Cascading Behavior

The most spectacular behavior occurring late in February and in March is "cascading." Literally tens of thousand of butterflies suddenly push off their perches, en masse, and fall downwards. After a fall of 3-5 meters they begin to fly, all in the same direction.

The phenomena is absolutely awesome. Butterflies fill the sky at all levels for a period of up to several minutes. Gradually they fly out of the area or land in nearby foliage--with only green spots on the branches where the tens of thousands of butterflies had recently been. Sometimes one cascade will trigger another, resulting in a sequential cascading from numerous branches in the colony.

The cause and purpose of this spectacular behavior remains a mystery.

There are times during the over-wintering period that bird predators can trigger a cascade in a butterfly colony. But the phenomena we witness in March is orders of magnitude greater than any cascading associated with the presence of birds.

The local people believe it is the noise made by people observing the butterflies that causes cascading. However, no one has shown that monarchs can "hear" airborne sound waves. Monarchs do seem to cascade in response to the presence of people, and this is of concern.

For the first time last week (Feb. 18, 2003), I noticed that most of the cascading (but not all of it) occurred during cloudy periods. In the past, I don’t recall having noted any correlation with clouds or sun. But maybe that’s just because I never noticed it before. I’ll certainly be paying attention from now on.

Nevertheless, the cause is still a mystery. We saw no birds in the colony, and we humans were located far from the site of the cascading. I don’t know, it must just be some sort of manifestation of colony break up. It just can’t be related to anything else. And why it occurs during cloudy weather, I just don’t know.

Journaling Questions

  • Other than sound or sight, can you think of another way the monarchs might be able to sense the presence of people?
  • What experiment could you design to try to tease out the cause of cascading?

National Science Education Standards

Science as Inquiry
Ask a question about objects, organisms, events. (K-4)

Identify questions that can be answered through scientific investigations. (5-8)

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)

History and Nature of Science
Although men and women using scientific inquiry have learned much about the objects, events, and phenomena in nature, much more remains to be understood. Science will never be finished. (K-4)