But whether they are helpful or harmful remains unclear. Dennis Whigham and Katalin Szlavecz prepare to send a jolt of electricity into the soil to draw earthworms to the surface. When materials decay, they release CO 2 into the atmosphere. Over the short-term, earthworms appear to speed up the process. They break down leaf litter and wood much more quickly, causing microbes to release more CO 2 than they would otherwise.
But over the long term, the team suspects they could do the exact opposite. Earthworms excrete some of the soil they consume in tough pellets called casts. These casts take more time to break down—perhaps making it so the carbon stored there stays in the ground longer. In short, the invading army of earthworms could threaten the planet just as it threatens individual forests. Or, at a critical moment, they could turn into surprising allies. Find out how earthworms can transform forest soil communities and impact plant growth in the Molecular Ecology Lab.
Smithsonian Environmental Research Center. And European earthworms live on every continent except Antarctica. But of all the earthworms people have shuttled around the world, the ones Dobson shows me at Seton Falls have scientists most concerned. Originally from Korea and Japan, they are known as jumping worms , snake worms , or crazy worms. And they have the potential to remake the once wormless forests of North America.
For their stellar reputation, they can thank none other than Charles Darwin. In addition to developing the theory of evolution, Darwin studied earthworms for 40 years at his home in England. With characteristic curiosity and rigor, the naturalist conducted all manner of earthworm experiments: He observed their reaction to the sound of the bassoon none and to the vibrations of a C note played on the piano panic.
He watched how they pulled leaves into their burrows, and tested their problem-solving skills by offering them small triangles of paper instead most figured out how to drag them by a corner.
Darwin also measured how quickly worms covered up a large paving stone in his garden with their castings. He estimated that they could move at least 10 tons of soil per acre per year. Read: A creationist sues the Grand Canyon for religious discrimination. But in , shortly before his death, Darwin compiled his worm studies into a book called The Formation of Vegetable Mould through the Action of Worms with Observations on their Habits , in which he praised the humble critters.
And though they can be helpful for breaking up compacted soils and breaking down organic matter, worms can also cause trouble in agricultural fields. Their burrows create channels that allow nutrients and pesticides to leak from fields into nearby waterways, and carbon dioxide and nitrous oxide to escape into the atmosphere.
In fact, a review of recent research found that worms likely increase greenhouse-gas emissions. T he mustard pour , which Dobson had done partly for my benefit and partly just to check in on the worm population, is over a few minutes after it begins. The worms—bothered but otherwise unscathed—have disappeared back into the forest floor.
So Dobson and I head back to where we left her assistant, Mark, toiling among a jungle of knee-high poison ivy and Johnny jumpseed. Her goal is to track them as they grow and reproduce to see if they show any potential of adapting to jumping worms. Mark, an undergraduate at the University of Connecticut, is doing his best.
We pile into her silver Subaru Impreza, where the dashboard thermometer reads 38 degrees Celsius— degrees Fahrenheit. Dobson and her car are both Canadian. Inside the restaurant, air conditioning and cold beverages revive our spirits. Common species like Lumbricus terrestris , better known as the night crawler, arrived hundreds of years ago with European settlers, and have long been welcomed in gardens and farmland. In the s, however, researchers began to find European worms in the forests of Minnesota and other northern states.
One hypothesis is that people spread them when they throw away extra fishing bait next to lakes and streams. The discovery alarmed scientists. In the absence of worms, North American hardwood forests develop a thick blanket of duff—a mille-feuille of slowly decomposing leaves deposited over the course of years, if not decades.
That layer creates a home for insects, amphibians, birds, and native flowers. But when worms show up, they devour the litter within the space of a few years. All the nutrients that have been stored up over time are released in one giant burst, too quickly for most plants to capture.
And without cover, the invertebrate population in the soil collapses. Where millipedes and mites once proliferated, now there are only worms. With their food and shelter gone, salamanders suffer and nesting birds find themselves dangerously exposed.
Or that native species, accustomed to spongy duff, are ill-prepared to root into the hard soil left behind when the worms have finished eating. It could be all of the above. Perhaps most worryingly, early studies suggest that worms can sometimes halt the regeneration of trees. His theory is that the worms take out all the understory plants, leaving nothing for deer to chew on but the young trees.
Read: How to make a half-gallon of maple syrup in 20 easy steps. These sweeping powers are why earthworms are often called ecosystem engineers. And Dobson and her colleagues fear that jumping worms pose an even greater threat than their European predecessors.
Jumping worms appear to have many of the same effects, except that they grow larger and exist in dense colonies, sometimes numbering more than a hundred individuals per square meter of ground.
And while European worms range throughout the upper four to six feet of soil, jumping worms stick to the top six inches or so, churning it relentlessly into a loose sediment that Dobson likens to ground beef.
Others I talked to compared it to coffee grounds. The disturbed soil erodes easily, dries out quickly, and generally makes poor habitat for many plants. While there, he cursed the lack of understory in which to take cover during tactical exercises.
Dobson explains that the worms act like a funnel, winnowing away the diversity of the forest. First, they take out the most sensitive native plants, leaving only hardy species like poison ivy and Virginia creeper. Then they prime the ground for invasives. Even more than their European relatives, jumping worms seem to reshape the forest from the ground up.
U ntil it moves , a jumping worm looks a lot like any other earthworm: long and thin, with rosy brown skin divided into bellows-like segments. Experts will tell you to look at the clitellum—the band that holds the reproductive organs of worms, which are hermaphrodites. In European worms, the smooth, pink clitellum is found closer to the middle of the body. There are many species of jumping worms. The first arrived in the United States in California in the s.
Others have been in the Southeast for more than a century—long enough to earn colloquial names like the Alabama Jumper. You can buy these online, too, but worm experts advise against spreading them.
The three species that Dobson and others worry most about are newer arrivals, and likely hitchhiked on imported plants, where they caught the attention of groundskeepers.
An oft-repeated anecdote holds that jumping worms first appeared in Washington, D. By the s, they were spotted at the Bronx Zoo, where one species was later raised to feed the resident platypuses. Earthworm activity facilitates the physical comminution of organic particles, the amelioration of soil pH, the enhancement of microbial activity, and the mixing of soil from different strata in the profile. They promote the formation of organomineral complexes and, by delivering faecal casts at the surface, they bring organo-mineral crumbs from the deeper parts of the profile to the surface.
Earthworms also facilitate the transport of certain elements to the soil surface so that their faecal casts have concentrations of calcium, sodium, potassium, magnesium, available phosphorus, and molybdenum that are higher than in the surrounding soil. Therefore, earthworms not only improve the soil texture but also enrich the soil [ 3 , 9 , 10 , 15 ]. Darwin suggested that earthworms may change the chemical composition of materials that pass through their gut.
However, there is still little evidence that they can accelerate the alteration of parent materials or the breakdown of larger soil particles [ 11 ]. Some work with the large Octodrilus sp. If other earthworms are able to do this, then it is an important finding because sorption of radiocaesium on illitic-type clay minerals served to reduce the amount of radiocaesium entering terrestrial and freshwater food chains after the Chernobyl accident of 26 April [ 17 ].
Most of the radiocaesium became fixed in the interlayers between the platelets of the illite minerals. Thus, when the Chernobyl plume passed over Northwest England and it rained, the effects of the radiocaesium fallout varied considerably among lakes in the area and fish in the lakes [ 18 — 21 ]. In lakes with illitic minerals in their catchment, levels of radiocaesium decreased rapidly in the water, sediments, and fish, presumably because most of the radiocaesium was trapped in the catchment.
In contrast, levels remained high in the water, sediments, and fish of lakes surrounded by acid moorland. The most controversial section of Darwin's book dealt with earthworm behaviour and if they could be described as intelligent.
This section was chiefly responsible for the popularity of the book. The poor worms were subjected to various tests, including response to touch and vibrations, strong breath and odours, a wide range of foods e. He also concluded that they had favourite foods.
Darwin observed that earthworms plug the mouth of their burrows with leaves, leaf stalks, or twigs and considered that an intelligent animal would draw such irregular-shaped objects into a cylindrical hole by their narrowest part Figure 2. Therefore, he placed around the burrow entrance leaves of various native and foreign plants and triangular pieces of paper of various sizes.
In the majority of trials, these objects were drawn into the burrows by or near their narrow apex. The only exception was pine needles that were drawn in, by, or near their base. Before considering this conclusion further, it is useful to compare earthworms with their cousins, the leeches. Both belong to the phylum Annelida and both are hermaphrodite with some segments near the middle of the body modified in mature animals to form a clitellum that secretes a cocoon for the eggs see Figure 4.
Hence, they are regarded as subclasses Oligochaeta and Hirudinea of the class Clitellata [ 11 , 22 ]. Unlike earthworms, leeches are active predators [ 22 — 25 ]. Some species suck the blood of their prey whilst other species suck in their whole prey or devour pieces of moribund or dead animals. They have fewer segments than earthworms and a more compact, muscular, body with anterior and posterior suckers.
Leeches are good swimmers but also travel by looping, using their suckers. Their sense organs are well developed so that they can detect movements of potential prey and chemicals released by injured prey. Most species have more than two pairs of eyes that can detect changes in light intensity and direction. The medicinal leech can also detect the warmest parts of its mammalian prey where it sucks its blood meal [ 26 ]. With such a range of senses, it is not surprising that leeches have a well-developed brain consisting of a fusion of ganglia in the anterior segments of the body.
Leeches can therefore react rapidly to a wide range of stimuli but it would be wrong to regard them as intelligent; their behaviour is instinctive [ 23 , 24 ]. There are no definite eyes, but light-sensitive cells occur on the dorsal surface, especially at the anterior and posterior ends of the body, the regions most frequently exposed to light [ 11 ].
As noted above, they must have sense organs that are sensitive to chemicals, changes in temperature, and especially touch and vibration transmitted through solid objects. Like leeches, their behaviour is instinctive and it is wrong to describe them as intelligent animals.
Darwin's last monograph was published in October [ 2 ]. This book was distributed one year later in the United States of America via the publisher D. Appleton and Company , New York. Darwin's powers of work are inexhaustible, and not less remarkable than his genius. Darwin's little volume on the habits and instincts of earth-worms is no less marked than the earlier or more elaborate efforts of his genius by freshness of observation, unfailing power of interpreting and correlating facts, and logical vigor in generalizing upon them.
All lovers of nature will unite in thanking Mr. Portions of his book read almost like a romance, for there is much in his revelations of surprising strangeness and novelty.
These statements on Darwin's last publication and his general conclusions concerning soil biology and so forth. Only five months later, on 19 April , Charles Darwin died. In his most famous book On the Origin of Species [ 27 ], Charles Darwin did not define what species are and how they can be distinguished from varieties [ 29 ].
Darwin's relaxed opinion concerning species definitions may have been the reason why he did not identify the species of earthworms he was investigating [ 28 ].
It is likely that Darwin [ 2 ] studied the most abundant burrowing anecic earthworms of Britain, Lumbricus terrestris widespread , L. However, it is well known that in southern English grasslands, 8 to 10 earthworm species occur [ 29 ]. The common earthworm L. The oligochaetes forage and mate on the surface at night Figure 2.
After heavy rainfall and inundation of the soil, the oxygen-dependent aerobic invertebrates escape from their anoxic burrows and creep over the moist soil. During these forced excursions, most of the free-living earthworms are eaten by predators birds, etc.
Representative specimens of two common earthworm species that were captured after a heavy rainfall in Germany L. However, he only briefly mentioned the reproductive biology of these terrestrial oligochaetes. Four decades later, a detailed description of the reproductive biology of the common species L. Oligochaetes earthworms and hirudineans leeches class Clitellata are simultaneous or protandrous hermaphrodites with reciprocal insemination [ 23 , 24 ]. In other words, in contrast to gonochorists, hermaphrodites function as males and as females.
The mating process of L. During these nocturnal episodes, which last from one to 3 hours, the partners remain anchored in their home burrow with their tail end, which permits a rapid retreat in case of an attack of a predator.
During copulation, both worms establish a contact to the clitellar region of the partner see Figure 4. During this tight body contact, both partners exchange sperm and hence function as males. After reciprocal insemination is finished, the worms separate from each other, a mechanical process that can cause severe body damage due to the partner's sharp copulatory bristles setae.
According to Michiels et al. As pointed out by Nuutinen and Butt [ 32 ], L. In general, the mating process in L. Several days after copulation, the earthworms act as females and produce lemon-shaped capsules cocoons that contain 5 to 8 fertilized eggs via their clitellum, a process that resembles that of worm-leeches of the genus Erpobdella [ 23 , 24 ].
The dense forests consist mostly of pines Pinus sylvestris and Norway spruce Picea abies , which are grown in many places as commercial monocultures. In addition, beech Fagus sylvaticus forests form integral parts of the lower regions of this unique landscape in Southern Germany. More than a century ago, the German annelid specialist W. Michaelsen investigated the soil of the southern part of the Black Forest, but no common earthworms L.
However, he discovered a single individual of an unidentifiable earthworm that he later described as L. Later, it was discovered that this large earthworm Figure 6 represents a separate biospecies that is not closely related to the widespread L. In contrast to the common earthworm L.
When fully extended, adult L. In Figure 7 , an adult L. Both animals were collected in the same habitat. The enormous body size of the giant Black Forest earthworm becomes apparent [ 35 ]. In forests with large litter layers, the usually deep-digging anecic species L. Detailed studies have shown that the Black Forest earthworm Figures 6 and 7 displays a switch from an epigeic to an anecic burrowing way of life during its ontogeny.
This aspect of the life cycle of L. After decades of research it is now definitively clear that the giant earthworm L. Detailed biogeographic studies on the occurrence and habitats of the sister taxa L. The young founder populations of ancient L. As mentioned above, the common species L.
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