Jodi Johnson-Maynard is an assistant professor of soil and water quality at the University of Idaho. She is one of Idaho's experts on the giant Palouse earthworm.
Why did we pick this prairie remnant to dig for the giant Palouse earthworm?
This is a lovely prairie remnant here in the Palouse that belongs to the Jensen family. It’s in bloom right now, so it’s a lovely time to be up here and look at the wild flowers. And part of my research has focused on looking at the soil fauna in the prairie remnants to get a baseline of what is here. What’s underneath these prairies has been largely unknown, so ever since I’ve been here, I’ve worked on figuring that out.
This prairie remnant is estimated to exist only at a tenth of a percent of what was originally here. Most of it has been converted to agricultural lands for obvious reasons. I’ve heard it’s one of the most productive wheat producing dry land areas in the world.
We really don’t know much about how these prairie systems function on a biological scale, and so there has been a team of researchers who have taken on this research task and have been working on it the last four to five years.
What is so cool about the giant Palouse earthworm?
Driloleirus americanus is the Latin name. And its name comes in part from the fact that apparently it has a lily scent to it. I’m not sure about that, but it seems to be a defense mechanism. If the worm feels threatened it will actually secrete fluid that smells like lilies. So that’s one unique thing about it.
And it was described in the late 1890s and apparently it was quite common. There were several references in the early literature about it being commonly distributed across the Palouse and people would send in samples to Washington State University to have them described. And there were some papers in the early 1900s that also describe it as being pretty common in the environment.
There was an article in a local paper that had the giant Palouse earthworm on the front page, right underneath George Bush, as a matter of fact. And I thought, wow, this is great! This is a good day! People are paying attention to what’s underground because it’s so important. The biological diversity underground is so much greater than what we have above ground, and we really don’t know that much about what it is doing for us.
The biological diversity underground is so much greater than what we have above ground, and we really don’t know that much about what it is doing for us.
Why is it now scarce?
I think there are a couple different things. One is just the disturbance. This earthworm will actually spend most of its time fairly deep in the soil, but it has to come up to feed, and other earthworms that have a similar biology such as the night crawler, we just don’t find them in the agricultural fields around here. So I have sampled a lot of these fields that you are looking at out here. I’ve dug a lot of pits since I’ve been here, soil pits, and we just don’t find the night crawler or the giant Palouse in any disturbed areas. So that gives a chance for the European worms to come in and kind of take over where they can survive.
So, the decline of the worm is related to the rise of agriculture?
We don’t have very many data points, unfortunately. We have the findings in the late 1800s and the 1920s era, and then we have some sightings and some collections that occurred in the 1970s. And I’ve actually talked to the person who collected those specimens, so I know where they’ve come from across the Palouse. Some of those sites have very limited access now; some of them are completely destroyed now. It seems as if we don’t have the data to back this up, but it seems like a pretty good correlation between the onset of the farming, the intense agriculture regime here, and the decline of the native earthworm.
How would it compare to the invasive species, the night crawler, in size and length?
Some of the night crawlers can get to the same size around here. It just depends on what they are feeding on, what the environment level of disturbance is, those sorts of things. Predation by birds, if there are parasites in the soil that will kill them. So, as they age, they get bigger and approach the same size as the giant Palouse. The color is extremely distinctive, and that will easily set them apart. Other than that, we have to look under the microscope to look at some fairly specific morphology of the worm to detect what it is.
What does the giant Palouse earthworm eat?
It’s something that we can’t really trace very well. If you think about the night crawler, it will actually come to the surface and feed, and then carry the litter material back down into its burrows. So it may be that it has the same habit and that’s how it feeds, but really we don’t have any good detailed information on that.
What about the reports of earthworm burrows many feet underground?
I’ve had people tell me when they are digging for certain reasons or they are doing excavation for a building or a project, that they found burrows that will go fifteen, twenty feet down. It’s a little bit hard to really say how deep they can go, just because the soils here have been built up, layer on top of layer, of different episodes of loess deposition, windblown material being deposited; and so it’s a little bit hard to say, because some of those burrows could actually be relics.
They line the burrows with a mucous layer so they’re a fairly stable feature, and then you have this newer episode of loess deposition on top of that which becomes the modern surface, so it’s a little bit hard to tell for sure exactly how deep some of their burrows would extend. But I have no trouble believing they might go easily five, six feet down into the soil.
What do the worms do for the Palouse soil?
Earthworms in general are very good at aerating the soil. If they’re the type of worm that comes to the surface to feed, they’re actually making large pores in the soil, and that really helps water to infiltrate, and we like that. We like that a lot, because when you don’t have good infiltration, you tend to have a lot of run-off, and when you have run-off, you tend to have erosion.
So they can help prevent erosion by creating those channels and allowing better infiltration. It also allows air, oxygen to diffuse into the soil fairly readily, so that the plant roots will get the oxygen that they need.
They are very important in nutrient cycling. So they come to the surface perhaps and feed on this litter material you see here – the thatch layer – and they just physically break it down into very small pieces; and when that is in the earthworm’s gut, it’s constantly being mixed up with microbes and soil, so you have a good environment there for decomposition of the litter material, and that releases nutrients back into the soil.
Do you have any difficulty defending your interest in earthworms?
I think we have to appreciate the organisms. Most of the creatures on this earth, it seems like they do play an important role in the web of life in some way; and earthworms definitely add to the fertility of the soil. So just from that fact, if you look at nitrogen fertilizer costs, they’re going up, so earthworms have been called "nature’s tillers" because they’re constantly mixing this organic material, nutrient rich material into the soil. So they do provide a really important function in natural environments.
In agricultural fields we sometimes have to replace their natural functions with other artificial means, like fertilizer and aeration activities. People are recognizing more and more that a healthy earthworm population can really move us a long way on that scale to becoming more sustainable.