A pair of common mormon butterflies fly in the air amidst the flowering plants along Singapore's Old Upper Thomson Road on April 30, 2021. (Photo by Then Chih Wey/Xinhua)

A pair of common mormon butterflies fly in the air amidst the flowering plants along Singapore's Old Upper Thomson Road on April 30, 2021. (Photo by Then Chih Wey/Xinhua)

A pair of common mormon butterflies fly in the air amidst the flowering plants along Singapore's Old Upper Thomson Road on April 30, 2021. (Photo by Then Chih Wey/Xinhua)

A pair of common mormon butterflies fly in the air amidst the flowering plants along Singapore's Old Upper Thomson Road on April 30, 2021. (Photo by Then Chih Wey/Xinhua)

A common mormon butterfly is seen amidst the flowering plants along Singapore's Old Upper Thomson Road on April 30, 2021. (Photo by Then Chih Wey/Xinhua)

A pair of common mormon butterflies fly in the air amidst the flowering plants along Singapore's Old Upper Thomson Road on April 30, 2021. (Photo by Then Chih Wey/Xinhua)