Invasive Crazy Snakeworms
Program Review: Earthworms: Good and Bad by Dr. Josef Görres
February 25th by Victoria Weber and Beth Gutwin
Vermont has no native earthworms as they were all wiped out by glaciers. About 300 years ago European earthworms were introduced to North America in soil ballast of ships. Then about 80 years ago Asian earthworms began arriving in the United States, appearing in Vermont 20 years ago. So far 19 species of earthworms have been identified in the state, 4 of which are Asian and at least 2 of those are aggressive enough to be termed invasive, that is, they disrupt natural ecosystems. Once you find the Asian earthworms, you typically don’t find European earthworms any longer.
Dr. Josef Görres, who teaches soil science at UVM, began by praising the benefits of earthworms. Vermicompost, compost created by red wiggler worms, Eisenia foetida, is an excellent fertilizer, but it is hot (very nutrient rich) and too salty and should not be used at a concentration greater than 10% by weight for potting mix. Red wigglers can be identified by their yellow tails and vertical stripes between the segments along their bodies if you stretch them out. Red Wigglers don’t survive well in your gardens or in the forests as they require a lot organic matter. Unfortunately, most companies that sell ‘red wigglers’ do not do a good job differentiating between species so that there are almost always other species mixed in with red wigglers that you might buy. The farther south a worm supply company is, the greater the chance of getting invasive snake worms in any purchase.
Crazy Snakeworms
A relative newcomer from Japan and the Korean Peninsula is the “Crazy Snakeworm” (Amynthas agrestis, Amynthas tokioensis and Amynthas hilgendorfi), or “Jumper Worm”. The nickname refers to their energetic thrashing about if disturbed, to the point where they seem to ‘jump’ out of your hand if you are holding them (hence ‘jumper worm’). They can flay about so energetically that if a gardener or bird grabs one end, the tail can break off and the front end can slither off, giving the worm a 50% chance of escaping. The ‘snake’ part of the name has to do with their method of locomotion, which is a side-to-side slither, like a snake, and unlike most earthworms’ lengthwise expanding and contracting movements.
In Vermont, Amynthas spp. have been found in deciduous and mixed deciduous-coniferous forests, compost, mulched beds, ornamental beds amended with municipal leaf litter waste, plant containers and gardens. This earthworm is extremely invasive and considered a forest pest, although few states officially recognize it as invasive. This earthworm is often spread via field and container stock from nurseries, by gardeners sharing plants, and from left-over fishing bait, and potentially in commercial mulch and compost as well. Amynthas spp. are capable of rapid destruction of horticultural crops, including hosta and lady’s slippers (see NYT article: http://www.nytimes.com/2007/03/15/garden/15nature.html), and remarkably rapid decomposition of woody mulches.
There are three earthworm ecotypes:
· Anecic earthworms make very deep, 6’ to 10’ vertical burrows. They pull plant material down into their burrows to eat and can construct little tents of sticks and other materials over the entry holes, called middens. The only species known to us in New England is Lumbricus terrestris (“nightcrawler”) which is pigmented on its top side and head.
· Endogeic earthworms live underground in the top 10” of the soil, feeding on microorganisms and fungi in the mineral soil layer. These worms are unpigmented, with transparent pink, green and grey hues, and are the composting worms.
· Epigeic earthworms inhabit the soil surface in the resource-rich part of ecosystem, e.g. forest leaf litter, mulch and thatch. These worms tend to be pigmented, can get sunburned, and include red wigglers and snakeworms.
·
Characteristics of snakeworms
Snakeworms inhabit the top 5-10 cm (2”-4”) of soil and are often found immediately under mulch or duff, on top of the mineral soil. They are ‘annuals’ and grow to 6” to 8” long. They appear denser, almost hard, compared with ‘regular’ earthworms; some have a bluish sheen, like oil on water. When touched, a snakeworm will thrash about, whereas a nightcrawler will flatten its tail if its nose is touched. Snakeworms also have a more turgid and muscular appearance than nightcrawlers, because they retain high levels of salt as protection against predators. The apparent muscularity is a product of the hydrostatic pressure associated with their salt level, not actual muscularity.
Once they are mature, probably by June (although it varies with moisture levels and heat), Amynthas earthworms have a whitish band called a clitellum going all around their body toward the head end. This is where the eggs are produced. The band comes off over the worm’s head, the ends close and it becomes a tiny black dimpled casing called a ‘cocoon’ which has 1-2 eggs inside. Each worm can create about 60 of these cocoons in a season. The eggs overwinter, unfazed by temperatures of -40° F or colder, while the worms die of cold by Christmas time. In the Hort Farm woodlands, Görres has found 2,000 egg cocoons per square meter of soil.
Other things that Dr. Görres’ research has found is that snakeworms can travel/ expand their territory 30 to 40 yards in a year, and they are most likely to move downhill. A few worms have been found to have an unnamed protozoa which seems to be having a negative effect on the worms – a possible bio-control. Snakeworms have been found in every county in Vermont except the North East Kingdom, Orleans and Essex, with highest numbers in Windsor and Chittenden counties.
Seasons
European earthworms – the ones we used to think of as very useful in our gardens – are active in spring and fall and go dormant in July and August when it is too hot and dry. Snakeworms go full blast in summer, laying eggs from July through November. Snakeworms mature faster, and begin to lay eggs earlier, if the temperatures are warm and there is plenty of moisture.
Forests
Invasive earthworms possess the ability to change ecosystems, especially those of forests. They can alter forest soil structure to the extent that it can no longer support germination of trees and understory plants, which may lead to woodland thinning, slower canopy regeneration due to deer browsing the remaining plants, and increased vulnerability of ground-nesting birds to predators. Ephemeral wildflowers are negatively affected. The worms’ castings look like coffee grounds and there are often thick layers of these just under the top layer of duff, or on the soil surface. Seeds cannot get a purchase or keep moist enough to germinate. Established plants die not from snake worms feeding on their roots, but from the roots’ exposure to air as a consequence of soil disturbance and the loose layer of castings. A phenomena called ‘tree gingivitis’ occurs when so much duff and soil is eaten that soil levels go down significantly, leaving plants’ crowns and roots exposed to the air and dryness by receding soil.
Mycorrhizae of fungi seem to be disrupted, which in turn can affect the trees and other plants that the fungi help support. Ferns seem to be one type of plant that are not negatively affected by snakeworms. Jack-in-the-pulpit may be indicators of earthworm invasion. With many fewer herbaceous plants growing, deer eat more young sugar maples, affecting maple regeneration and, long-term, the maple sugar industry. Also, the soil disturbance caused by the worms, and the lack of competition from other plants, can increase invasive plants in forests, which also puts more deer pressure on young maples.
Heavy metals
Snakeworms bio-accumulate 80% of the amounts of airborne heavy metals deposited in our soils and forest floors from Midwest industrial sources, as well as toxic trace metals. This could pose a problem for human health if chickens and other animals consume the worms and pass the metals on in their eggs or meat. It can also pose a problem for wild birds and other wildlife that might ingest snakeworms.
Control
Snakeworms reproduce rapidly, and they have no known predator, except perhaps geckos. They die after frost, but egg casings survive the winter. The best time for elimination is early to mid-June, after eggs have hatched but before worms begin laying eggs, with a second treatment in August or September.
Early Bird
There are no pesticides or proven biological control measures available for use against earthworms. However, one product which has shown some promise against snakeworms is “Early Bird” (as in “gets the worm”!) by Ocean Organics of Waldboro, ME. It is marketed as a 3-0-1 fertilizer. Developed for the golf course industry, it contains chicken droppings, kelp and oil from seeds of the tea plant, Camellia sinensis, the tea we drink. Saponins in the tea seed oil have a soapy quality, and are irritants to earthworms, causing them to come to the surface, where they die. Dr. Görres has seen worms come up out of the soil 10 minutes after an application of Early Bird, and in 20 minutes they are dead. Görres diluted the liquid Early Bird 20 times. The salesman suggests 25 to 75 times. Clearly some trials need to be done to clarify what works best using the least amount of Early Bird. Saponins may be harmful to fish if they reach water bodies in high concentration. It is not known if Early Bird affects other soil animals.
The safest way to use Early Bird is probably not in applying it directly to the soil, but to new plants that you may be bringing into your garden. Drench the pots with Early Bird and wait for it to take effect before you set new plants out in your garden. If you do drench the soil, try to judge how deeply it goes, and keep it in the top 6 “ or so to avoid hurting European earthworms.
Other means of prevention
A mustard solution of 1 oz. (1/3 cup) powdered mustard seed (the spice) per gallon of water has also been shown to be effective as a drench to bring worms out of the soil. You may then need to drown them.
It is possible that finely ground biochar kills these earthworms. A small amount of biochar added to the soil may be enough. The sharp edges of biochar particles disrupt the earthworm guts when ingested. This may be an alternative to mustard or Early Bird. It is likely that this amendment will be tested this summer.
Prevention is key
To avoid acquiring snake worms, Dr. Görres recommends remaining vigilant, keeping municipal mulches and composts out of your garden, and checking plants and containers you acquire from nurseries or fellow gardeners. Consider using compost tea, rather than compost itself.
Plants that have been in the ground or in pots sitting on the ground for some time at a nursery are more likely to have snakeworms in their soil, if the worms are present at the nursery. In the northeastern USA, snakeworms were first identified in greenhouses and other horticultural settings in the 1940ties but not in the wild till much later towards the end of the last century. Indeed, snakeworms thrive in horticultural settings where mulch may feed their appetite and irrigation keeps them moist even during a drought. Raised beds with the additional temperature benefit seems to encourage them as well.
The following is a link to an informative fact sheet by Dr. Görres titled Invasive Earthworms in the Northeastern USA and the Horticulture Industry at
Another is Earthworms in Forests by UVM and the Vermont department of Forests, Parks and Recreation, at http://fpr.vermont.gov/sites/fpr/files/Forest_and_Forestry/Forest_Health/Library/EarthwormsInForests_final.pdf
Thanks to Robin Worn and Mary Jo Childs for contributing to this report.
Review
of Josef
Görres’
March
2019 talk
“What
is New
in Snake
Wormology?”
by Victoria Weber
and Josef Görres
Snakeworms
are voracious. They eat a lot and
they create a lot of castings which negatively affect forest ecosystems. More on that in a minute.
Snakeworms
are annuals. They hatch in spring
and grow from tiny (the size of a saffron strand, about 2/3 of an inch) to
pencil thickness and 3” to 7” long over one summer. The juvenile already
thrashes like an adult when you pick it and place it in your hand. They need 3
months of above-freezing temperatures to mature and make eggs which carry on
after they die in fall and early winter frosts -- just like a lot of annual
weeds. Those eggs are contained in
little capsules or egg casings called cocoons. These capsules hold one or two eggs and can withstand dry
conditions and temperatures of
-40° C [= -40° F]. Indeed, they survive cold by
desiccating so that ice crystals do not form in their cells.
Snakeworms are bad
But
wait! Aren’t earthworms good? Don’t they aerate soil, and make lovely
castings that can be used as fertilizer?
Think of all those drawings and animations of friendly earthworms with
enormous round eyes and a smile like a stamp of environmental political
correctness, and don’t we have an involuntary positive reaction to these
drawings? A little tilting
forward, maybe a little smile?
Don’t these cute worm drawings usually entreat young children to do
something positive for the environment?
So we have been taught from our earliest years that earthworms are good
guys.
You
may be saying: And now you are telling me
that some earthworms are NOT a good guys!?! Come on! And by the way, I am sick and tired of one negative thing
after another damaging or threatening our forests, gardens and landscape.
People
really do not want one more bad thing.
The
problem is that with invasives one bad thing almost always leads to more and
worse bad things. Like the potential
collapse of our New England forests, including our maple sugar bushes, the wild
orchards that Vermonters ‘tap’ early each spring to 1) keep from going crazy,
2) produce something sweet, and 3) pay the taxes.
What snakeworms do:
They
eat a lot and they out-compete other species.
 |
| Camel’s Hump forest without snakeworms (left) + a Vermont forest with snake worms |
Most earthworms live a ways
down in the soil. Snakeworms
hang out in the top few inches of the soil and just under the mulch or leaf
layer onf the
soil. Snakeworms eat any
debris, mulch, forest duff layers, dead leaves, soil, wood debris. They really
don’t care what they feed on! Then they poop out ‘castings’ which accumulate on
or just beneath the forest floor surface. This layer is typically 5 -10 cm (2-4
inches) thick. The castings look
like coffee grounds. They
are small black crumbles. These castings do not clump together and
wick moisture. Instead they form a
loose, dry layer up to several inches thick on top of the soil. Seeds of trees or herbaceous ground
cover plants that fall on this layer do not sprout at all, or if they
do, their rootlets cannot get
down to the soil layer with moisture and the density to anchor them. Seedlings that do survive may become browse for deer. The upshot of this is that forest canopy trees do not regenerate.
Scientists
can determine how long snakeworms have been in an area by determining the age
of the youngest saplings. There are almost no new saplings after
snakeworms have moved in. One
study in a Vermont sugar bush found .5 saplings per square meter in areas with
snakeworms, and 6 saplings /sq.m in areas without snakeworms. Think 40 years ahead and imagine how
the maple sugar industry will be doing.
Additionally,
by eating the same foods that small animals such as millipedes eat, snakeworms
out compete them, and they starve to death. Hence a yet-unknown amount of the microscopic and
small life in the forest floor is eliminated or much reduced.
It
should be noted that other earthworms also damage forest ecosystems with their,
less dense, castings. Snakeworms
usually outcompete other species of earthworms and they disappear.
Where do we find them?
Initially snake worms are usually introduced
horticulturally via new plants in pots or fabric root balls, as well as in mulch, compost, wood chips, mulch or top soil. They are most often located in raised
beds, mulched beds, and flower beds with leaf mulch. They eat any mulch layer at an alarming rate and if you find
that your mulch layer is not lasting very long, perhaps disappearing within one
season, it is likely you have snakeworms. The casting layer will also give them away.
|
Many
otherwise beneficial horticultural practices that are getting more recognition
feed and move snake worms. For example, Municipal initiatives to gather raked- up
autumn leaves, take them to transfer stations, make compost and sell or give it
to individuals or nurseries, while well intended, can and do spread snakeworms
and their egg cocoons.
Compost
piles support and later spread snakeworms. If the temperature gets up to 140° F both snakeworms and
their cocoons can be killed, but – especially in Vermont – this is much warmer
than most of our compost piles get. Even if the high temperatures of 130℉ are reached at the center of the compost pile or windrow, the worms will move to the outside of the compost where it tends to be
cooler.
cooler.
Vermiculture
is a business and many purveyors do not recognize snakeworms, admit that they
may be a problem, or have any means of keeping them out of their worm
stock. Hence all or some of the
worms you buy for composting may include snakeworms.
Snakeworms
are also sold as fishing bait. The
thrashing, active behavior is thought to draw the worm to the attention of
fish. Areas around lakes or
streams where fishing is practiced often have significant snakeworm
populations. This is true near
Silver Lake in Barnard, VT.
Who are they and where do they come from?
In
North America there are 172 earthworm species. In areas that were glaciated, all earthworms were wiped out
and then repopulated by European species from ship ballast.
South of glaciated areas,
there may be native earthworms. Currently in North America 1/3 of earthworms are exotic/alien and
1/10 are pheretimoids, which is the group of Asian earthworms that includes
snakeworms. All snakeworms are
pheretimoides, but not all pheretimoides are snakeworms.
Thirty-seven
states reported having snakeworms as of 2018. In the northeast we have 3 species of snakeworms: Amynthas
tokioensis, Amynthas agrestis and Metaphor hilgendorfi. The
snakeworms we have in Vermont are from Japan and Korea, and they exist in China
and Taiwan as well.
New
York state and Wisconsin recognize snakeworms as invasives. See: https://dnr.wi.gov/topic/invasives/fact/jumpingworm/index.html
They
are generalists and are extremely adaptable (common characteristics of invasive
organisms). They can adapt to
their environment very quickly.
They have great ‘plasticity’ meaning they can adjust to things like temperature and food variation. They
are not specialized to eat one thing, and indeed by eating what other, more
specialized, invertebrates usually eat, they out-compete them.
Sex
Snakeworms
are parthenogenetic, which means they don’t have sex, but reproduce by asexual
reproduction in which offspring develop from unfertilized eggs. Theoretically this means they are all
clones, but they are not, and there are lots of genotypes in Vermont – they are really, really diverse.
There are several hypotheses on the reason for this, including maybe
they do have sex and no one has seen it yet, but 70-80% have no male sex
organs. 2-3% have both male and
female sex organs and are equipped for sex. More research is needed to find the
source of the genetic variation.
In
any event, after they are about 90 days old, they are sexually mature. At that point the clitellum, a gelatinous
sheath that surrounds their body, gets denser and begins to
move toward the head where it comes off – kind of like taking a sweater off –
and it contains 1-2 eggs. It is
now called a cocoon.
In
forest plots in Vermont, Görres and his students have found 500 to 1,500 cocoons
per square meter of forest soil. Thus
soils have ‘cocoon banks’ just like seed banks. They remain viable for at
least 2 years. Eggs hatch anytime
the temperature is 50°
F or above. With climate change,
growing seasons are lengthening, especially at the spring end, so snakeworms
are hatching earlier in the year, and having more time to create more eggs.
Strategy
There
is not a lot we can do about the cocoons, so emphasis is on avoiding or reducing the worms themselves. Treating
them before June,
when
they begin to produce cocoons, is the best recommendation. If we can kill or reduce the number of
worms by early June, that generation will not leave egg cocoons, and if we can
repeat for 5 years, the population should be knocked down substantially.
Controlling Snakeworms
Research
is really just beginning on this topic, and Professor Görres and his research
assistants have learned quite a lot in the past couple of years.
They need our help with data on damage and with funding so they can
continue researching. More on this
below.
The
controls that have been identified so far are saponins (soapy chemicals), a
fungus, and things that physically irritate their skins or their guts. So far, we
have the following:
 |
Saponin treatments
A
golf course fertilizer has been designed to kill earthworms, which are not
appreciated on golf courses.
It contains a 1-1-1 fertilizer and oil from the seeds of tea shrubs (Camilla sinensis) which is a
saponin. Diluted and poured onto
flowerpots or the soil, it irritates all earthworms, and they come up and
die. The product is called Early Bird (as in ‘…gets the worm’).
A
woman in Poughkeepsie NY named Jean Campbell thought of other plants that
contain saponins, focusing on alfalfa.
She spread horse feed in the form of alfalfa pellets and it had some
efficacy. Powdered alfalfa
does NOT seem to work, so get the pelleted variety.
Other controls
By
finding recently dead or dying snakeworms and cutting them open to try to see
what had killed them, researchers have isolated several microbial agents that seem to be effective. These are not commercially available. However a fungus called Bavaria Bassiana (which is on sale as BotaniGard) also has been shown to be effective in greenhouse trials.
B. Bassiana works
for cabbage worms, fly maggots and other insects. It controls insects by growing on them, secreting enzymes
that weaken the insect’s outer coat and getting inside the insect and
continuing to grow, eventually killing the infected pest. Görres’ graduate student’s trials shows
it does have some effect on snakeworms in a – two week time frame. EPA has factsheets on it. Bassiana may work on about a quarter of the cocoons as well
as the worms themselves.
Irritating the skin is another approach. Mustard seed powder – the spice you put in salad dressing – can be used at a rate of 1 oz. per gallon of water. Pour on soil. It irritates the skin and kills the worms. You can buy it in bulk at natural food stores or herbal companies online.
Biochar is similar to charcoal – wood
cooked or smoldered at low temperatures and low oxygen so that it does not
combust. If made from hardwood it
may be sharp enough to irritate the snakeworms’ guts and/or skins and reduce
the population. It takes time, at least 16 days, for this to work.
Really
sharp sand may work in a similar manner.
Diatomaceous earth, however, does not work.
What you can do
2- Do a little mental
adjustment. Accept that some
earthworms are bad for our ecosystems, especially our forests, and that this is
one more invasive organism that – even if it is depressing – we need to educate
ourselves about and work on.
3- Do a little more mental
adjustment to reconcile the good work being done on soil now, the general
feeling that soil should never be bare, but should have a mulch layer, with the
reality that that can encourage snakeworms. This is paradoxical and frustrating and needs to be
addressed.
4- Talk about snakeworms with
friends and your plant suppliers.
Let nurseries and garden centers know that you realize that snakeworms
are in our area and they are spread mostly via the horticultural industry. Help these suppliers recognize the
issue and the worms, and take action to keep their stock from being infested.
Some nurseries and farmers that are being impacted are avoiding seeking help as
they do not want to be stigmatized with having snakeworms. This is short-sighted and only
increases the problem and the infestation.
Encourage
horticulturalists to come out about snakeworms. Be compassionate, not accusatory. Help them set up good practices. Gorres is trying to get funding to develop good and safe practices. This is another reason why he needs help with funding.
5- Be VERY careful sharing
plants. Take the step to hose all
the soil off (into a safe container??) any plants you share with others or
bring into your gardens. A plant
is only safe if it is bare-root.
Plant sales and exchanges should be avoided unless you can bare-root the
plants before you get home. Alternatively drench plants in pots with Early Bird or diluted mustard seed powder to irritate any worms and cause them to exit before you move the pots.
6- Avoid bringing in mulch,
wood chips (how they got into my gardens), compost or other materials that can
harbor egg cocoons or worms.
7-
If you find you
have snakeworms, work on your own land and gardens. Treat worms in the spring
to try to knock down the population of this year’s worms BEFORE they begin
laying egg cocoons. Try to stop
the cycle of more cocoons which will persist in the soil for 2 years.
8- Data is needed to identify
where snakeworms are and to document damage they have done. There is a story of a hosta nursery in
Pennsylvania that lost 1/3 to ½ of its 30,000 plants due to snakeworms, but
stories like this need to be substantiated. Send photos of snakeworms to imapinvasives.org,
inaturalist.org and vtinvasives.org. Görres intends to create a specific place within
the Vermont invasives website for snake worms. He will send a link and instruction on how to use it to the Hardy Plant Club list-serve, probably in April 2019. Look for it and add information to it.
9- If you are a stakeholder,
especially a commercial operation, file damage reports with specific information
(and photos if possible) on which plants are impacted. Was it plants in pots or in-ground
production? In greenhouses,
tunnels or outside? What
symptoms? Try to put a realistic
cost on the damage. Send the report to jgorres@uvm.edu People
are used to believing earthworms are good for plants and soil. Help explain to people what damage you
have witnessed. Begin to change
the cultural attitude.
10- Be a collaborator. Help the overall effort to study and
identify controls. Professor Görres is looking for someone who is willing to put their plants
on the line and help with experiments. Contact him at
UVM Department of Plant and Soil Science, Josef.Gorres@uvm.edu (401-743-4311).
11- Dr. Gorres is looking for funders. If you have any leads, or if you could donate yourself, please let him know. So far funding has come from private groups, including the Hardy Plant Club of Northern Vermont. Government funders do not seem convinced there is problem. This is why documenting negative effects of snake worms on the invasive web sites mentioned is so important. So is collaborating with Gorres in his Research.
n Victoria Weber, March 2019.
Weber has been working on and with invasive plants for 23 years
so far. The longer she does, the
more she recognizes that our attitudes toward invasives areis
key to how we go about dealing with them, and IF we are willing to take
action. She encourages people to
try to sort out their feelings and attitudes so they can work effectively
without becoming overwhelmed. She
believes in ‘planned persistence’ to work steadily over a long period of time
to make a lasting difference.
wdimock@sover.net
