Lucas Bustamante / Monarch butterflies (Danaus plexippus) flying during a warm morning. When the overwintering period draws to an end large numbers become active. Michoacan, Mexico, February.

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

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.

Floris van Breugel / Monarch Butterflies (Danaus plexippus) roosting in winter in dense groups, Southern California, USA

Stephen Dalton / Monarch butterfly (Danaus plexippus) female in flight. Did you know? Monarch buttterflies migrate up to 2500 miles from Mexico to Canada.

Inaki Relanzon / Clouds of Monarch butterflies {Danaus plexippus} flying and resting on trees while on migration, Miochacan, Mexico, January 1997

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) drinking from pool of water, overwintering colony, Michoacan, Mexico

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

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

Jack Dykinga / Monarch Butterflies (Danaus plexippus) covering the trunk of a coniferous tree, Sierra Chincua Monarch Butterfly Biosphere Reserve, Michoacan, Mexico, Central America

Rolf Nussbaumer / Monarch butterfly just emerged from chrysalis {Danaus plexippus} Texas, USA.

Jim Brandenburg / Monarch (Danaus plexippus) butterfly group resting on Giant Sunflower (Helianthus giganteus) during migration, Iowa

Jim Brandenburg / Monarch (Danaus plexippus) butterfly newly emerged from chrysalis, California

Ingo Arndt / Monarch (Danaus plexippus) butterfly feeding on nectar of Goldenrod during migration, East Coast, USA

Ingo Arndt / Monarch (Danaus plexippus) butterflies gathering to drink water and take up minerals, Michoacan, Mexico

Patricio Robles Gil / Monarch (Danaus plexippus) butterfly, mass flying in wintering grounds, Monarch butterfly Biosphere Reserve, Michoacan, Mexico

Michael & Patricia Fogden / Monarch (Danaus plexippus) butterfly, feeding on Scarlet Milkweed (Asclepias curassavica) in the cloud forest, Costa Rica

Thomas Mangelsen / Monarch (Danaus plexippus) butterfly group perching on a female tourist, El Rosario Monarch Butterfly Sanctuary, Mexico

Tim Fitzharris / Monarch (Danaus plexippus) butterflies on lupine, Michoacan, Mexico

Jim Brandenburg / Monarch (Danaus plexippus) butterfly, Minnesota

Jim Brandenburg / Monarch (Danaus plexippus) butterfly emerging from cocoon, Minnesota

Jim Brandenburg / Monarch (Danaus plexippus) butterfly group resting on Thickspike Gayfeather (Liatris pycnostachya) flowers, North America

Jan Vermeer / Monarch (Danaus plexippus) branches covered with butterflies, Pacific Grove, California

Edwin Giesbers / Close up of Monarch butterfly (Danaus plexippus) wing detail. Captive.

Bruce Thomson / Monarch butterfly (Danaus plexippus) feeding on thistle (Asteraceae) flower. Introduced butterfly established in temperate and subtropical regions, Bunya Pine Mountains National Park, Queensland, Aust...

Rolf Nussbaumer / Monarch butterfly (Danaus plexippus) caterpillar pupa on Aquatic milkweed (Asclepias perennis). Hill Country, Texas, USA. Sequence 6/6.

Rolf Nussbaumer / Monarch butterfly (Danaus plexippus) caterpillar pupating on Aquatic milkweed (Asclepias perennis). Hill Country, Texas, USA. Sequence 5/6.

Rolf Nussbaumer / Monarch butterfly (Danaus plexippus) caterpillar pupating on Aquatic milkweed (Asclepias perennis). Hill Country, Texas, USA. Sequence 4/6.

Rolf Nussbaumer / Monarch butterfly (Danaus plexippus) caterpillar pupating on Aquatic milkweed (Asclepias perennis). Hill Country, Texas, USA. Sequence 3/6.

Rolf Nussbaumer / Monarch butterfly (Danaus plexippus) caterpillar pupating on Aquatic milkweed (Asclepias perennis). Hill Country, Texas, USA. Sequence 2/6.

Rolf Nussbaumer / Monarch butterfly (Danaus plexippus) caterpillar starting to pupate on Aquatic milkweed (Asclepias perennis). Hill Country, Texas, USA. Sequence 1/6.

Rolf Nussbaumer / Monarch butterfly (Danaus plexippus) caterpillars feeding on Aquatic milkweed (Asclepias perennis). Hill Country, Texas, USA.

Patricio Robles Gil / Monarch butterfly (Danaus plexippus) large groups of butterflies hanging from Oyamel branches, Sierra Chincua Sanctuary, Mexico.

Patricio Robles Gil / Oyamel tree full of Monarch butterflies (Danaus plexippus) in fog, Sierra Chincua Sanctuary, Mexico.

Patricio Robles Gil / Oyamel tree full of Monarch butterflies (Danaus plexippus) in fog, Sierra Chincua Sanctuary, Mexico.