Woolly Bears, Berry Crops and Fog: What Winter Folklore Really Predicts

As days shorten across the Northern Hemisphere, a familiar set of autumn sightings resurfaces in conversation: a fuzzy caterpillar crossing a path, a tree heavy with bright red berries, thick fog hanging over a field in August. Folklore passed down for generations claims each of these is a sign that a hard winter is on its way. Wildlife and conservation bodies that have studied these claims say the signs are real observations, but their meaning as forecasts does not hold up.

The woolly bear caterpillar myth

The best-known example in North America is the woolly bear caterpillar, the larval form of the Isabella tiger moth. Folklore holds that the width of its reddish-brown middle band predicts the severity of the coming winter: a narrow band means a harsh winter, a wide band a mild one. According to the US National Weather Service, the belief dates back to colonial times and holds that the amount of black on a woolly bear in autumn varies in proportion to how severe the coming winter will be.

The agency says the band width actually reflects the caterpillar's own growth history, not the weather ahead. The caterpillar molts six times, and with each molt it becomes less black and more reddish, according to the National Weather Service. Caterpillars that had a better growing season tend to be larger with wider orange-brown bands, while younger or late-season caterpillars show more black. There are roughly 260 tiger moth species in North America, each with its own coloring pattern, which adds further variation unrelated to winter severity.

Berry crops, acorns and other 'abundance' signs

A folk belief holds that trees heavy with berries, or an unusually abundant acorn crop gathered by squirrels, are signs that nature is stocking up food supplies before a difficult season. A list of 20 traditional winter signs compiled by the Farmers' Almanac from Cleveland-based weather observer Dick Goddard includes a heavy acorn crop among the signs said to point to a hard winter.

The Woodland Trust's Nature's Calendar project, which tracks fruiting times across the UK, attributes fruit abundance to the growing conditions of the preceding months rather than to what is coming next. A warm, dry spring provides more time for pollination and tends to produce higher fruit scores, the project notes, while late frosts or unseasonable heatwaves can reduce the crop. Fruit abundance is tracked mainly as an indicator of food availability for wildlife over winter, not as a weather forecast.

Other traditional signs from the Farmers' Almanac list

The same Farmers' Almanac compilation lists dozens of other folk signs still cited today. Among animal-behavior claims: raccoons growing thicker, more banded tails; geese, ducks and snowy owls migrating or arriving earlier than usual; bees sealing themselves into hives sooner; mice trying harder to get indoors; and ants marching in disciplined lines rather than scattering.

Plant- and insect-based signs include thicker-than-normal skins on onions and husks on corn, hornets building nests higher in trees, and spiders spinning unusually large webs. One widely repeated rule involves slicing open a ripe persimmon seed: a spoon-shaped kernel is said to predict heavy, wet snow, a fork shape a mild winter, and a knife shape a bitter, cutting cold. Another tradition holds that counting the number of foggy days in August predicts the number of snowstorms in the following winter.

Why the signs persist

None of the sources reviewed found a scientific mechanism linking any of these signs to future winter severity. Instead, each sign tracks something that already happened: a caterpillar's growing season, a plant's spring pollination, or a squirrel's response to the current nut crop. Because these natural events happen before winter arrives, they can look like a preview of the season even when they are simply a record of the season just finished.