Sylvain Cordier / Monarch butterfly (Danaus plexippus) wintering in Oyamel pine forests (Abies religiosa) Monarch Butterfly Biosphere Reserve / Reserva de Biosfera de la Mariposa Monarca UNESCO World Heritage Site, An...

Sylvain Cordier / Monarch butterfly (Danaus plexippus), wintering from November to March in Oyamel pine forests (Abies religiosa) Monarch Butterfly Biosphere Reserve, Mexico.

Ingo Arndt / Monarch butterflies (Danaus plexippus) gathered to drink, overwintering colony, Michoacan, Mexico

Ingo Arndt / Cloud of Monarch butterflies (Danaus plexippus) flying, overwintering colony, Michoacan, Mexico

Ingo Arndt / Monarch butterflies (Danaus plexippus) flying amongst trees, overwintering colony, Michoacan, Mexico

Ingo Arndt / Monarch butterfly (Danaus plexippus) hanging from a blade of grass, silhouetted against the full moon, East coast USA.

Ingo Arndt / Monarch butterflies (Danaus plexippus) flying in warmth of midday sun, overwintering colony in Michoacan, Mexico

Ingo Arndt / Monarch butterflies (Danaus plexippus) drinking from pool of water, overwintering colony, Michoacan, Mexico

Ingo Arndt / Male Monarch butterfly (Danaus plexippus) feeding on nectar of Goldenrod flowers, East coast, USA

Floris van Breugel / Monarch butterflies (Danaus plexippus) over winter on Eucalyptus and Monterey Cypress trees near Pismo Beach, San Luis, California, USA December.. When temperatures warm up enough, they will embark on...

Claudio Contreras / Monarch butterfly (Danaus plexippus) hibernating, Mariposa Monarca Special Biosphere Reserve, central Mexico, January.

Claudio Contreras / Monarch butterfly (Danaus plexippus) hibernating, Mariposa Monarca Special Biosphere Reserve, central Mexico, January.