Worm Moon

March's Worm Moon is most commonly explained by the appearance of earthworm casts — the small coiled piles of soil worms leave on the surface — as the ground thaws enough in early spring for them to become active again near the surface after winter dormancy. This is the explanation the Old Farmer's Almanac has published for decades under its Algonquin-attributed list.

A competing and, some researchers argue, more historically grounded explanation ties the name instead to beetle larvae (sometimes called "grubworms") that emerge from the thawing bark of trees at the same time of year, rather than earthworms specifically. Early almanac compilers may have conflated the two, and it's genuinely unclear from the surviving record which insect the original naming tradition referred to — an honest case of sources disagreeing rather than one being simply wrong.

Other regional names sidestep the worm question entirely. Crow Moon, recorded in some Ojibwe traditions, marks the return of cawing crows as a signal that winter is ending. Sap Moon refers to the maple sugaring season, when sap begins running in late-winter thaws and early settlers and Indigenous communities alike tapped trees. Lenten Moon is a Christian-calendar name tied to the Lenten season, which usually overlaps March.

March also carries genuine astronomical significance independent of any full-moon name: the spring equinox falls in this month (around March 20), the point where day and night are close to equal length and the Sun crosses the celestial equator heading north for the Northern Hemisphere's spring.

Maple sugaring, the real activity behind the Sap Moon name, depends on a specific weather pattern — freezing nights followed by thawing days — that triggers sap flow in sugar maples; this window genuinely does cluster around late winter into early spring across the maple's native range in the northeastern US and eastern Canada, making Sap Moon one of the more mechanically explainable alternate names on the list, distinct from the disputed worm-versus-larvae question.

Earthworms themselves aren't native to much of northern North America — many common species were introduced by European settlers and are now considered, somewhat surprisingly, an invasive presence in some northern forest ecosystems, where they can alter soil composition in ways that affect native plant communities. That complicates the earthworm-casts explanation slightly, since the worms this name may reference weren't necessarily part of the pre-contact ecological picture in every region the naming tradition covers.

The Lenten Moon name ties to the Christian liturgical calendar's Lent season, which itself is calculated relative to Easter and therefore, indirectly, to another full moon (the Paschal Moon) — meaning two of this site's monthly full-moon names, March's and April's, both carry genuine Christian-calendar connections layered on top of their more commonly cited folk explanations.

Beetle larvae emerging from thawing bark, the competing explanation for this name, would have been an equally visible early-spring sign to anyone splitting firewood or clearing deadfall — a plausible alternative source for the same general observation earthworm casts are more commonly credited with today.

Robins, often associated with earthworm-hunting behavior in popular imagination, do genuinely return to much of their northern range around this same general time of year, adding another loosely-related seasonal marker to this month.

Frost depth in the soil itself varies significantly by region even at the same latitude, depending on snow cover (which insulates the ground) and local soil composition.

Ground temperature, not just air temperature, ultimately determines when soil-dwelling organisms become active again each spring, regardless of which explanation for this name you find more convincing.