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

Claudio Contreras / Hibernating Monarch butterflies (Danaus plexippus) El Rosario Colony, Monarch Butterfly Sanctuary, Mexico, February

Ingo Arndt / Monarch (Danaus plexippus) butterflies in trees, El Rosario, Michoacan, Mexico

Thomas Mangelsen / Monarch (Danaus plexippus) butterfly mass at wintering grounds, El Rosario Monarch Butterfly Sanctuary, Mexico

Tui De Roy / Monarch butterflies (Danaus plexippus) resting on trees in wintering grounds in the mountains of central Mexico, El Rosario Butterfly Sanctuary, Michoacan, Mexico.

Tui De Roy / Monarch butterflies (Danaus plexippus) covering Fir trees on wintering grounds in the mountains of central Mexico, El Rosario Butterfly Sanctuary, Michoacan, Mexico.

Patricio Robles Gil / Monarch butterfly (Danaus plexippus) group, silhoutted some flying and some resting in oyamel trees, Reserve el Rosario Sanctuary, Mexico.

Patricio Robles Gil / Monarch butterfly (Danaus plexippus) some flying and some resting in oyamel trees, El Rosario Sanctuary Reserve, Mexico.

Patricio Robles Gil / Monarch butterflies (Danaus plexippus) in flight, El Rosario Sanctuary, Mexico, November.

Patricio Robles Gil / Mural of the mountain ecosystem of Monarch butterfly reserve at El Rosario Sanctuary Biodiversity, Mexico.