The Cloud Effect
Contributed by Dr. Bill Calvert

The "cloud effect" is another beautiful butterfly behavior. This occurs in the colony when the sun goes behind a cloud. It is especially pronounced after a long morning of sunshine, when the sun has heated the forest and the colony. In this picture, taken from a helicopter by Dr. Lincoln Brower, a cloud has just blocked the sun. Basically what occurs is as follows:

When the cloud comes, all the butterflies that were basking immediately push off into the air. The sound of their wings, which is normally a soft din resembling light rain, increases audibly to a noise like a bee hive. The recently airborne butterflies fly around until either one of two things occurs.

1) The sun returns--and the butterflies resume basking in exposed positions as they were before. Or:
2) The cloud remains--and the butterflies abandon their exposed positions and fly back to their clusters in more protected areas of the forest.

The behavior, which is dazzling to witness, is thought to serve an important purpose.

Try This! Journaling Questions
What purpose do you think is served by the behavior known as the "cloud effect"? That is, why do you think the butterflies suddenly fly into the air the moment the sun goes behind a cloud? What are they trying to do?

Students Answering This Challenge Question
Video Clip

National Science Education Standards

Science as Inquiry
Science investigations involve asking and answering a question and comparing that to what scientists already know about the world. (K-4)

Scientists develop explanations using observations (evidence) and what they already know about the world. Good explanations are based on evidence from investigations. (K-4)

Life Science
The behavior of individual organisms is influenced by internal cues (such as hunger) and by external cues (such as a change in the environment). Humans and other organisms have senses that help them detect internal and external cues. (K-4)

Behavior is one kind of response an organism can make to an internal or environmental stimulus. Behavioral response is determined in part by heredity and in part from experience. (5-8)