I suspect as you read this, the cacophony of cicadas outside is probably reaching its climax. And as the males die, shortly followed by the egg-laying females, a gluttony of food will be devoured by any number of predators. Birds, shrews, foxes, raccoons, opossums, snakes and frogs, will all soon be satiated with this plethora of protein. Of course, our cats and dogs will have their turn at playing with, and eating these easy targets. I would suggest keeping Fido off your new carpet for the first several days of encounters until he has learned when to say when.
Eventually, all of the cicada corpses will be returned to the soil. At that point, the invertebrates, bacteria and fungi of the soil community get their chance at the grounded gourmet. Included in this community are the 50 to 500 earthworms that inhabit every square yard of soil.
Earthworms are an important part of our environment. In fact, Charles Darwin’s last book, The Formation of Vegetable Mould, published in 1881, was the first methodical study of earthworms. It was referred to as the culmination of his professional activities (at least, according to modern worm scholars). Darwin noted “It may be doubted whether there are many other animals which have played so important a part in the history of the world…” Certainly, earthworms are valuable in their ability to improve soil structure, mix and till the soil, aid in humus formation, and increase the availability of plant nutrients. In fact, Darwin concluded that earthworms brought 18 tons of soil to the surface per acre each year, a figure supported by current studies.
Science is now discovering that all is not well in the soils of North America. Once again, it appears a case of introduced species disturbing the balance that exists among the native community members. An estimated 70 species of native earthworms can be found in the Eastern United States, while about 45 non-native species have been introduced. And, the question is only now being addressed as to what is the impact of these foreign invaders.
Researchers participating in the All Taxa Biodiversity Inventory in the Great Smoky Mountains National Park have found a region where the duff (or partially decomposed surface leaf layer) was significantly missing. Instead of the rich organic matter that typifies the forest floors of the area, researchers found unusual, squiggling gray Asian earthworms of the genus Amynthas, and a healthy load of their excrement.
The concern of this situation is the loss of the duff layer, with its community of insects and microorganisms. Compared with the more leisurely feeding rate of these smaller organisms, earthworms consume the leaf litter 24 hours a day. They digest it so quickly, that whole populations of microorganisms are at risk of being wiped out in some areas.
The duff layer is the forest's digestive system. Its microbes and fungi break organic matter down into essential elements such as nitrogen and phosphorus so that plants can absorb them to start the cycle over again. Its entangled litter creates cover and food for larger members of the community: insects, spiders, salamanders, frogs, small mammals and migratory birds. A duffless forest floor can't support spring ephemerals like bellworts, trillium, yellow violets and wild ginger. Instead, exotics such as garlic mustard can muscle in, taking up space and shading out native flowers and tree seedlings.
The impact of introduced worms is best documented in the glaciated regions of northern US. Here, all native worms were removed by the glaciers some 10,000 years ago, being replaced in the past 200 years by European and Asian worms brought in by the early settlers. Prior to the introduction of worms, the ecological communities were based on nutrient poor, acidic soils. Since their introduction, the worms have added soil nutrients, raised soil pH, reduced soil duff and removed mycorrhizal fungi necessary for certain plants, including the rare goblin fern found in the Chippewa National Forest of Minnesota. Salamanders have also been notably decreased in numbers as well, due to the reduced food source formerly found in the duff layer. This, in turn, will have an affect on the predators of salamanders, namely the snakes, shrews, and birds.
So, we ask, are worms our friends or not? And, of course the answer is that it depends on the species and where they are found. Native species tend to be controlled in numbers by natural predators, and thus don’t tend to significantly impact the duff layer as the uncontrolled high number of exotic worms. Perhaps in the garden and agricultural endeavors introduced worms may prove to be beneficial in aerating and breaking down inorganic soils. But in our forests, the more adaptable, non-native earthworms are known to devour the leaf litter that is vital to the healthy functioning of forests in northern North America, altering soil conditions, enabling the spread of invasive plant species and changing the food chain for forest animals.
Earthworms belong to the Phylum Annelida, a word derived from Latin meaning "rings." You'll note that worms are made up of dozens of rings or segments. The phylum includes earthworms and their relatives, leeches, and a large number of mostly marine worms.
Most earthworms are hermaphroditic with both male and female gonads. It is a myth that you can divide a worm in half and have each half grow into a complete new worm. But to some degree, worms can regrow segments that have been cut off. A worm can lose its head, but it'll grow right back as long as too many segments haven't been sacrificed. Each ring or segment on the worm has tiny bristles that help the creature move along the ground or burrow through the soil. There are approximately 4,400 named species of earthworms around the world - some measure only about one inch long. The giant earthworm of Australia can measure ten feet in length and has a girth of up to three inches!
Researchers have broken worms into three categories, largely descriptive of their habits in the soil. These three categories are endogeic, anecic and epigeic. Endogeic worms are the only ones that actually eat soil, make lateral burrows in the shallow soil, but rarely come to the surface. Anecic worms, like the non-native night crawlers, dig vertical tunnels up to six feet in depth, and feed at the surface. The epigeic worms, like the ‘red wigglers’, live in the surface soil and duff layers and are used in vermiculture for composting purposes. They are apparently native to North America.