This winter, whenever the Fahrenheit scale tops 50 degrees, I try to spend some time in the garden. What could I possibly have to do at this time of year? Well, it allows the chickens to get outside of their 32 square foot pen while I am around to watch for Mr. or Mrs. Hawk, and it allows me to work on expanding the garden. I am planning for a grand affair this summer – with my garden – so I am adding garden beds, expanding my growing space from 128 square feet to 620 square feet (so far).
Last Saturday, even though it only got to 41°F, it was sunny, and I decided to get some garden preparations done. I was turning over some soil in order to level an uneven path that has annoyed me for years. Of course, the chickens came over to investigate and quickly discovered the juicy worms that were being disturbed. So, we had to dig together. Or rather, I had to dig very slowly to avoid accidently pinching a chicken foot! It was charming though. I was in no rush, and I wondered how quickly those worms would transform into healthy omega-3 fats in my eggs.
Whenever I see an earthworm, I am reminded of a National Geographic article (see below) on earthworms and how they are not native to the North American continent. This news surprised me when I first read it years ago. Many ecologists scorn non-native species, or at least invasive species, and so I had to grapple with my feelings about this information. My earliest memory of earthworms is collecting them in the third grade playground for our science class’ terrarium. I was the only girl who would pick up the earthworms, a feat that made me suddenly – if only temporarily – the cool kid, instead of the quiet, shy kid that I was. Since then, I’ve come to not only like worms, but to value their ability to break up my clay soils and to help transform the materials I add to my lasagna-style garden beds into soil. Am I to now doubt their “right” to be here? Are they causing ecological chaos?
My earthworm knowledge is limited. I know they are hermaphrodites, yet two individuals are needed to transfer sperm. I know they have several hearts. I know they are sensitive to light. I know that you can buy earthworms to have an indoor compost bin, or worm castings to augment your soil. Recently, I’ve seen catalogs that sell worm cocoons – earthworms lay cocoons after mating, from which one to five small worms emerge. These cocoons are on my “To Observe” list now. I shall have to look purposefully because they are smaller than a grain of rice.
What about being non-native? I reread the National Geographic article I mentioned above. I also found it online if you’re interested: http://ngm.nationalgeographic.com/2007/05/jamestown/charles-mann-text/1
It is long, but quite good. My memory was wrong in the extent of this invasive status of earthworms. Earthworms were non-existent before, or wiped out by, the last ice age, over 10,000 years ago. This means any areas north of the southern boundary of the ice sheet evolved since the last ice age without the help or impact of earthworms. That is until the Europeans introduced them. It is hypothesized that worms were in the ballast of ships arriving to the New World to load up on tobacco and other colonial exports, and have very slowly made their way to the northeastern United States and into Canada. Since Virginia is south of the last ice age boundary, we have native earthworms, along with the introduced earthworms.
What harm could these little garden allies do? We can think of the forest ecosystem as a unit, much like any one individual is a system of parts. The leaf litter, which should be several inches thick, is akin to an organ, a skin barrier that holds in moisture, prevents soil erosion, and supplies nutrients, among other functions. Earthworms introduced from Europe break down this leaf litter layer too quickly, and change the forest floor ecosystem. Ecologists have been studying the effects of the earthworm’s actions. Observed changes include alterations in the nitrogen cycle, conversions of soils from acidic to more neutral pH (most healthy forests thrive in soils with a pH between 4 and 6), and disruption to native wildflower roots. With a reduced herbaceous layer, there is a resultant reduction in insect pollinators. It appears the little fellows are quite industrious and can accomplish quite a lot, showing how an introduced species can quickly alter ecological systems that evolved over long time periods.
I would love to have a northern forest ecosystem in which to wander. They are lovely spaces. Instead, I have Halcyon and my garden, spaces I love dearly. I want any help I can get with my soil, which has been compacted by years of dairy farming. All earthworms are welcome. I know I am changing the land with my actions, just as the colonists did and the Native Americans before them. Hopefully, I will do so kindly.
This earthworm research has left me with more questions. I will close with one: Why do earthworms come to the surface when birds drum or create vibrations? Evolution should select for worms that do not come to the surface, causing this behavior to largely disappear because the earthworms that survive a “vibration episode” would be the cautious ones, and they would produce cautious offspring. So I speculated that rain must also cause vibrations, and that earthworms were better off risking being a possible meal than drowning. I am wrong. Apparently earthworms do not get flooded out of their homes, but emerge on purpose to more easily migrate to new spaces. So why do they answer the call of the hungry bird?