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Is The Redworm An Earthworm, Too? E-mail
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Sunday, 11 September 2005

by Stephen White & Zorba Frankel, from our issue #7

It is not the intention of Worm Digest to settle the controversy of whether or not redworms can/should be called earthworms. But we would like to bring some clarity to this issue so that when our editors talk about worms and their functions, our readers will understand what we mean. From one point of view it matters very little what you call something as long as you and the person(s) you are communicating with know what you are talking about and what "it" does. Let's see what we can do as a lay journal towards establishing some clarity for our readers. The question involves our friend the redworm, and whether or not it can rightly be called an earthworm. Two researchers, Matthew Werner and Uday Bhawalkar have brought to our attention different points of view regarding nomenclature for earthworms and redworms This discussion is certainly not restricted to these two men, but since the Worm Digest staff respect both and have and will continue to publish their works, they will serve as the point of departure for this discussion.

Matthew Werner, staff researcher in the Agroecology Program at the University of California, Santa Cruz has stated (Worm Digest #5, "Real Earthworms") that the redworm should be called an earthworm as it lives in the soil, albeit the "surface layer of fallen plant litter," which he considers a part of the soil. Due to this location of habitat for the redworm he refers to it as an epigeic species, but an earthworm nonetheless.

Uday Bhawalkar of the Bhawalkar Earthworm Research Institute, Pune, India, prefers not to call the redworm an earthworm due to their difference in functions. While the redworm has a role in feeding on the organically rich surface layer of the soil, it also serves as "nature's agent which quickly grows when excessive amounts of organic wastes are dumped on the soil. They help reduce this pollution by consuming it, producing their own biomass quickly and then migrate to die on other patches of soil." According to Bhawalkar, this process is nature's way of distributing the nutrients contained in the excess wastes over a wider area.

By comparison, Bhawalkar states that the earthworm is a burrower, a soil processor, "eating dead organics and rock particles, grinding and excreting them as a finely ground mix which serves as food for bacteria. They do not assimilate the organics, to the same extent as the redworms, for themselves." Thus their numbers do not multiply as quickly as do the redworms, whose assimilation rate is far greater. This high rate of assimilation means that the nutrients consumed by the redworms go into building their own biomass while the earthworm passes on these nutrients in
a soluble form in their castings.

Quoting from Werner's article "Earthworm Ecology for Farmers," (Worm Digest #5), "Earthworm feeding and burrowing activities incorporate organic residues and amendments into the soil. These behaviors enhance decomposition, humus formation, nutrient cycling and the development of soil structure. Earthworms increase the amount of nitrogen mineralized from soil organic matter. Nitrogen-fixing bacteria are found in the gut of earthworms and in earthworm casts, and higher nitrogenase activity, meaning greater rates of N-fixation, are found in casts when compared with soil." In addition, the increased ability of soils to absorb water and therefore drain better is also a known result of earthworms.

Now, if you wanted to improve a plot of soil by increasing the earthworm population therein, and someone sold you redworms for that purpose, I believe that both Werner and Bhawalkar would shake their heads, NO! No matter what you call it, it's not the right worm for that function. Simple and clear.

So what is Worm Digest's position on the redworm/earthworm question?

Worm Digest will refer to both redworms and the burrowing species as earthworms. We will also use the terms "redworm" and "burrowing earthworms" to refer to those worms specifically.
Last Updated ( Sunday, 18 September 2005 )
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