The Dynamics Of Butterfly Migration

Millions of monarchs descend on the El Rosario butterfly preserve each year.
SYLVAIN CORDIER/GETTY

The Monarch Watch Tagging Program is a large-scale citizen science project that was initiated in 1992 to help understand the dynamics of the monarch's spectacular fall migration through mark and recapture. Each fall researchers give out more than a quarter of a million  tiny stickers marked with an email address, phone number, and unique identification code. Volunteers apply the stickers to the discal cell on butterflies’ wings and record the code and the location. If the tags are ever spotted again, the data help the researchers figure out where the butterflies had been.

Read about some travellers who came across one of these stickers, and helped reconstruct a journey of hundreds and hundreds of miles.