I recently was contacted by a reader with a question I invariably get every year, as the weather turns colder: Where do earthworms go in the winter? Similarly, people want to know whether earthworms can survive through winter in their garden beds or compost piles. Its an understandable concern. We gardeners work so hard to create an environment to attract worms and promote their reproduction all through spring and summer. The last thing we want to do is see it all come to an end as the weather turns frosty.
Specifically, the question that prompted me to write this article came from an urban gardener who was raising earthworms in his indoor bin under the sink in his kitchen. His wife had discovered his obsession and relegated the worms to an outside existence. Yet with no real garden in which to go, he was worried that his growing collection of apartment-raised wigglers would meet their maker if his bin was relocated to the frigid outdoors.
This is one of those bad news, good news answers. My reply to this newbie worm farmers inquiry went something like this: No Wally, your worms wont survive winter. I went on to explain that all was not lost though. Although worms cant survive freezing temperatures, they lay eggs that are encased and protected by very small cocoons. They can survive through winter to emerge as tiny baby worms, once temperatures warm up again. The worms Wally was worried about losing would be replaced by a contingency plan, cleverly crafted by none other than Mother Nature herself. Wally would have new worms once the weather warmed.
Worldwide, there are approximately 6,000 earthworm species, while only about 30 are found in the United States. And the most popular of all in the garden are commonly known as red wigglers. Because they live in just the upper layers of soil and among leaf debris, theyre a familiar sight in compost piles and gardens. Yet, because they never burrow far enough into the ground to avoid freezing temperatures, they dont survive those conditions. Fortunately, the eggs laid before their demise provide sufficient replacements next spring.
Other earthworms, such as the common night crawler, can survive winter conditions by burrowing deep into the soil to below the frost line (the level below the soil surface in which groundwater freezes). That distance varies based on different parts of the county, ranging from zero to six feet in the coldest regions. Yet safely below the frost line, they live out the winter in small cavities or chambers. Since night crawlers dont truly hibernate, you may find them reemerging during a period of unseasonably warm weather and returning deep below ground once the weather turns cold again.
Escaping the cold is just part of what allows worms to survive through the winter. The other issue, of course, is in how they breathe. Worms dont have lungs. Instead, they breathe through their skin, as long as it stays moist. To keep their skin moist through winter, they release fluid and mucous that coats their body for whatever time needed.
Under ideal conditions, scientists estimate the average lifespan of earthworms that survive winter at four to eight years while the most common garden varieties live only one or two years. So whatever time our subterranean friends have on this earth, or in it, let us celebrate all they do to improve the conditions of our soil and take comfort in knowing theyll be back to help us in the garden, just about the time we need them most.
Joe Lampl, host of Growing a Greener World on PBS, is a Master Gardener and author. For more information visit www.GrowingAGreenerWorld.com .