Download Invasive Earthworms

Invasive Earthworms
The Silent Killers of our Natural Forests
Authors: Aubrey Weibel, Michael Wolenter, with Julie M. Fagan, Ph.D
Abstract:
The presence of earthworms in the soil is thought by many to be a good thing.
Earthworms aerate the soil, break down decaying plant matter, and mix and fertilize the
soil with their waste matter. However, most people do not realize that earthworms are
not native to North America, and are known as an invasive species. It has recently been
discovered that earthworms are actually destroying the understudy of many of our
natural forests. There is no current and effective means to eradicate these pests, and
the only defense we have is preventing the spread by humans. We will be looking to
educate fishermen about the danger of spreading worms either through the route of
educational information handed out at the purchasing of a fishing permit or to attempt to
get worm retailers to label their products with a warning that these worms are invasive
and cannot be released live into the ecosystem.
Video Link: http://youtu.be/uH74vlcHoms
Invasive Species: What are they and how did they get here?
An Invasive, or non-native, species is an organism that has been introduced into
a new ecosystem. Invasive species are a growing problem around the world for a
number of reasons. The greatest concern comes from the ability of invasives to out
compete native species for available resources. However, in the case of invasive
earthworms, they are not out competing since there are no other species that fill that
same niche. Rather it is the filling of the niche that is causing a problem. Aside from the
case of invasive earthworms, these invasions occur in many cases in a variety of
ecological systems.
An example of a more normal invasive species would be the mile-a-minute weed.
This plant was introduced from a foreign country where there are a large number of
consumers and diseases that would naturally inhibit the growth of these slender plants;
however, when the weed was introduced to the United States, the biological controls
were left behind. Therefore, it has been able to grow uninhibited in competition with
other plants. In the case of mile-a-minute weed, the uninhibited growth is enough to
allow it to strangle and kill both native grasses and agricultural field crops. For this
instance of an invasive species, it has been possible to introduce a biological control
that would use the mine-a-minute weed and only the mile-a-minute weed as a host.
Invasive species are not limited to just plants, an invasive organism is truly any
living creature that is disturbing the natural environment with its presence. There are
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many cases of invasive animals such as the asian longhorn beetle and the emerald ash
borer. These small insects have caused the death of thousands of trees in many
regions. They both had entered the United States through contaminated wooden
shipping pallets and would then be free to bore into living trees in the new region they
had been imported to and reproduce. The possible transportation of this invasive by
humans was one of the greatest concern for researchers.
Not all invasive species are always quite so obvious in their harmful nature
though. Some may even seem beneficial initially; however, our regional environments
have formed to be very delicate and complex systems. Small change can often lead to
major impacts on the system over a long period of time. One such story is that of the
earthworm, we are only beginning to see the impacts of earthworms that have been
introduced to regions that had not had any exposure to them in the past.
The Invasive Earthworm: Lumbricidae
Environmentalists have performed studies to determine what regions of the
United States had native worms and which did not. Patterns were often clear cut along
glacial paths and major ecotone boundaries. It is believed that as the glaciers moved
along the continent, they also killed off any native worms that had been in the region,
and because of the earthworms poor locomotion skills, they cannot migrate quickly to
new regions. However, when transported by humans, they can cross thousands of miles
in a day.
For invasive worms in the United States, the group that is of most concern are
those that belong to the suborder Lumbricidae. Lumbricidae, more commonly known as
earthworms, are believe to have first arrived to the United States by the arrival of
European settlers who would often use soil containing the worms or their eggs, to
balance their ship’s weight. Tiunov, et al (2006) demonstrated the invasion pattern of
earthworms in North America is closely linked with patterns of human activity and land
use practices. Demonstrating again that humans ourselves are a primary mode of
transportation for these pests.
Earthworms: The good, the bad, and the invasive
Earthworms are not entirely without use, they do serve a great amount of good in
many cultural practices in the United States. The earthworms can help to aerate
compacted soils on sites that have been damaged by heavy machinery. Earthworms
also do a great job of creating suitable growing conditions for agricultural crops. Their
ability to naturally integrate organic matter into topsoil is unmatched by any other
organism or machine. The incorporation of organic material into agricultural soil is
essential to create a good soil-ecology, and is very useful in soils that get quick turn
arounds every year.
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It is the worms very ability to turn around organic matter so quickly that is both its
best and worst quality. For agricultural purposes, quick turn around is an asset, but in
natural ecosystems this is not a benefit. Many ecosystems have formed around organic
matter that has built up over the years. By having earthworms introduced to new
locations so rapidly by human transportation, it is inevitable that they will have a
negative impact on the ecosystems they are introduced to. Native worms do exist in
some parts of North America, but because of their slow migration patterns they have
remained isolated without facilitated transportation. (Cameron, 2009)
Biology of the Earthworm
Earthworms have a variety of means of reproduction, allowing them to be hardy
organisms in nearly all environments. The earthworms are able to both regenerate their
body to reproduce asexually and sexual reproduction to produce new offspring. (Butt,
1993) The adaptability of these worms that allows them to reproduce so rapidly makes it
a difficult to control them once they have been introduced into a region. Therefore it is
most beneficial to prevent these worms from ever being introduced in the first place.
Ecological Effects: Why are Worms Useful
Earthworms move through soil, digesting organic matter as they move through
the various layers of soil. In highly compacted soil, this results in macro-pores, which
allows for greater water movement and better root access in the earth. By aerating the
soil, this allows for more plant growth (Holdsworth, Hale, and Frelich). Earthworms also
incorporate nutrients into overly mineralized soil are capable of moving the already
present nutrients closer to the surface, further promoting plant growth. As earthworms
move through the soil, creating the macro-pores, they are also loosening, mixing and
fertilizing the soil with their waste matter. They eat decaying plant matter, breaking it
down and recycling the nutrients for easy use by local plants (Coles, and Walker).
Hopes for Earthworm Usage:
There are hopes that strategically introducing earthworms into decimated
habitats, such as deforested lands in the amazon, will help to prevent erosion. The alien
species are highly adaptive and can acclimate to a new environment, such as a
deforested plot of land, much faster than native fauna. The worms also increase the
mineral levels of Nitrogen and Phosphorus in depleted soils. Earthworms even stimulate
plant growth, though most of the plants they create habitats for are also non-native and
a threat to the natural landscape (Coles, and Walker).
How Invasion is Still Occurring:
Since earthworms break down plant matter efficiently, many people use them for
vermicomposting, or using earthworms do compost their food waste faster than it would
decay in a compost bin outside. Unfortunately, this is one of the ways that earthworms
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are being spread – inside the buckets of nutrient rich composted fertilizer are earthworm
eggs which hatch in whichever site the soil gets placed.
Earthworms are also used as fishing bait, as they are so abundant in the local
soils. However, when a fisherman is done with the day and has not used all of his bait,
most often, the fisherman will discard the extra worms in the soil, introducing them to a
new habitat and allowing them to reproduce and completely change the ecosystem in a
few years.
Why are Worms Detrimental:
Earthworms have successfully invaded every continent of the world (excepting
Antarctica) (Coles, and Walker). The invasive species of earthworms in North America
(such as the species A. hilgendorfi) grow and mature extremely quickly, resulting in a
low generation time and high populations. Once established, an earthworm population
is almost impossible to remove (Tennisen). However, on their own, earthworms will
cover a maximum distance of half a mile in 100 years, moving only a few feet every
year (Holdsworth, Hale, and Frelich).
Overall, there are about fifteen species of earthworms introduced in North
America, and they are out competing the local wildlife for resources. They also adapt
more quickly to deforestation and cultivation of land, which gives them a jump start on
many of the local species. Even in some areas of North America where glaciers were
not found, the invasive species are out competing and even sometimes eradicating the
local worms which have been there for thousands of years. But local species of
earthworms are not the only ones to suffer (Bienkowski).
In a study done in Michigan, scientists created an environment with both
millipedes and invasive earthworms. Because both organisms use the same food
sources and the earthworms were more adept at finding and consuming the organic
matter, the millipedes were greatly out competed by the earthworms. However, it was
also found that when the millipedes were still present, they slowed the reproductive rate
of the earthworms by using the earthworm eggs as an alternative food source. When
the millipedes population decreased due to lack of food sources, the earthworm
population began to increase more rapidly again, as there was no biological control in
place (Coles, and Walker).
Earthworms are Changing the Ecosystem:
Earthworms are capable of making one certain kind of soil to live in, weather that
means improving or degrading the quality of the ecosystem they inhabit. Just as
earthworms can take a mineralized, nutrient poor soil and improve it through breaking
up decaying organic matter. The earthworms can also take an established understory
and destroy its soil quality by removing the essential layers of organic matter that
protect the soil surface, exposing it to all forms of erosion (Bienkowski). When
earthworms are introduced, the soil chemistry of the surrounding area can also be
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affected by the invasion. Through the decomposition of leaf litter in a forest, worms not
only increase the organic matter of the soil but also the ambient nitrogen and
phosphorus levels in the soil. This can lead to drastic changes in the microclimates that
facilitate the carbon and nitrogen cycles. (Coles, and Walker).
Specifically, duff is the spongy layer of decomposing leaves, moss, and other
biological materials that make up the decaying organic matter on the forest floor. It is
used to protect the youngest parts of the understory, the saplings and the smaller
woody bushes from malnutrition, erosion, and exposure. The forests have evolved with
the spongy duff layer, and now need that layer to survive and reproduce (Holdsworth,
Hale, and Frelich). When the earthworms are introduced, they begin to decompose the
duff layer much faster than it is meant to be, and over a few years the duff layer can
completely disappear (Tennisen).
With the disappearance of the duff layer, many small saplings, wildflowers and
ferns are now unable to reproduce in these forest. The earthworms actually increase the
density of the spongy duff to soil, which prevents water infiltration (Holdsworth, Hale,
and Frelich). With the loss of the duff layer, the ground loses its shade covering.
Exposing organisms living in the soil to heat from the sun. This temperature shift is
actually causing some tree species to shift farther north in America to maintain their
specific temperature zone (Bienkowski). Once the duff layer is destroyed, many of the
wildflowers and seedlings are incapable of reestablishing themselves in the forest and
can be lost entirely to that region. The loss of the duff layer can cripple the biodiverity of
a forest in ways that could not be recovered.
In addition to exposing understory organisms to harsh conditions, the loss of the
duff also creates opportunities for other invasive organisms to come into the ecosystem.
Particularly invasive organisms that had previously been competing with the native
organisms for their shared niche. Many of these invasives are highly adept to growing in
the marginalized soil left behind after the duff has been decayed. As these invasives
continue to fill the specialized niches that had once been filled by native species, the
biodiversity will continue to decline. (Melanchier).
Earthworms will often eat whatever form of organic matter that they can find in
the soil that they occupy. Sometimes this includes the beneficial fungi surrounding plant
roots that help the plant increase its ability to absorb nutrients and minerals from the
soil. When the earthworms strip the plants of these beneficial fungi, it can be very
detrimental to the growth of young plants, in many cases, preventing them from
competing with other plants leading to the death of the plant.
Not only can earthworms prevent the growth of new plants and cause the death
of living ones, but they have also been found to eat more than just decaying plant
matter and fungi; they can at times even consume living plants and seeds as well. In a
recent study, earthworms have been discovered to seek out slow germinating, Nitrogen
rich plant seeds and seedlings to consume them. This is not the same consumption as
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a bird eating a berry, as the bird only ingests the fleshy part of the fruit and transports
the seed elsewhere to germinate; in this instance the earthworm ingests the seed itself,
killing the plant. The earthworm derives a nutritional benefit from the consumption, but
with the population of earthworms in the ecosystems currently, they are destroying all
hopes of plants with Nitrogen rich seeds from reproducing, which could bring about the
extinction of some slow germinating plant species in North America in the near future.
The only way to prevent this is to stop the spread of earthworms in the country (Walker).
Summary of Ecology:
Earthworms have some benefits that we can use to improve certain soil qualities
through vermicomposting, but they must not be allowed to enter our ecosystem more
than they already have. People underestimate their destructive power because they are
small, slow moving and look harmless, but they can destroy an entire ecosystem in a
few years. When given an area that has not evolved to deal with earthworms, the
worms will destroy the soil quality, breakdown the essential duff layer and consume
susceptible nitrogen-rich seedlings and the protective root fungi. The result of
earthworm invasion is extinction of local plant species and increase in invasive species
which have evolved to live with earthworms in the soil. Earthworms also cause erosion
and nutrient leaching, creating a much poorer soil for the plants to use and even
degrading fish habitats with the runoff (Holdsworth, Hale, and Frelich). There is no
current practical solution to this problem, and so the only hope we have is preventing
their spread by not releasing them into the soil. If we stop introducing the invasive
species, we may be able to preserve some of our untouched forests.
Our Potential Solution: Community Action Project
There have been many considered solutions to the invasive earthworm problem,
some of which could solve the problem adequately, but they are not viable financially on
a large scale that would be required in order to eliminate invasive worms. In vivo, it was
found that nanoparticles of Titanium Oxide and Zinc Oxide had toxicity to several
species of earthworms. Both forms of nanoparticles caused damage to the worm’s DNA
and mitochondria. However, the application of these powders over the large regions that
have been affected by the earthworms is unfortunately not a practical solution.
The best possible solution to the problem is prevention. Measures are being
taken to prevent further transport through agricultural channels; however, through our
personal research through the Internet, it has become clear that many regions of the
United States do not have regulations prohibiting the release of live bait. It is possible
that the release of live earthworms, particularly worms in the Lumbricidae group, also
known as nightcrawlers, can be of great concern to the natural habitat. Therefore our
Community Action Project will be focused on the education of fishermen through
providing information and literature to the Division of Fish and Wildlife, in hopes, that
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they might seek to implement regulations or at least seek to increase awareness about
the harms of releasing live bait.
Minnesota state has already implemented regulations prohibiting the release of
live bait into the habitat. Minnesota regulations states, “Dispose of unwanted bait,
including minnows, leeches and worms, in the trash. It is illegal to release bait into a
waterbody, release worms on the ground, and to release aquatic animals from one
waterbody into another.”
Our Potential Solution: Community Action Project
The best possible solution to the problem is prevention. Prevention of the
facilitated movement of invasive worms will remedy the problem in areas that still
remain free of these pests. Minnesota state has created regulations that prohibit the
release of live bait into the wild. The Minnesota law reads, “Dispose of unwanted bait,
including minnows, leeches and worms, in the trash. It is illegal to release bait into a
waterbody, release worms on the ground, and to release aquatic animals from one
waterbody into another.” By increasing awareness of these issues to wildlife and fish
and game associations within state government, it is possible that regulations can be
fostered to help protect our natural forests. We have written to our state legislatures as
well as the New Jersey Division of Fish and Wildlife in hopes that they will implement
regulations similar to those passed in Minnesota.
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Works Cited
Bienkowski, Brian. "The Underground Master of Invasive Species - Earthworms." Great
Lakes Echo. Greak Lakes Echo, 26 Sep 2011. Web. 6 Mar 2013.
<http://greatlakesecho.org/2011/09/26/the-underground-master-of-invasivespecies-–-earthworms/>.
Butt, K. R. "Reproduction and Growth of Three Deep-burrowing Earthworms
(Lumbricidae) in Laboratory Culture in Order to Assess Production for Soil
Restoration - Springer." Reproduction and Growth of Three Deep-burrowing
Earthworms (Lumbricidae) in Laboratory Culture in Order to Assess Production for
Soil Restoration - Springer. N.p., 01 July 1993. Web. 03 Mar. 2013.
Cameron, Erin K., and Erin M. Bayne. "Road Age And Its Importance In Earthworm
Invasion Of Northern Boreal Forests." Journal Of Applied Ecology 46.1 (2009): 2836. Academic Search Premier. Web. 6 Mar. 2013.
Coles, Jeremy, and Matt Walker. "Earthworm Invasion: Aliens Causing More Harm
Than Good?." Nature Features. British Broadcasting System, 24 Sep 2012. Web.
6 Mar 2013. <http://www.bbc.co.uk/nature/19646548>.
Holdsworth, Andy, Cindy Hale, and Lee Frelich. "Contain theose Crawlers!." Minnesota
Department of Natural Resources. Minnesota Interagency Exotic Earthworm
Team, n.d. Web. 6 Mar 2013.
<http://www.dnr.state.mn.us/invasives/terrestrialanimals/earthworms/index.html>.
Hough-Goldstein, J. et al. "Status of an ongoing biological control program for the
invasive vine, Persicaria perfoliata in eastern North America." 9 October 2011.
University of Delaware • College of Agriculture & Natural Resources.
<http://ag.udel.edu/enwc/research/biocontrol/documents/HGetal2012BioControl.p
df>.
Melanchier, A. "Invasive Earthworms in Northern Hardwood Forests." Wildlife
Gardeners. N.p., 21 Feb 2010. Web. 6 Mar 2013.
<http://www.wildlifegardeners.org/forum/feature-articles/5284-invasiveearthworms-northern-hardwoods-forests.html>.
Rose, Robyn. Asian Longhorned Beetle. 28 February 2013. USDA.
<http://www.aphis.usda.gov/plant_health/plant_pest_info/asian_lhb/index.shtml>.
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Tennesen, Michael. "Invasive Earthworms Denude Forests in U.S. Great Lakes
Region." Scientific American. Scientific American, 10 Mar 2009. Web. 6 Mar 2013.
Tiunov, Alexei, Cindy M. Hale, Andrew R. Holdsworth, Tamara S. Vsevolodova-Perel.
Invasion patterns of Lumbricidae into the previously earthworm-free areas of
northeastern Europe and the western Great Lakes region of North America. 25
May 2006.
Walker, Matt. "Earthworms Eat Live Seeds and Plants, Scientists Find." Earth News.
British Broadcasting System, 21 May 2010. Web. 6 Mar 2013.
<http://news.bbc.co.uk/earth/hi/earth_news/newsid_8694000/8694377.stm>.
Letter to the Editor:
Dear Editor:
It has come to my attention that students on our campus are not widely aware of the
threats invasive species as a whole face to our natural ecosystem. Certain species are
set out for the public to see, but it is too common for pests to be overlooked due to a
lack of education. One particular pest that is normally considered beneficial is the
common earthworm, suborder Lumbricidae.
These subterranean pests cycle organic matter back into the soil, which in the cases of
our natural forests is detrimental to the survival of the forests. The worms due to their
slow moving nature are unable to travel very quickly making them a non-problem, but
because humans can transport them hundreds of miles with little thought. It is essential
that we prevent the carrying of worms from location to location to preserve our natural
ecosystem. Awareness of the issue is essential in this.
Thank You,
Michael Wolenter & Aubrey Weibel
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