A Monarch butterfly caterpillar feeding on the leaves of a milkweed plant. Photographed at the Grapevine Botanical Gardens. Photo © TexasEagle/Flickr through a Creative Commons license, via TNC

We’ve covered monarch butterflies plenty of times in the past, whether it was reporting survey results showing that many households in the US would pay to help create habitat for the species, showcasing a citizen science project by the Xerces Society to count the winged invertebrates during their migration, or simply highlighting the needs of the orange butterfly in general and how to become involved. Now, given increased media coverage of the Monarch, the Cool Green Science blog for The Nature Conservancy is summarizing hazards and helpers of the species:

Twenty years ago, monarch butterflies occupied so much area in Mexico during the winter you could see it from space. It totaled about 20 hectares, or almost 50 acres, with millions if not billions of butterflies clinging to trunks and branches of trees.

Today, that area is around 4 hectares. The previous year had 1.1 hectares, says Brice Semmens, Assistant Professor at the Scripps Institution of Oceanography at the University of California San Diego.

Semmens was the lead author on “Quasi-extinction risk and population targets for the Eastern, migratory population of monarch butterflies” published recently in the journal Scientific Reports. It is one paper in a long line of sobering butterfly news.

The monarch likely won’t ever become extinct, Semmens says. Small populations live scattered throughout Mexico, the central U.S. and Canada, and some were moved to places as far away as Hawaii and New Zealand.

But the massive eastern migrations between central Mexico and Canada that have inspired people for centuries could be lost.

Semmens’ paper used expert opinion to determine how little occupied winter habitat in Mexico would be needed to sustain a viable migratory population – and at what point it simply may not bounce back.

The authors used estimates of extinction rates with various overwintering sizes, and conclude monarchs need about 6 hectares, or about 15 acres, to cut the risk in half.

But in order to understand how to boost overwintering numbers, people must first understand what hazards the eastern monarch faces.

Semmens and University of Minnesota monarch expert Karen Oberhauser recently walked the Cool Green Science Blog through each threat, as well as some possible solutions.

Check out those threats and solutions in Christine Peterson’s original blog post, here. And to learn more, visit The Monarch Joint Venture webpage.