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Why Do Monarch Btterflies Shiver?
Observations of Shivering Behavior
Contributed by Dr. Bill Calvert

Shivering is most common when the temperatures are low. But it's possible to even see a monarch shivering during the peak warmth of the day. When butterflies are down on the ground to drink water they would be cooled by the cold water and need to shiver to raise their body temperature for movement.

Shivering butterflies look like you might imagine from your own experiences in cold weather. The butterflies shiver their wings rapidly in an attempt to warm the muscles inside.

At What Temperatures Can Monarchs Fly?
You'll often hear people say the butterflies are trying to get warm enough to fly. But it may be that shivering helps them get warm enough even to crawl off the ground when they are too cold to fly.

Shivering and crawling at 49 degrees F, but not able to fly. How much warmer must it get before it can fly? shiver004
   
  • Monarchs can crawl at temperatures as low as 5 degrees C (41 degrees F).
  • The monarch's flight threshold is about 13 degrees C (55F). (Flight threshold means that this temperature, 13C, is the lowest temperature at which they can fly somewhat.)
  • In order to fly WELL, with lots of control, they need to attain thoracic temperatures in the upper 20s or even 30s--pretty close to the temperatures that warm blooded mammals run.
  • They can manage to get themselves airborne and glide--and occasionally flap with some control--at temperatures much lower than that, but they cannot fly well at temperatures in the teens.

Keep in mind that the temperature can sometimes drop to zero C or even a few degrees below zero in the sanctuaries. Monarchs are paralyzed by temperatures this cold!

How Long Do Monarchs Stay on the Ground?
I wondered how long a butterfly might be at risk on the ground--whether minutes, hours, half days, a full week. How long would it take one to reach necessary temperatures and move upward?

My impression from observations is that the sunflecks move around the forest each day and probably cover virtually all locations. ("Sunflecks" are small circumscribed areas where solar radiation is entering gaps in the canopy and striking the ground.) So if it is sunny the day after a butterfly is grounded, a sunfleck will find its position sometime during the next day, and warm the butterfly enough to move out of its predicament.

If there is a period of cloudy weather it's a different story, and the risk period could be much longer. If buried by snow, monarchs might stay on the ground under the snow for more than a week. But they are not at much risk buried under the snow, except perhaps by being stepped on.

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Monarchs in 1999 Snowstorm
Snow doesn't always kill monarchs. They can remain alive for days trapped or buried in snow.

National Science Education Standards

  • The behavior of individual organisms is influenced by internal cues (such as hunger) and by external cues (such as a change in the environment).
  • An organism's behavior patterns are related to the nature of that organism's environment.
  • All organisms must be able to obtain and use resources, grow, reproduce, and maintain stable internal conditions in a constantly changing external environment.
  • Regulation of an organism's internal environment involves sensing the internal environment and changing physiological activities to keep conditions within range required to survive.

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