, that is they have a life-cycle that is in tune with their environment and adults are only produced at certain times of the year. Although red and yellow admiral buterflies can sometimes be found flying together and their larvae share some of the same nettle hosts, they have a different seasonal pattern. Red admiral adults are often abundant in October and again in February/March, whereas yellow admirals emerge as adults in December/January then again in April/May. In good years yellow admirals can be very abundant in late autumn.
The best seasons for the admirals are when nettles, their larval host, have flourished in a moist spring and summer. Tree nettle is the favoured larval host for the red admiral, while yellows thrive on introduced nettles around farm shelterbelts and in suburban gardens.
Interestingly the red admiral is only found in New Zealand (endemic), whereas the yellow admiral, although first described from New Zealand, is naturally shared with Australia. Our third admiral is endemic to the Chatham Islands and resembles the red admiral. It is important that we nurture these beautiful admirals by leaving a patch of nettles in our gardens. It is wonderful to observe the whole life-cycle and miracle of metamorphosis.