Earthworms (Annelida:

Oligochaeta) of the

Columbia River Basin

Assessment Area

Sam James

United States

Department of

Agriculture

Forest Service

Pacific Northwest

Research Station

United States

Department of the

Interior

Bureau of Land

Management

General Technical 

Report

PNW-GTR-491

June 2000
Author

Sam James is an Associate Professor, Department of Life Sciences, Maharishi University of

Management, Fairfield, IA 52557-1056.
Earthworms (Annelida: Oligochaeta) of the

Columbia River Basin Assessment Area 

Sam James

Interior Columbia Basin Ecosystem Management

Project: Scientific Assessment

Thomas M. Quigley, Editor

U.S. Department of Agriculture

Forest Service

Pacific Northwest Research Station

Portland, Oregon

General Technical Report PNW-GTR-491

June 2000
Preface

The Interior Columbia Basin Ecosystem Management Project was initiated by the USDA Forest

Service and the USDI Bureau of Land Management to respond to several critical issues including,

but not limited to, forest and rangeland health, anadromous fish concerns, terrestrial species viability

concerns, and the recent decline in traditional commodity flows. The charter given to the project was

to develop a scientifically sound, ecosystem-based strategy for managing the lands of the interior

Columbia River basin administered by the USDA Forest Service and the USDI Bureau of Land

Management. The Science Integration Team was organized to develop a framework for ecosystem

management, an assessment of the socioeconomic biophysical systems in the basin, and an evaluation of alternative management strategies. This paper is one in a series of papers developed as background material for the framework, assessment, or evaluation of alternatives. It provides more detail

than was possible to disclose directly in the primary documents.

The Science Integration Team, although organized functionally, worked hard at integrating the

approaches, analyses, and conclusions. It is the collective effort of team members that provides

depth and understanding to the work of the project. The Science Integration Team leadership included

deputy team leaders Russel Graham and Sylvia Arbelbide; landscape ecology—Wendel Hann, Paul

Hessburg, and Mark Jensen; aquatic—Jim Sedell, Kris Lee, Danny Lee, Jack Williams, Lynn Decker;

economics—Richard Haynes, Amy Horne, and Nick Reyna; social science—Jim Burchfield, Steve

McCool, and Jon Bumstead; terrestrial—Bruce Marcot, Kurt Nelson, John Lehmkuhl, Richard

Holthausen, and Randy Hickenbottom; spatial analysis—Becky Gravenmier, John Steffenson, and

Andy Wilson.

Thomas M. Quigley

Editor

United States

Department of

Agriculture

Forest Service

United States

Department of

the Interior

Bureau of Land

Management

Interior Columbia Basin

Ecosystem Management

Project
Abstract

James, Sam. 2000. Earthworms (Annelida: Oligochaeta) of the Columbia River basin assessment area.

Gen. Tech. Rep. PNW-GTR-491. Portland, OR: U.S. Department of Agriculture, Forest Service,

Pacific Northwest Research Station. 13 p.

Earthworms are key components of many terrestrial ecosystems; however, little is known of their

ecology, distribution, and taxonomy in the eastern interior Columbia River basin assessment area

(hereafter referred to as the basin assessment area). This report summarizes the main issues about

the ecology of earthworms and their impact on the physical and chemical status of the soil. The

three main ecological types of earthworms found in the basin assessment area are epigeic, endogeic, and anecic. Each type has a different life history pattern, resource requirement, and ecological

function. Effects of environmental and habitat variables in the basin assessment area on these three

types are summarized. Key ecological functions of earthworms are presented in relation to the ecological types and habitats of earthworms in the basin assessment area. These key ecological functions include the effects of earthworms on soils, their role in nutrient cycling, and their relation to

other fauna.

Distributions of earthworm species in the basin assessment area also are summarized. Although most

of the known species from the area are exotics from Europe, at least three species are native to the

region. Unpublished records indicate that there may be many more species that have either not yet

been collected or for which descriptions have not yet been published. Both the possibility of discovering additional macrofaunal biodiversity and the precarious status of at least one known species

argue for additional research on earthworms in the basin assessment area.

Effects of land use and management practices on earthworms are explored by examining research on

similar human influences in other ecosystems as no research on these issues has been done in the

Western United States. Suggestions for land use and future research priorities are provided.

Keywords: Earthworm, Oligochaeta, Columbia River basin, soil biota, land management.
Contents

1 Introduction

1 General Earthworm Ecology

3 Native and Exotic Earthworms of the Basin Assessment Area

8 Management Issues

10 Research and Monitoring Priorities 

11 Conclusion

12 References
Introduction

Earthworms (Annelida: Oligochaeta) are an

important but much neglected component of

ecosystems. It has been said that we know more

about the 2 kilograms of bird tissue flying over

each hectare than about the 200 kilograms of

earthworms working the soil of each hectare

(Bouche 1977; numbers apply to temperate

Western Europe). Understanding the key role of

earthworms in many biogeochemical cycles and

in soil development requires an understanding

of the impacts of land uses and other humancaused influences on earthworms. This is particularly true in relation to restoration of damaged

systems and to preventive maintenance to avoid

damage.

Along with the effects of earthworms on soil

development, decomposition, and nutrient

dynamics are other important considerations:

earthworms are eaten by small mammals and

birds; invasion of soil in the basin assessment

area by exotic earthworm species has occurred

in many locations and is probably ongoing;

invasions occurring in locations previously free

of earthworms likely will alter nutrient cycling

patterns, soil food webs, and potentially the

diets of small vertebrates; reduction in ranges of

native species is due to destruction of habitat,

displacement by exotic species, or by a combination of the two; and currently, not enough is

known about the native species to determine

whether they are threatened or endangered. 

The intent of this report is to supply sufficient

information about earthworm ecology in the

eastern portion of the interior Columbia River

basin (hereafter referred to as the basin assessment area) to those who make management

decisions and determine research priorities.

This paper provides a brief review of earthworm ecology, highlights their key ecological

functions, and presents distributional and ecological data for both native and exotic earthworms in the basin assessment area. Management implications and directions for future

research also are discussed.

General Earthworm Ecolog y

Earthworms are segmented worms of the phylum Annelida, class Oligochaeta. About 4,300

species are known, and many more may await

description, including some in the basin

assessment area. They differ in certain fundamental characteristics of body plan and reproductive organ layout from their close relatives

in the aquatic Oligochaeta. One basic requirement of earthworms, closely tied to their aquatic

ancestry, is moist soil in order to remain active,

because gas exchange is conducted through a

water film on the integument (Edwards and

Bohlen 1996), and burrowing is easier in moist

soil. Earthworms influence the soil environment, and that influence differs with the ecological niches of different species. More detail follows about environmental influences and constraints on earthworm populations, the effects of

earthworm activity on their ecosystems, and the

ecological differences among earthworms. 

Environmental influences on earthworms—

Three environmental factors, moisture, temperature, and pH, plus food resource quantity and

quality, are the most important influences on

earthworm populations. Soil moisture affects

earthworm abundance, activity patterns, and

geographic distribution. Soil temperature influences seasonal activity, limiting earthworms

during warm and cold periods. Soil pH often is

cited as a limiting factor on earthworm distributions, as the best studied group, European

Lumbricidae, generally does not inhabit soils

with pH below 4.0. Quality and quantity of food

resource also influence earthworm abundance.

Soil climate determines the periods of earthworm

activity. Within a habitat type, variations in soil

climatic factors occur (because of slope, aspect,

soil particle size distribution, and drainage characteristics), that result in variation in earthworm

activity period and earthworm abundance. A

forested habitat probably has a relatively buffered

soil climate compared to the more exposed

grasslands and agricultural land. Grassland temperature and moisture regimes are probably

more extreme and could accentuate the effects

1
of slope, soil properties, and other site characteristics. An agricultural cycle having long periods of bare ground could further intensify the

impact of weather on earthworms.

Although the well-known Lumbricidae typically

do not inhabit soils with pH below about 4.0,

other taxa tolerate lower pH values, including

some Pacific coast native species (pH 3.1 to

5.0; McKey-Fender and others 1994), thereby

indicating that soil acidity might be less limiting for certain earthworm species than for others.

Organic matter enters soil food webs from litter

fall or from root deposition. Surface litter may

be fed on directly or after prior ingestion and

defecation by other detritivores. Dependence on

these sources of organic matter, which are discussed later, differs by species. Quality of

organic matter differs greatly among plant

sources and can affect earthworm populations.

Organic matter may render the soil strongly

acid, could be rich in digestibility-reducing compounds, or could have a high carbon-to-nitrogen

ratio. These qualities tend to reduce earthworm

populations.

Lack of organic matter is generally a significant

limiting factor for earthworms. The fact that

most agricultural soils are depleted of organic

matter likely accounts for lower abundance of

earthworms in agricultural land or recently

abandoned cropland. 

Effects of earthworms on soils and organic

matter—Much is known about the effects of

earthworms on soil characteristics and nutrient

availability (see Edwards and Bohlen 1996, Lee

1985). Soil structure is altered by the creation

of macropores and macroaggregates. Soil profiles may be mixed vertically. Forest floor litter

layers can be entirely consumed by earthworms.

These structural alterations affect the environments and resource bases of other soil fauna,

alter the relative abundances of bacteria and

fungi in favor of bacteria, and change the patterns of water and gas movement into and within soils. Nutrient mineralization is enhanced

by earthworm activity, either by digestion,

assimilation, excretion, and tissue breakdown,

or indirectly through accelerated bacterial

attack on organic matter. All earthworm excreta

have higher levels of available macronutrients

and cations than the material ingested (see Lee

1985). Urine is a source of available nitrogen.

Also body tissues readily decompose after

death. In addition to mineralization, chemical

effects resulting from passage of soil organic

matter through earthworms increase availability of some soil mineral nutrients. Because of

the impact and generality of these phenomena,

earthworms often are considered “keystone”

members of soil and litter decomposer communities. To understand the effects of earthworms

on their environments, three ecological types

of earthworms and how they affect soils differently must be considered.

Ecological diversity among earthworms:

definitions and functional roles—Three main

ecological categories of earthworm are widely

recognized: epigeic, anecic, and endogeic

(Bouche 1977). Epigeic worms are typically

small, darkly pigmented, and reside in leaf litter

layers under the bark of decaying logs or in

other concentrations of organic material. They

have high rates of reproduction and short lifespans. Anecics inhabit a permanent or semipermanent deep vertical burrow and emerge at

night to consume relatively fresh plant detritus

on the surface. These are the largest and longest

lived earthworms. Endogeics live in the mineral

soil and consume organic matter within the soil

or at the soil-litter interface. They are larger,

less pigmented to unpigmented, have longer

lifespans, and have lower reproductive rates

than epigeic worms. All three types also consume mineral soil to varying degrees, with the

endogeics being the greatest processors of mineral soil. 

Lavelle (1983) further divided the endogeic category into polyhumic, mesohumic, and oligohumic types. Polyhumic endogeics work on richer

sources of organic matter in the early stages of

decomposition closer to the soil surface or at

the soil-litter interface. Lumbricus rubellus and

possibly Aporrectodea trapezoides are examples

of this type of earthworm, which is characterized

by moderate dorsal pigmentation and modest

development of intestinal surface area. Intestinal

2
structures that increase gut surface area are

most highly developed in the oligohumic endogeics found deeper in the soil and feeding on

more decomposed organic matter. Intestinal surface area is least developed in epigeics and

anecics. Mesohumic endogeics have little or no

pigmentation, intermediate secondary development of intestinal surface area, and poorly

developed escape behavior. Feeding is on welldecomposed organic matter.

The diverse life patterns of the different ecological types of earthworms cause different functional roles or effects on the ecosystem of each

species. The preceding general overview of the

effects of earthworms on soils and soil processes

should be understood in the contexts of the different ecological types of earthworms. The next

level of refinement of understanding would be

species-specific knowledge of functional roles

of earthworms; this information, however, is not

known for any of the native species in the basin

assessment area, thus ecological type is the

extent of our discussion. 

Epigeic earthworms, which are generally forest

dwellers, likely serve the following functions: 

• Organic matter comminution—Reducing the

size of organic matter particles during passage

through the worm makes organic matter more

accessible to digestive action by other decomposers. 

• Nutrient cycling—Earthworms digest organics

and thus mineralize some of the nutrients

bound in them. 

• Soil structure modification—Burrowing and

defecating create soil structures significant

(though the details are unknown) to other soil

biota. The soil structures created are hydrologically significant, and soil water-stable aggregation is promoted. 

• Transfer of organic matter to the soil—Consumption of surface litter results in defecation

in the mineral soil, particularly if worms retreat

into the mineral soil to avoid unfavorable climatic conditions in the litter.

• Food for other animals—Predators of earthworms include small mammals, feral pigs,

beetle larvae, centipedes, some flies, and birds. 

Anecic earthworms transfer relatively fresh plant

litter from the surface to deep levels of the soil,

thereby creating deep vertical burrows, which

enhance water infiltration. Other earthworm types

can contribute to these processes but generally

do not. Anecics also provide food resources to

endogeic worms by depositing fecal organic

matter (or casts) into the soil where endogeics

can reach it. 

Functional roles of endogeic earthworm are

similar to those mentioned for the epigeic

species, with the following modifications: 

• Soil profile development or transfer of materials within the soil—Defecation within the mineral soil will not always be at the same level as

consumption. Deposition of casts may occur

on the soil surface, in which case mineral soil

is being brought up to the surface, and upper

soil horizon material may be being deposited

in the deeper strata. 

• Soil carbon protection—Endogeic earthworms

produce fecal pellets, which are water-stable

aggregates, and within which soil carbon is

partially protected from oxidation. Although

the initial evolution of a cast includes a phase

in which microbial respiration of soil carbon is

enhanced, the long-term effect of the incorporation of organic matter into casts is to slow

the oxidation of soil carbon (Lavelle and Martin

1992). In this way, earthworms contribute to

the soil carbon sink. 

With some basic knowledge of earthworm ecology, we can now consider the status of earthworms in ecosystems of the basin assessment

area, specifically their distribution and ecology.

We also will discuss management priorities.

Native and Exotic Earthworms of

the Basin Assessment Area

The state of present knowledge—Presently,

little is known about earthworms in the basin

assessment area. Although much of the region is

3
4

Figure 1—Collection pointsfor native and exotic earthworms in the Columbia River basin. Two sources for some of the collection point information are Fender (1985) and Gates (1967). 

Legend

Exotic Earthworms

Aporrectodae

trapezoides

Eiseniella tetraedra

Dendrobaena rubidaLumbricus rubellusOctolasion tytraeumLumbricus terrestrisAllolobophora

tuberculata

Apporrectodea roseaBimastos parvusApporrectodea turgida

Allolobophora

chlorotica

Native Earthworms

Drilochaera

chenowithensis

Argilophilus hammondiDriloleirus americanusState boundariesColumbia River basin

assessment boundary
too arid to support earthworms, many habitats

do have earthworms, both native and exotic.

Lack of knowledge of native earthworm fauna,

some of which may be endangered by habitat

loss, is a cause for concern. Undescribed

species are likely present in the region. Nothing

is known of how native species contribute to

ecosystem processes in the basin assessment

area, or of how they interact with other species,

such as earthworm predators. On the other

hand, many exotic species occur in the basin

assessment area, possibly altering previously

worm-free soils and nutrient cycling pathways,

competing with native species, and generally

modifying any processes linked to soil physical or chemical properties. 

The known distributions of earthworms in the

basin assessment area are shown in figure 1

(Fender 1985, Gates 1967). Many of the distribution marks are tightly clustered because several species were found at one site; hence a

cluster is generally one site, not several neighboring ones. Published data on earthworms of

the basin assessment area thus are based on a

limited number of collection locations. Only a

small portion of the earthworm-inhabitable

basin assessment area has been surveyed.

Fender1 indicates that five native genera are represented in the basin assessment area: Driloleirus,

Drilochaera, Argilophilus, Arctiostrotus, and

Macnabodrilus; however, only three species

have been described. Driloleirus americanus

is known from eastern Washington and western Idaho. Driloleirus americanus may be

anecic, based on its deep burrowing habits and

largely organic diet. Drilochaera chenowithensis is known from only one site along the

Columbia River at Chenowith Creek, west of

The Dalles, Oregon (McKey-Fender 1970).

Argilophilus hammondi has been found at the

Chenowith Creek site and well to the south in

the Ochoco National Forest on the slopes of 

Grant Butte in Crook County, in an open ponderosa pine (Pinus ponderosa Dougl. ex Laws.)

forest with sedges and grasses in the understory,

and at an elevation of about 1600 meters

(McKey-Fender 1970). These native genera

have other species on the west side of the

Cascade Range. Argilophilus ranges well to

the south into California to the latitude of

Riverside, California (Wood and James 1993).

The factors that influence native species populations are unknown. Only by assuming that

they are comparable to those of other earthworms can it be said that soil moisture, soil

temperature, organic matter quantity and quality, and soil pH are probably the most important

factors (Lee 1985). We have, however, already

narrowed the consideration to specific habitat

types; and those probably fall within the limits

of tolerance of most temperate zone endogeic

earthworms.

Because much research has been done on the

ecology of European earthworm species, more

is known about the exotics than about the native

species of the basin assessment area. The

European species Dendrobaena rubida and the

eastern North American Bimastos parvus are

epigeic. Eiseniella tetraedra (also native to

Europe) has epigeic physical and life history

characteristics, but it is semiaquatic. Bimastos

parvus was found in Engelmann spruce-subalpine fir (Picea engelmannii Parry ex Engelm.-

Abies lasiocarpus Hook. Nutt.) cover under logs

and stones, whereas Dendrobaena rubida was

found in a riparian area within agricultural land

(Gates 1967).

Lumbricus terrestris (common name: nightcrawler) is a European anecic species. It was

recorded from two artificial environments, a lawn

at the University of Idaho and in a roadside picnic area near Pocatello, Idaho (Gates 1967). 

The native species Drilochaera chenowithensis

and Argilophilus hammondi are probably endogeic, based on the physical characteristics given

in McKey-Fender (1970). European endogeic

species recorded thus far are Aporrectodea

trapezoides, A. tuberculata, Eisenia rosea, 

5

1 Personal communication. 1996. Fender, W.M. Soil Biology

Associates, 835 Ashwood Avenue, McMinnville, OR 97128-6801.
Lumbricus rubellus, and Octolasion tyrtaeum.

All these species are widely distributed in North

America because of human activity.

Habitat factors important to earthwormsin

the basin assessment area—Both the potential

roles of earthworms in basin assessment area

ecosystems and the possible impact of management decisions on earthworms can be roughly

predicted by considering the habitat requirements

of the main ecological types of earthworms in

relation to the climates and vegetation cover

types of the basin assessment area. In addition

to simple edaphic parameters and soil properties, the age and species composition of specific

vegetation types are important.

Soil pH level often is cited as a limiting factor

to the establishment of earthworms in boreal

forests or other acid soils. If any of the higher

elevation forests have this characteristic, earthworms may be restricted from those sites. The

species present in the basin assessment area are

mostly exotics with proven abilities to handle

wide variations in soil conditions, such as

Aporrectodea trapezoides. The known native

species tolerant of acid soil are from the west

slope of the Cascade Range. Within the basin

assessment area, Argilophilus hammondi was

collected from two ponderosa pine sites of pH

5.5 and 6.0, values tolerable to almost any

earthworm.

Epigeic earthworms require plant remains in

early stages of decomposition and typically live

in accumulations of organic material such as

forest litter layers. Some species such as

Dendrobaena rubida and Bimastos parvus are

frequently found in down woody material. To

harbor epigeic species, a forest stand must

either grow under conditions that permit development of a litter layer or be old enough to

produce down woody debris, or both. Leaf litter

depth must be sufficient to provide moisture

retention in the lower layers of the litter between

rains so the worms can feed on the litter. Three

to six centimeters of litter and humified organic

matter is a safe minimum. Because these worms

are so active, they can find deep litter accumulations and woody debris, provided the moisture

regime is favorable. 

Down wood of 10 centimeters diameter will

have sufficient bark and decomposing cambial

layers to support these worms. The stage of

decay and species of tree, however, are important.

Logs in contact with the ground and reaching

the state at which the bark is loose but not yet

falling off are most likely to harbor these worms.

In eastern forests, log-dwelling species seem

less likely to be encountered in down oak and

conifer logs, and more often are found in

species such as maple, birch, aspen, tulip

poplar (Liriodendron tulipfera L.), and cherry.

It is unknown whether any native epigeic

species are in the basin assessment area and, if

so, whether any of them utilize logs.

Anecic species can live in forested or grasslandshrubland areas provided they can escape deep

into the soil when soil climate is outside their

activity range. The only other known requirement is sufficient quality and quantity of litter

production to sustain earthworm growth and

reproduction. Because this factor is strongly

controlled by water availability, litter quality is

more likely to be an issue than litter quantity.

Endogeic species seem to have the broadest

habitat ranges. In the basin assessment area,

endogeic species occurred in a wide range of

habitats, including forests, savannah, grasslandshrubland (including exotic grass pasture and

seral stages following cessation of agriculture),

and cultivated land. The primary factors accounting for the distribution of exotic species in the

basin assessment area are a combination of

accidental introduction by humans and the

availability of sufficient moisture where these

accidental introductions have occurred. In the

basin assessment area, native endogeics are

probably confined to higher elevations and

riparian areas. They may be absent from some

inhabitable areas because of historical geological and climatic conditions of different regions

within the basin assessment area. 

6
Biogeography—The eastern portion of the basin

assessment area contains diverse land forms,

soils, and vegetation types, some of which harbor earthworms. Distributions of native and

exotic earthworms in the basin assessment area

depend on many historical factors in addition to

the general soil climatic requirements of earthworms. Large-scale climate changes, vulcanism, and substrate evolution could affect the

presence or absence of native species in

regions where current conditions are favorable.

Human activity has had a tremendous impact,

both by destroying habitat and by inadvertently

introducing exotic species.

Presently, there is insufficient published information to allow us to identify areas of high

diversity or endemism or to outline regions

where past climate or geological influences are

responsible for earthworm absence from habitable conditions. On the local scale, earthworms

in temperate zones generally show low withinsite diversity, with three to six species per site.

In topologically complex land areas, many

species have limited distributions, which leads

to high diversity among sites. For example, New

Zealand has about 200 species of earthworms,

but seldom are more than four found in any one

spot (Lee 1959). Fender (see footnote 1) estimates

the Pacific coast earthworm fauna to contain 80

to 100 species, including many undescribed

basin assessment area species. Given the size

and topographic diversity of the basin assessment area, a conservative estimate of the eventual number of earthworm species there might

be about 20. 

Forest Service and Bureau of Land Management

lands, particularly the former, are likely to harbor most surviving native earthworm species

populations in the basin assessment area. Interior

ponderosa pine and Douglas-fir (Pseudotsuga

menziesii Mirb. Franco) forests and other nonxeric habitats probably support the native

species. Forest Service and Bureau of Land

Management lands near fishable streams or

human settlements also may harbor exotic

species. The Steens Range, bitterbrush areas,

juniper stands, and sagebrush are thought to

lack earthworms (see footnote 1). Fender suggests that native species tend to favor fine-textured soils, whereas European Lumbricidae

species can more easily invade coarse-textured

soils. This could possibly be related to the

prevalence of human activity along watercourses

with their alluvial coarse soils.

Among land areas outside of Forest Service and

Bureau of Land Management land areas, riparian zones, privately owned grazing land, and

timber land are most likely to contain native and

exotic earthworms; agricultural land, particularly

dryland farms, is less likely to contain either.

Earthworms have been recorded from sites

within cover types shown in basin assessment

area current vegetation cover type maps (Eyre

1980, Hann and others 1997, Shiflet 1994),2

and where available, collection data from Gates

(1967) and McKey-Fender (1970): SAF 206

(Englemann Spruce-Subalpine Fir), SAF 210

(Interior Douglas-Fir), SAF 213 (Grand Fir),

SAF 218 (Lodgepole Pine), SAF 237 (Interior

Ponderosa Pine); SRM 107 (Western Juniper,

Big Sagebrush, Bluebunch Wheatgrass), SRM

109 (Ponderosa Pine-Shrubland), SRM 110

(Ponderosa Pine-Grassland), SRM 304 (Idaho

Fescue-Bluebunch Wheatgrass), SRM 607

(Wheatgrass-Needlegrass); CRB 001

(Agricultural land), CRB 002 (Mixed grassagriculture-shrubland), and CRB 004 (Subalpine herbaceous). The following additional

vegetation cover types from Gates (1967) and

McKey-Fender (1970) likely could be inhabited

by earthworms: CRB 003 (Seral shrublandregeneration), SAF 217 (Aspen), SAF 235

(Cottonwood-Willow), SRM 103 (Green Fescue),

SRM 306 (Idaho Fescue-Slender Wheatgrass),

and SRM 402 (Mountain Big Sagebrush).

Sensitivity to disturbance and population trends

are unknown for all the native species. Collection

data from Fender (see footnote 1) and McKey7

2 Columbia River basin succession model, (CRBSUM) current

vegetation cover types map. 1996. On file with: USDA Forest

Service; USDI Bureau of Land Management, Interior Columbia

Basin Ecosystem Management Project, 112 East Poplar Street,

Walla Walla, WA 99362. Also available on line: www.basinemp.

gov/spatial/.
Fender (1970, 1994), however, suggest that virtually any disturbance that alters vegetation or

allows the entry of exotic species can possibly

reduce or eliminate native species populations.

Because their observations are not based on

experimental manipulations, it would be difficult to define what conditions would threaten or

endanger native species. We also do not know

the degree to which habitat disturbance and

ecological competition contribute to the

replacement process. More information on this

issue is presented in the next section.

The exotic species from Europe have achieved

their current global temperate zone distribution

because of their broad adaptability to different

habitats and their resilience following disturbance. Populations likely are expanding in numbers and geographic extent as movements of

individual species (basically a diffusion process)

and accidental transport by humans enlarge the

occupied territory.

Management Issues

Biodiversity concerns: preservation of native

species and alterations to the ecosystem

caused by exotics—The basin assessment area

is inhabited by at least three native earthworm

species belonging to three genera. All three

should be of special concern. The giant earthworm, Driloleirus americanus, was considered

for inclusion in Wells and others (1983) because

its habitat was threatened and its range was

small. Current information suggests that it may

be a narrow endemic using a threatened habitat

(shrubland sites with good soil). The collection

data give little detailed information about habitat type. The three sites (near Pullman and

Ellensberg, Washington, and Moscow, Idaho

[Fender and McKey-Fender 1990]) are located

in what is now agricultural land, grassland, and

shrubland (CRB 001, 002).

The other two native species, Drilochaera

chenowithensis and Argilophilus hammondi,

may be somewhat tolerant of habitat disturbance. Their type localities were on uncultivated

canyon and surrounded by orchards (McKeyFender 1970). They therefore may be considered

more likely to survive but probably still should

be given special attention. In particular, learning

more about their ranges and ecological flexibility would enable land managers to determine

whether or not special measures are necessary.

This leads to another area of concern to land

managers: invasion by exotic species. Exotic

earthworm species present in the basin assessment area are (thus far) all of European origin

and are all members of the family Lumbricidae,

with the exception of one species indigenous to

America (Bimastos parvus). This invasion is a

cause for concern for two reasons. First, these

species may be able to outcompete native

species. Replacement of native species by

exotics has been observed in many parts of the

world, including northern California (Eisen

1900), Illinois (Smith 1928), New Zealand (Lee

1961), and South Africa (Ljungstrom 1972). In

general, native earthworms are vulnerable to

habitat disturbance and invasion by exotic

species (Kalisz and Dotson 1989). Large areas

of intact habitat seem to be somewhat more

resistant to native species loss, though the longterm outcome is not known.

The second reason for concern arises in regions

where native earthworms do not occur. This

absence may be for many reasons, such as

glaciation, long dry periods, and isolation from

potential colonists by intervening deserts. Soil

and litter development in the absence of worms

is different from that in soil inhabited by

worms, particularly in forest ecosystems (for

example, Langmaid 1964). There may be corresponding differences in the nutrient cycling

dynamics, soil mesofauna, soil microfauna, and

soil microflora of worm-free and worm-inhabited

systems.

Sich concerns have led to the following questions: Do land managers wish to maintain wormfree areas in their natural state? Is it important

to maintain native species, or for larger purposes of sustainable land use, is any worm good

enough? Efforts to control the spread of exotic 

8
earthworms may be futile, and insufficient information exists about the relative ecological

impact of native and exotic species to allow

decisionmakers to make informed decisions

about how to manage earthworm biodiversity.

Land uses, earthworms, and earthworm

functions—The fundamental issue here is

whether or not the ecological functions of and

biodiversity concerns about earthworms are sufficiently important to shape management decisions. In some soil systems within the basin

assessment area, earthworms function as keystone organisims; as such, they merit inclusion

with other more conspicuous organisms. We

now know that earthworm introductions alter

previously worm-free soils and can potentially

cause various effects on other groups of soil

biota and on nutrient cycling processes. Vital

data are lacking about biodiversity and about

whether certain species may be endangered,

either from habitat alteration or from the introduction of exotics. We do not have experimental

evidence directed specifically at those basic

management questions for which earthworm

data could be relevant. For now, and as a stimulus for further inquiry, I have assembled some

basic information on the impacts of grazing,

prescribed fire, and logging on earthworms.

These three land uses or management practices

are widespread and economically important to

the region.

Grazing—Effects of grazing on earthworms

include at least three components. First, manure

deposition on the soil surface reduces available

leaf litterfall. Second, root death results from

grazing, and thus rhizodeposition of detritus in

the soil is increased (up to a point). Third, livestock can cause soil compaction, thereby making burrowing and feeding more difficult for

earthworms.

Conversion of herbage to manure by cattle

changes the quality and accessibility of detrital

material for earthworms. What would have been

litter is now partly predigested, may be toxic in

the short term, is clumped rather than dispersed,

and is highly attractive to several other invertebrates. James (1992) describes the response of

several earthworm species to bison (Bison

bison) dung pats in tallgrass prairie. Species

with characteristics of polyhumic endogeics

(including Aporrectodea turgida—present in

the basin assessment area) were attracted to

dung, whereas other endogeics were not. Other

categories of worms were not represented in the

system.

Hutchinson and King (1980) examine the effects

of sheep stocking rates on soil invertebrate populations, and Seastedt (1985) and Seastedt and

others (1986) consider the impact of clipping or

mowing on soil arthropods. In general, these

studies showed a peak of abundance at moderate

plant defoliation levels. The results, however,

are not as clear with earthworms: Seastedt and

others (1988) are inconclusive, but Todd and

others (1992) found increased abundance of

some species with increased mowing frequency

but no change (statistically insignificant declines

of biomass) for other species. Consequently, it

seems that any assessment of the impact of various grazing management scenarios will have to

be case by case.

Soil compaction caused by animal activity

(including humans) has variable effects on

earthworm populations. Cuendet (1992) found

contrasting effects of pedestrians on earthworms

in two forest types; whereas Pizl (1992) found

that the farm machinery in orchards negatively

affects all earthworms. Different ecological categories of worms were affected to differing

degrees in each case. More specifically, cattle

trampling has a blanket negative effect that

results in a decline in earthworm population

but is less intense on large-bodied earthworms

(Cluzeau and others 1992). In this study, trampling was intense, such as would be found by

gateways or at water sources. 

All three effects of grazing considered here

show variable effects by earthworm species or

habitat type or both. Endogeic species often suffered less than epigeics, and large species were

also less heavily impacted. Without further

knowledge about native earthworms and the

presence or absence of earthworms in land subject to grazing in the basin assessment area, it is

of little use to speculate further.

9
Prescribed fire— James (1988) describes the

impact of fire in Kansas tallgrass prairie on

native earthworm populations. The effect was

positive because fire allows more rapid warming of the soil in spring, thereby stimulating

growth of grasses. In contrast, European species

declined with burning, probably because they

were less able to tolerate the higher soil temperatures on burned plots. Fire, as a management

tool, thus may be short-term neutral or positive

on native endogeic species where fire is a natural

and frequently recurring element of the ecosystem. If invasions by exotic species occur near

their temperature tolerance limits under firesuppression conditions, they may be pushed

beyond the limits in the postfire environment.

Anything that removes a litter layer and down

logs could negatively impact epigeics. Additional

information more relevant to forest fires can be

found in Abbot (1984, 1985), though the work

was done in jarrah forests of Australia.

Logging—The primary effects of tree removal

on endogeic species seem to be in the soil climate area, with surface and soil organic matter

pools probably sufficient to carry them through

until second-growth plants become established.

If selective cutting practices are adopted, this

impact will be moderated. Dis-turbance caused

from heavy equipment use may be the most

deleterious (Schaefer and others 1990).

Epigeic species would be expected to suffer

most from the loss of tree cover because this

would make their preferred microhabitat less

hospitable and ultimately less abundant, with

the loss of annual leaf input. There may be a

short-term increase from slash left on site, but it

is difficult to say if the microclimate would

remain suitable for earthworm activity.

The previously mentioned land uses and the

management practices linked to them will

affect earthworms. Considering that basin

assessment area habitats likely to be inhabited

by earthworms are generally those with enough

precipitation to support some sort of economically driven land use, practical human activity,

management decisions, and the fates of earthworm populations could be strongly related in

the basin assessment area. Federal and private

land decisionmakers in this diverse region may

choose to incorporate earthworm ecology and

biodiversity parameters in the information used

in making management decisions.

Research and Monitoring Priorities

Complete rectification of the lack of information

about earthworms in the basin assessment area

is probably beyond the budgetary and scientific

infrastructure resources (particularly the supply

of experts) available. The most critical research

need is an inventory of the species present, particularly the native species, and their geographical

distribution. An inventory will simultaneously

tell us much about the distribution of exotic

species in the basin assessment area. The unprocessed collection information of Fender

(see footnote 1) and McKey-Fender (1990)

could be worked up, and survey efforts could be

made to extend their work. Another high priority would be experimentally testing hypotheses of

the mechanisms through which habitat disturbance, exotic species invasions, and other

human-caused factors may affect native species.

This should begin with those species potentially threatened both in the basin assessment area

and globally, such as Driloleirus americanus.

The next priorities would be to learn more

about the population densities, habitat requirements, and general ecology of native species in

the basin assessment area. An equally important priority for the exotic species would be

research into their effects on litter decomposition, soil horizon development, and other soil

invertebrates in regions otherwise free of earthworms. 

Once the high-priority areas of research are covered, a basis for deciding the next direction for

earthworm research in the basin assessment area

could be determined. Native species existing as

dense populations in particular vegetation types

have a higher priority for process- and community-level investigation than species naturally

occurring in low numbers. Integrated research

with specialists on other basin assessment area

biota is highly desired. Interactions with fungi,

or earthworms as food resources for vertebrates,

10
are some examples where high-priority organisms in forest ecology and wildlife conservation

would be involved. Because little is known

about the earthworms of the basin assessment

area, research could begin on almost any one of

the priorities. 

Conclusion

Earthworms, called “the intestines of the earth”

by Aristotle, are important to soil processes,

other soil biota, and soil hydrology. Although

large areas of the basin assessment area are too

dry to support earthworms, they have been

recorded in various habitats. Both exotic and

native earthworm species exist in the basin

assessment area. This report presents the basic

ecological information necessary to begin evaluating the effects of land management practices

and conservation policy on earthworm populations. In addition, the question of how to

respond to the presence of invasive exotics has

been raised. Findings presented in this paper

provide a starting point, a source of hypotheses

to be examined in future research efforts and

discussions on ways to preserve our natural

landscapes and their inhabitants. 

11
References

Abbot, I. 1984. Changes in the abundance and activity of certain soil and litter fauna in the jarrah

forest of western Australia after a moderate intensity fire. Australian Journal of Soil Research. 22:

463-469.

Abbot, I. 1985. Influence of some environmental factors on indigenous earthworms in the northern

jarrah forests of western Australia. Australian Journal of Soil Research. 23: 271-290.

Bouche, M.B. 1977. Strategies lombriciennes. In: Soil organisms as components of ecosystems.

Ecological Bulletin (Stockholm). 25: 122-132.

Cluzeau, D.; Binet, F.; Vertes, F. [and others]. 1992. Effects of intensive cattle trampling on soilplant-earthworms system in two grassland types. Soil Biology and Biochemistry. 24: 1661-1665.

Cuendet, G. 1992. Effect of pedestrian activity on earthworm populations of two forests in

Switzerland. Soil Biology and Biochemistry. 24: 1467-1470.

Edwards, C.A.; Bohlen, P.J. 1996. Biology and ecology of earthworms. 3d ed. London, England:

Chapman and Hall. xii + 449 p.

Eisen, G. 1900. Researches in American Oligochaeta, with especial reference to those of the Pacific

Coast and adjacent islands. In: Proceedings of the California Academy of Sciences. II(2): 85-276.

Eyre, F.H., ed. 1980. Forest cover types of the United States and Canada. Washington, DC: Society

of American Foresters. 148 p. [Plus map].

Fender, W.M. 1985. Earthworms of the western United States. Part I. Lumbricidae. Megadrilogica.

4: 93-132.

Fender, W.M.; McKey-Fender, D. 1990. Oligochaeta: Megascolecidae and other earthworms from

western North America. In: Dindal, D.L., ed. Soil biology guide. New York: Wiley and Sons.

Gates, G.E. 1967. On the earthworm fauna of the great American desert and adjacent areas. Great

Basin Naturalist. 27: 142-176.

Hann, Wendel J.; Jones, Jeffrey L.; Karl, Michael G. [and others]. 1997. Landscape dynamics of

the basin. In: Quigley, Thomas M.; Arbelbide, Sylvia J., tech. eds. 1997. An assessment of ecosystem components in the interior Columbia basin and portions of the Klamath and Great Basins.

Gen. Tech. Rep. PNW-GTR-405. Portland, OR: U.S. Department of Agriculture, Forest Service,

Pacific Northwest Research Station. Vol. 2. Chapter 3. (Quigley, Thomas M., tech. ed.; Interior

Columbia Basin Ecosystem Management Project: scientific assessment).

Hutchinson, K.J.; King, K.L. 1980. The effects of sheep stocking level on invertebrate abundance,

biomass and energy utilization in a temperate sown grassland. Journal of Applied Ecology. 17:

368-387.

James, S.W. 1988. The postfire environment and earthworm populations in tallgrass prairie.

Ecology. 69: 476-483.

James, S.W. 1992. Localized dynamics of earthworm populations in relation to bison dung in North

American tallgrass prairie. Soil Biology and Biochemistry. 24: 1471-1476.

Kalisz, P.J.; Dotson, D.B. 1989. Land use history and the occurrence of exotic earthworms in the

mountains of eastern Kentucky. American Midland Naturalist. 122: 288-297.

Langmaid, K.K. 1964. Some effects of earthworm invasion in virgin podzols. Canadian Journal of

Soil Science. 44: 34-37.

12
Lavelle, P. 1983. The structure of earthworm communities. In: Satchell, J.E., ed. Earthworm ecology,

from Darwin to vermiculture. London, England: Chapman and Hall: 449-467.

Lavelle, P.; Martin, A. 1992. Small-scale and large-scale effects of endogeic earthworms on soil

organic matter dynamics in soils of the humid tropics. Soil Biology and Biochemistry. 24: 1491-

1498.

Lee, K.E. 1959. The earthworm fauna of New Zealand. New Zealand Department of Scientific and

Industrial Research Bulletin 130. 486 p.

Lee, K.E. 1961. Interactions between native and introduced earthworms. Proceedings of the New

Zealand Ecological Society. 8: 60-62.

Lee, K.E. 1985. Earthworms—their ecology and relationships with soils and land use. [Place of publication unknown]: Academic Press. 411 p.

Ljungstrom, P.O. 1972. Taxonomical and ecological notes on the earthworm genus Udeina and a

requiem for the South African acanthodriles. Pedobiologia. 12: 100-110.

McKey-Fender, D. 1970. Description of endemic earthworms from eastern Oregon (Oligochaeta:

Acanthodrilidae). Northwest Science. 44: 235-243.

McKey-Fender, D.; Fender, W.M.; Marshall, V.G. 1994. North American earthworms native to

Vancouver Island and the Olympic Peninsula. Canadian Journal of Zoology. 72: 1325-1339.

Pizl, V. 1992. Effect of soil compaction on earthworms (Lumbricidae) in apple orchard soil. Soil

Biology and Biochemistry. 24: 1573-1576.

Schaefer, D.J.; Seastedt, T.R.; Gibson, D.J. [and others]. 1990. Field bioassessments for selecting

test systems to evaluate military training lands in tallgrass prairie. Ecosystem Health V.

Environmental Management. 14: 81-93.

Seastedt, T.R. 1985. Maximization of primary and secondary productivity by grazers. American

Naturalist. 126: 559-564.

Seastedt, T.R.; Hayes, D.C.; Petersen, N.J. 1986. Effects of vegetation, burning and mowing on

soil macroarthropods of tallgrass prairie. In: Clambey, G.K.; Pemble, R.H., eds. Proceedings of the

9th North American prairie conference; [Dates of proceedings unknown]; Moorhead, MN. Fargo,

ND: Tri-College Press: 99-102.

Seastedt, T.R.; James, S.W.; Todd, T.C. 1988. Interactions among soil invertebrates, microbes and

plant growth in the tallgrass prairie. Agriculture, Ecosystems and Environment. 24: 219-228.

Shiflet, T.N., ed. 1994. Rangeland cover types of the United States. Denver, CO: Society of Range

Management. 152 p.

Smith, F. 1928. An account of changes in the earthworm fauna of Illinois and a description of one

new species. Illinois Natural History Survey Bulletin. 17: 347-362.

Todd, T.C.; James, S.W.; Seastedt, T.R. 1992. Soil invertebrate and plant responses to mowing and

carbofuran application in a North American tallgrass prairie. Plant and Soil. 144: 117-124.

Wells, S.M.; Pyle, R.M.; Collins, N.M.; Hughes, S.A. 1983. The IUCN invertebrate red data book.

Gland, Switzerland: International Union for the Conservation of Nature. 632 p.

Wood, H.B.; James, S.W. 1993. Native and introduced earthworms from selected chaparral, woodland, and riparian zones in southern California. Gen. Tech. Rep. PSW-GTR-142. Albany, CA: U.S.

Department of Agriculture, Forest Service, Pacific Southwest Research Station. 20 p. 

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