Earthworms & the mechanical functions they perform in the soil

File under - "Lost and Found"

Colorado State Agricultural  eXtension

Here are some quotes and the link from the Colorado State Agricultural Extension on the three types of earthworms and how to encourage them and dangers that destroy their ecosystem.

How to Encourage Earthworm Activity

"Earthworms will not go where it is too hot/cold or too dry/wet. Soil temperatures above 70ºF or below 40ºF will discourage earthworm activity. While soil temperature is hard to alter, moisture can be managed. When soil becomes water logged, oxygen is driven out of the large pore spaces. Without this free oxygen, earthworms cannot breath. Conversely, when soil dries beyond half of field capacity, earthworm skin dries in the soil. Maintaining moisture levels that are ideal for optimum plant growth in a landscape or garden will also be ideal for earthworm activity.  Providing a food source in the form of organic matter is also important. Mulching grass clippings into the lawn, putting down a layer of organic mulch in beds, amending the soil with compost, and turning under a green manure are all excellent ways to feed earthworm populations."

Practices Detrimental to Earthworm Activity

"High rates of ammonium nitrate are harmful to earthworms  (most common lawn fertilizer used in pellet form)

Tillage destroys permanent burrows and can cut and kill worms. 

Fall tillage can be especially destructive to earthworm populations. 

Deep and frequent tillage can reduce earthworm populations by as much as 90%. 

Earthworms are also hindered by salty conditions in the soil. 

Some chemicals have toxic effects on earthworm populations.

(Source)

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In most discussions of earthworms, there are always three major types referred to with several species referenced within these kinds of earthworms. Yet there are far more like the common red earthworm otherwise known as a compost worm which I've most often found in the rich manure layers around farms. Actually I also found them around the organic layers where my gray water pipe emptied into the ditch up in the mountains where I once lived because much of the vegetable matter which went through the kitchen garbage disposal. 

Epigeic Earthworms (surface litter dewellers)

Of course the result in performing the aeration program is that the grasses in the lawn will perform better until it needs to be done again, which in many cases may be a yearly event. Another very important point in that graphic is the first picture which illustrates the tightly bound soil and grass roots with a compacted thatch build up of dead grass blades, roots and stems. In nature this thatch buildup would have been regularly handled by the abundant microbes available and the other earthworms like the "Epigeic" species which are surface dwellers and litter feeders and make no underground burrows. Nevertheless, this thatching done mechanically is yet another chore that must be done periodically when unnatural synthetic versions of maintenance programs on lawns are undertaken, then all that waste once accumulated must be hauled off to a green waste landfill where they compost it. 

image: Earthworm Society of Britain (Epigeic Earthworm)

It wouldn't surprise me if these were the types of earthworms we most commonly see when we turn over rocks, bricks and boards. Of course they generally are never alone. Sow Bugs, earwigs, mites, ants etc etc etc all contribute to the soil health. Why ? Because they all feed one way or another on organic matter and poop out nutrients available to plants their either direct root contact or the mycorrhizal fungal grid. I have to imagine that when all gardeners, including myself, dig through the soils, we've all stumbled upon all three varieties of earthworm types, but never gave their differences a thought. Earthworms are just Earthworms right ? Wrong! That's almost as bad as UC Davis', Alison Van Eenennaam justifying GMO technology by saying, "DNA is just DNA and Genes are just Genes." I can understand the average person saying this, but not one of the world's well known Sciencey celebrity intellects self-promoting themselves as having an understanding well above the average *cough-cough* Layman (hate that put down term).

image: Earthworm Society of Britain (Endogeic earthworm)

Both types of burrow dwelling earthworms shred residues, stimulate the microbial decomposition and nutrient release. They both produce casts rich in N, P, K, and other nutrients. Improve soil stability, air porosity and moisture holding capacity by burrowing and aggregating soil. Turn soil over and may reduce the incidence of disease by bringing deeper soil to the surface and burying organic matter. They improve water percolation and infiltration by forming channels and promoting soil aggregation and stimulate root growth by creating channels lined with nutrients for plant roots to follow. Both endogeic and anecic earthworms are important mechanical components in contributing to these incredible soil infrastructure functions in all soil ecosystems. The shallow dwelling earthworms improve topsoil porosity and the deep burrowing earthworms improve infiltration and drainage, often times up to several feet depending on the soil and species. It's this soil breathing function they provide through aeration that is most important. Prior to the much celebrated 1950s "green revolution", those nitrogen poor soils always seemed to have plenty to offer plants. Why ? because out atmosphere is loaded with it and if the soil breathes properly, then the nitrogen fixing microbes can do their work effectively on the plant's root systems. But the advent of the Synthetic-Artificial Ag revolution changed all that and caused the beginning of the end in what nature was programmed to do for 10s of 1000s of years prior. 

Anecic Earthworms (Deepest Burrowers)

Cornell University Soil and Water Laboratory

This is a great page create by Cornell University's Soil & Water Laboratory on the flow dynamics of water infiltration and percolation down into the soils by various mechanical components. This pit or trench which was dug into the soil for the study was approximately a meter in depth. There were a number of reasons for the ability of water to percolate and infiltrate deep into the soil, like the usual cracks in soils, the soil structure itself wwhether sand, clay or stoney soils, and finally the real intriguing feature were the deep vertical pore tunneling done by earthworms. In particular these Anecic types of Earthworms like, Nightcrawlers or Dew Worm (Lumbricus terrestris), which I use to collect in the dark at an old Iowa Farm in Buchanan County where the perennials had grown back covering the once barren barnyard. This photo at right shows how the "pore generators" or Anecic Earthworms which bore vertical straight line burrows may go down deep into the soils. Unlike the other varieties which burrow near the surface and around organic litter, then prefer the subsoil. That's good because that allow deeper percolation and infiltration of rainwater beyond the black biologically rich surface soils when it comes. 

image: Earthworm Society of Britain (Anecic earthworm)

One wonders what roles millions of these played in the past as to groundwater infiltration within an old growth ecosystem whether forest, prairie, chaparral, etc. Their presence would have also benefited certain plants which drill deep into soils several meters deep like the prairie perennials of historical times past. There are so many ecosystems so damaged or completely destroyed and extinct, that we may never truly be able to understand the potential for good within these systems that such living and moving biological components contributed to pristine soil health. Check out this excellent video called - "Bioturbation - Worms at Work" which shows three different species of earthworms working together in breaking down organic matter and tunneling within their respective niche habitats under the ground. This all takes place over the time frame period of a month. 

To finish off here, I'll post several large species of earthworms from around the world and even North America which are either now limited or extinct in traditional locations when land mismanagement has destroyed old growth habitats where these giants haven't been seen since the 1960s/70s. Like the megafauna of old which thrived and dwelt in old growth ecosystems, it's the larger organisms which seem to suffer harm first.

Giant Gippsland Earthworm

photo credit: http://homepages.rootsweb.ancestry.com/~aherns/worms.jpg

Common Name: Giant Gippsland Earthworm, (Megascolides australis). The Giant Gippsland Earthworm is found in Gippsland in south-eastern Australia, burrowing in the soil where there is lots of water to help them breathe. These burrows can be right at the surface to over a meter (over 3 feet) deep. The earthworm can stretch to over 3 meters (10 feet). Questions, what function and purpose to they serve in their specific ecosystem ? They are mostly extinct from their former range in Australia with the exception of a few locations, but should we care ? Such questions believe it or not in this enlightened day and age where we ask about "function" and "purpose" are often times viewed as dirty words to many obsessed with worldview, but they still have to be asked.

The Giant Palouse Earthworm of (Washington/Idaho)

"The giant Palouse earthworm, a big white worm native to the Palouse prairie region of Idaho and Washington state, was said to be abundant in the late 19th century — then seemed to disappear." 

Like other fascinating rediscoveries of large earthworms last seen in Oregon and Northern California which were last seen in the 1960s/70s, this interesting earthworm is causing some concern and the question is why ? As usual, Farmers are up in arms over the discovery. Viewing it as a threat to their livelihood instead of a soil asset, here is what was quoted by upset Idaho farmers in an NPR article on the exciting discovery:

"There's great potential for loss of freedom of what you can do with your land if the government comes in and says, 'Well, you have to do such and such, or you can't do such and such because we have to protect the giant Palouse earthworm.'

(Source)

These worms can apparently go down 15+ feet into the soils with their burrows. Why would a farmer consider this a disadvantage ? Especially with proven practices of No-Till systems and perennial cover crops which build up rather than destroy soil biology. It's a type of mentality of resisting change which would actually increase profits, not endanger an entire livelihood. But the old accusations of the country is turning Socialist and "My Granddad did things this way for generations and by-god I'll be doing the same till I die" are the usual chants one hears now days. You can bet the agro-chemical and biotech corporations will also make sure they'll keep that mindset too.

Important Reference Links

http://www.ext.colostate.edu/mg/gardennotes/218.html

http://soilandwater.bee.cornell.edu/Research/pfweb/educators/intro/macroflow.htm

http://www.earthwormsoc.org.uk/earthworm-information/earthworm-information-page-2

NPR: Scientists Capture Elusive Giant Palouse Earthworm

From AccuWeather.com: Why do earthworms surface after a rainstorm ?

http://www.accuweather.com/en/weather-news/why-do-earthworms-surface-afte/28916

USDA: "Agricultural Management Effects on Earthworm Populations"

http://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs142p2_053291.pdf