Did You Notice?

Observation: Thousands of monarch butterflies are on the ground. They are under two large trees. The edges of the picture look dark. However, a ray of sunlight is striking the center of the picture.

Interpretation: There has been a storm. The monarchs fell down from the large trees, due to wind or rain. Temperatures have been cool, below 41 degrees F. Some butterflies are able to move now, probably because they are basking in the sunlight to warm their muscles.

Evidence to back up this interpretation: Monarchs are normally in the branches or on the trunks of oyamel ("oi-ya-mel") trees. When they fall, monarchs always move off the forest floor as quickly as they can. However, if they are too cold, it can take hours or days for them to climb back into the safety of the trees. This is because monarchs are paralyzed by cold temperatures. They can't even crawl unless their muscles are 41 degrees. Monarchs can warm their muscles by basking in sunlight. "Sometimes they have to wait until a tiny speck of sunlight reaches the forest floor," says Dr. Bill Calvert.

About this picture: This picture was taken during the large storm in the winter of 2002, so this is an unusually large number of fallen butterflies!