Monarchs in the Oyamel Forest

Monarchs in the Oyamel Forest is an original illustration set in Michoacan Highlands, Mexico. It lies in the tropics, where the climate is subtropical highland — dry winters, mild summers.

Millions of orange-and-black butterflies hang in dense heavy clusters from dark fir branches, with a smaller cloud lifting through one shaft of pale morning light. Tall straight sacred-fir trunks rise from a steep mossy floor, and thin mountain mist reads as flat pale layers.

Why do monarch butterflies cluster this densely to overwinter?

Butterflies overwinter in clusters this dense to conserve heat, which only works in a narrow band of temperature — cool enough to slow their metabolism, never cold enough to kill them. That band exists at high elevation in the subtropics, on a handful of mountains, in one particular species of fir. The mist is orographic: moist air lifted and cooled by the slope.

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