We have the impression that earthworms are beneficial insects that turn the soil, decompose organic matter, and feed plants with their own poop. But is this really the case?
Rules that apply in some areas of the planet don't apply in others, and can even have the opposite result. You may not know that earthworms can disrupt the North American continental ecosystem, and even for human farmland, earthworms are not always beneficial. Today we'll learn more about the earthworm you didn't know.
Over the past 300 years, North America has been quietly and radically transformed. A group of invasive creatures have been snaking and creeping underground, releasing vast amounts of carbon dioxide into the atmosphere while destroying forests. They are the earthworms that we once called beneficial insects. Earthworms are a large group of annelids that live on a diet of soil (organic matter such as rotting leaves). They are usually hermaphroditic, carrying their own sperm and eggs, but require heterologous fertilization.
Sexually mature earthworms also have "secondary sexual characteristics". The sign that an earthworm can mate is the raised circle on the earthworm's body, called the reproductive band. The reproductive band is like a desktop shortcut to the earthworm's ding dong, so if you cut it, you can't reproduce, so earthworms cut into kung pao chicken will not produce more small earthworms. Many people have a positive impression of earthworms, a view that actually comes from Darwin himself.
Darwin studied earthworms at his home in England for 40 years, and he conducted a variety of experiments on earthworms, and in 1881 he published a book on the subject of earthworms: The Formation of Vegetable Mould Through the Action of Worms.
In this book Darwin stated: "It may be doubted whether there are many other animals which have played so important a part in the history of the world as the earthworm. part in the history of the world, as have these lowly organized creatures)." He was half right: earthworms did occupy an important place in the ecosystem, and were often called "ecosystem engineers" by researchers, but their role in the New World was not faithful to Darwin's predictions.
However, Darwin's reputation made the book an instant bestseller, and his attitude toward earthworms spread to human society as a whole. The first thing to acknowledge is that earthworms are indeed important decomposers, but they can also be detrimental to agriculture. For example, the trenches they dig can cause pollution by losing fertilizers and pesticides from farm fields to places they shouldn't go. Secondly, earthworms are capable of turning the soil and aerating the roots of plants, but soil that has been turned by earthworms also becomes more susceptible to erosion and dries out more easily. Annise Dobson, an ecologist at Yale University, describes earthworm-treated soil as "stringy meat" and says that many gardeners believe that earthworm-loosened soil damages plants.
Everyone on earth knows that Darwin was an earthworm controller.
Killing "beneficial insects" in North American forests
Bernie Williams, an earthworm researcher with the Wisconsin Department of Natural Resources, has made similar observations, finding that many residents of the state hate earthworms because they kill vegetables and flowers. She also notes that earthworms sometimes flood out of the foundations of houses like Medusa's hair. More importantly, for North American forests, earthworms are invasive. This is because there are no "native pond" earthworms in North America; in fact, there were no earthworms in North America 10,000 years ago. During the last ice age, when one-third of North America was covered by glaciers, earthworms were emptied out.
Because earthworms have low mobility and defense, the common earthworm (Lumbricus terrestris), now common in North America, is native to Western Europe and was brought to the Americas by 18th century European colonists as fish bait or soil thinning organisms. In fact, the common earthworm is now found on all continents except Antarctica, and Dobson refers to the expansion of the common earthworm as "global worming.
Earthworms affect all aspects of the soil, such as the decomposition of organic matter, carbon storage, surface runoff, and more. Earthworms from the Old World are pushing back the old order of the New World from the roots of the forest. Researchers Melissa McCormick and Dennis Whigham of the Smithsonian Environmental Research Center and Katalin Szlavecz of Johns Hopkins University point out that earthworms are terrible creatures for North American forests.
Fallen leaves and dead branches in a North American forest
Prior to the arrival of earthworms, leaf litter in North American forests was decomposed by microorganisms, nematodes and fungi. However, the decomposition of these organisms is very slow, so the forest topsoil can accumulate very thickly. Earthworms are the equivalent of soil gas pedals, rapidly decomposing organic matter, releasing its nutrients in the form of poop, and changing the pH, density, and other physicochemical properties of the soil dramatically during this "illegal" high-speed decomposition.
Some species of Cypripedioideae
Because North American forests have evolved for tens of thousands of years in the absence of earthworms, native plants cannot quickly adapt to the new substrates that earthworms bring. For example, native North American plants such as extension grass (Trillium tschonoskii Maxim.), ladle orchid (Cypripedioideae), and Canadian dancing crane grass (Maianthemum canadense) are rapidly disappearing because of the arrival of earthworms.
In addition, the thick layer of decaying leaves and other organic matter on the forest surface originally served as a habitat and nursery for many animals and plant seedlings. When the surface organic matter layer is eaten by earthworms, these organisms are directly exposed to the environment and are vulnerable to predators. Josef G rres, a soil scientist at the University of Vermont in the United States, cries foul about earthworms. He says that in the New England region of the U.S. East, where earthworms have invaded, it is now difficult to find even seedlings in the formerly famous maple forests. He believes this may be because the arrival of earthworms has made maple seedlings the only target for herbivores as the rest of the understory disappears.
A is the ash soil of the maple forest destroyed by earthworms, and B is the ash soil without earthworms
As the climate warms, earthworms are also expanding their territories northward. In the opinion of some researchers, the consequences will be catastrophic once earthworms appear in the boreal forests, which are very special. In warmer regions, forest topsoil consists mainly of minerals and organic matter. But in the boreal forest, the mineral and organic layers do not mix, and a thick layer of organic matter covers the mineral soil layer. This special kind of soil is called ashed soil (podzol).
A 2013 study published in Nature Climate Change estimated that earthworms around the world increase carbon emissions by 33% and other greenhouse gas emissions by 42%.
Unfortunately, something like this is happening. For example, a 2008 study published in Molecular Ecology found that Alberta, Canada, has seen large numbers of Dendrobaena octaedra (red earthworms) from Europe, which may have hatched from egg cocoons mixed in the sand of car tires or shoe soles, or may have been done intentionally.
Earthworms hatching from egg cocoons
When Americans and Canadians see their forests going bald, it may be hard to imagine that the "beneficial worms" that Darwin praised were the cause of all this.
