{"id":325,"date":"2016-04-12T09:51:23","date_gmt":"2016-04-12T14:51:23","guid":{"rendered":"https:\/\/uwm.edu\/field-station\/?p=325"},"modified":"2017-03-12T12:37:38","modified_gmt":"2017-03-12T17:37:38","slug":"earthworms-enhanced","status":"publish","type":"post","link":"https:\/\/uwm.edu\/field-station\/bug-of-the-week\/earthworms-enhanced\/","title":{"rendered":"Earthworms Enhanced"},"content":{"rendered":"

Howdy, BugFans,<\/p>\n

They\u2019re baaaccckkk! April (and March) Showers bring more than May Flowers, they revive the earthworms that \u201cslumbered\u201d below the frost line all winter. Here\u2019s an enhanced version of a BOTW that appeared in 2009. This episode demonstrates once again that the BOTW definition of \u201cbug\u201d is closer to that of a first grader than that of an entomologist.<\/p>\n

In her childhood, the BugLady was deeply moved when a character in the play Teahouse of the August Moon<\/em> said \u201cWhen you kill a worm, you kill a friend.\u201d Worms, we are told, honeycomb the soil with their tunnels, letting in air and rain; their slime glues soil granules into clumps; and they build new soil with the deposits (worm castings) that mark their passing. Soil engineers is what they are. Happy earthworms make happy gardens!<\/p>\n

So, in the ensuing decades, when it \u201crained worms\u201d (rained so much that their tunnels flooded and worms were displaced to sidewalks and parking lots), she rescued these \u201croad-worms\u201d and deposited them in the moist grass instead of leaving them for hungry birds or for the noonday sun. Why did the earthworm cross the road? Several on-line sources are \u201crain-worm deniers,\u201d stating that worms do not get tired of treading water, that they can breathe well enough in wet soil, that they\u2019ve simply decided to broaden their horizons, or that they\u2019re out because it\u2019s cloudy, or that they\u2019re taking advantage of the damp conditions to reproduce (they mate at the soil\u2019s surface).<\/p>\n

Then the BugLady learned that Wisconsin earthworms are aliens that damage forest ecology! More about that in a sec.<\/p>\n

There are about 180 species of earthworms (class Oligochaeta) in America, and 6,000 species in the world. Of those, only about 150 species are widely distributed, \u201ccosmopolitan\u201d worms.<\/p>\n

Earthworms live in U-shaped tunnels in the soil. They stay indoors during the day and emerge at night because sunlight\u2019s UV rays are toxic to them, paralyzing them, damaging muscle cells, and ultimately drying out the moist skin through which they breathe (there are studies indicating that earthworms may turn out to be useful as UV monitors for humans). They\u2019re at risk even on cloudy days. They live in the dark. Eyeless, they sense light with their skin, and earless, they are tuned in to vibrations. They are, literally, front-loaded, with a brain, five \u201chearts,\u201d and other organs at the head end. Nerves stretch the length of their body, their sense of touch is well developed, and there are many chemoreceptors located near the mouth.<\/p>\n

An earthworm\u2019s smooth, moist skin, with its rows of setae<\/em> (bristles), overlays an impressive musculature. Progress through the dirt (or resistance to potential predators) is achieved by extending their front end, swelling it so it fills\/jams the circumference of their tunnel, allowing the bristles to grip, and then contracting its rear half. And, yes, if enough of the front half of an earthworm is separated from its rear half by a shovel or a tug-of-war, the front can regenerate a portion of its \u201ctail.\u201d The\u00a0naturenorth.com<\/a> website says that if you put a big night crawler on a piece of paper, you\u2019ll hear its setae scratching as it locomotes. The BugLady loves that warm evening in early spring when earthworms come up to rustle the dry leaves.<\/p>\n

When a young worm\u2019s fancy turns to love, any old earthworm will do. Earthworms are hermaphrodites—male and female in a single body. Each individual produces both eggs and sperm (they do not self-fertilize), and they clasp together to exchange sperm. Research suggests that they may use pheromones to locate their significant other, down there in the dark.<\/p>\n

Worms eat organic material, including dead leaves (they prefer leaves with a high sugar content like maple and birch), small soil invertebrates, bacteria, and fungi that they ingest as they move through\/excavate their tunnels. In loose soil, they are picky about what they eat; in compacted soil, the only way forward by ingesting everything. As a result of its trip through an earthworm, material is broken down into smaller pieces and its pH is brought closer to neutral before the residue is deposited on the surface as a worm casting. Check out Life in a Bucket of Soil<\/em>, by Alvin and Virginia Silverstein and Discover Nature Close to Home<\/em> by Elizabeth Lawlor for great descriptions of the earthworm lifestyle.<\/p>\n

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What eats worms? What doesn\u2019t? They\u2019re an important strand in the food web. According to the naturenorth.com<\/a> website, \u201cFor animals that weren\u2019t originally found in Manitoba, worms now fill a very important slot in the food web.\u201d<\/p>\n

Soils that the glaciers chewed up, froze, compacted, transported, and spit out ended up earthworm-free, and the plant communities that became established in those post-glacial soils evolved absent the considerable impact of worms. The BugLady still hasn\u2019t heard a satisfactory answer about Wisconsin\u2019s Driftless Area, which, although it was untouched by the most recent glaciation, was still exposed to permafrost conditions caused by the flow of frigid air down the slopes of the ice sheet.<\/p>\n

At its maximum, the most recent glacier extended into central Iowa, Illinois, and Ohio. According to the people who measure these things, earthworms move at a top speed of about 5 \u00bd yards a year. They did the math and found that on their own, earthworms might have trekked north approximately 35 miles in the last 11,000 years. So, earthworms must have gotten a little help. Alien earthworms were introduced to the upper Midwest when settlers imported bulbs and fruit trees from the Old Country, from dirt that was used as ballast on ocean-going ships, and by people hoping to improve soil structure. Worm introduction continues today through landscaping projects and recreation—fisher people, please take note—earthworm populations are densest near lake shores where bait buckets are emptied at the end of the day.<\/p>\n

Earthworms live up to their reputations as soil builders, and although their contributions to farming and gardening are not argued, their impact on forests is profound and negative. In forests that developed after the glacier withdrew, the decomposition rate of organic matter on the forest floor was slow, accomplished by bacteria and fungi and tiny critters that made big pieces into little ones, creating below the trees a soft, deep, nutrient-rich \u201cduff\u201d that sheltered small animals, acted as an insulator, and provided mulch for wildflowers and seedlings to grow in.<\/p>\n

In contrast, earthworms compete with some important fungi (and eat others), and they mix, rearrange, compact and eat leaf litter, duff and top soil layers, making conditions hostile for seeds. And in the process, the worms also eat seeds, depleting the seed bank and hampering future regeneration. With the character of the forest floor altered and the nutrient cycle disturbed, ground-dwelling animals both tiny and large lose their homes and their food, setting the stage for additional alien \u201cgeneralists\u201d and lowering biodiversity. As many as 80% of terrestrial plants are able to grow because they form mycorrhizal<\/em> partnerships with fungi that enable them to take up nutrients and water. Research is being done to explore the impact of alien earthworms on soil fungi and therefore on plant communities.<\/p>\n

Fun Earthworm Facts:<\/p>\n