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Monarch Butterfly New Zealand Trust secretary Jacqui Knight said not many flowers offered nectar at this time of year and the butterflies would have congregated at one of the few plants that suited their needs - up to 100 monarch butterflies gathered as temperatures climbed to 16degC yesterday.
"We believe they leave pheromones behind in certain trees and so they will cluster there and then on beautiful days ... they will come and visit gardens and look for nectar.
"They top up their nectar and then they go back into trees to overwinter," Ms Knight said.