March Full Moon: How the Full Worm Moon Got Its Earthly Name

It's the time of the season.

The full worm moon will crawl around the planet on Thursday night. The annual worm moon is always the first full moon in March and the last full moon before the Spring Equinox.

Despite the label, the moon bears no resemblance to any slimy annelids. In fact, the full worm moon is so named because it coincides with the seasonal resurgence of earthworms.

In cold climates in the winter, the soil becomes inhospitable for most earthworms. The groundwater in the soil freezes, and kills any unfortunate worm without a survivalist instinct. For some species of earthworms, the cold is an unassailable death sentence. These worms lay eggs in insulated sacks that protect their offspring from the harsh weather. Then, completing their true parental sacrifice, they promptly freeze to death.

More resilient worms burrow into the ground, where they are protected from the winter chill. These worms wriggle beneath the frost line, far enough underground that the water in the soil remains liquid even during the cold season. They take advantage of warm days during the winter to navigate through the soil in search of food, and spend the rest of their time idly waiting for the return of sunny days whilst several feet below the surface.

After months of either gestation or waiting for warmer weather, the earthworms erupt from the soil around the time of the full worm moon. With their food source emerging from the ground, birds begin to migrate back to the north, portending the start of spring.

The resurrection of the worms also signals that the planting season is nigh, making the full worm moon an important milestone for farmers. Native Americans, who tracked the seasons with lunar cycles, noticed the importance of the March full moon and named it for the earthworm. The name was then appropriated by Colonial Americans.

So when you’re looking up at the full worm moon Thursday night, cast your eyes downward too; you might catch a glance of its namesake.

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