Living on Lipids
Surviving the Season on Stored Energy

What are"lipids"?

During their 5 months in Mexico, monarchs remain largely inactive. While they do fly out of their colonies on occasion, most of the time they are motionless, hour after hour, day after day, night after night, week after week. The butterflies must live off their stored lipid reserves all winter. They gained this fat while they were caterpillars and during the fall migration. At the end of the overwintering season, there must be energy left for mating activities and the spring migration northward.

The overwintering habitat is perfect for conserving energy: The high mountains are cold enough so the lipids burn slowly--but not so cold that the butterflies freeze.

Eduardo Rendon-Salinas

Biologists Alfonso Alonso-Mejia, Eduardo Rendon-Salinas and Lincoln Brower studied the rate at which butterflies burn their lipid reserves during the overwintering season. Each month, the researchers took samples of butterflies that were resting on the trees. They measured the amount of lipids stored in the butterflies? bodies and watched how it changed, from November until March.

But do the butterflies also need nectar? It?s common to see overwintering butterflies drinking from flowers when visiting the region. So a quick conclusion might be YES, nectar is important. In fact, some people argued that, by thinning the forest, more flowers would grow and their nectar could help the butterflies survive the winter.

A closer look at the flower-visiting butterflies by Alonso and his team lead to a fascinating conclusion: ?Monarchs that visited flowers at the over-wintering sites had highly depleted lipid reserves. It appears that flower-visiting monarchs do not have enough lipid reserves to migrate back to the breeding areas of the southern United States.?

In other words, the monarchs that are visiting flowers for nectar are "running out of gas." They're so low on lipids that they resort to nectar to try to stay alive. In contrast, the monarchs in the clusters still have enough stored lipids.

Journaling Questions

  • Make a graph so you can see how the lipids dropped each month. Compare the lipid mass of butterflies found in clusters to that of butterflies found at flowers. What do you notice?
  • How many milligrams of lipids does the average monarch burn during the overwintering season, from November through March?
  • A monarch tag weighs 10 mg. How many times that weight does the average monarch lose by the end of the overwintering season?

Lipids - any of a group of organic compounds including fats, oils, waxes,
steroids and triglycerides, that are insoluble in water, but soluble in
common organic solvents.

Education Standards