Arthropods and Annelid Worms

Narrative on arthropods and annelid worms of old-growth and late successional conifer forests, mature riparian woods, and of coarse woody debris associated arthropods within the range of the northern spotted owl (Strix occidentalis caurina)


The Phylum Arthropoda includes species broadly known as joint-legged animals, include crustaceans (shrimp, crayfish, isopods, etc.), millipedes, centipedes, arachnids (spiders, mites, harvestmen, etc.), and insects. The Phylum Annelida includes the earthworms of which only two species are included here.

The number of Arthropoda species that are native to the range of the northern spotted owl has not been accurately estimated, but a very rough range would be about 50,700-70,000.

More than 3,500 insect species have been sampled and identified from the Andrews Experimental Forest in Linn and Lane counties, Oregon, but the number of insect species found there alone is probably twice that number. Considering the region as a whole, only about a quarter of the insects are found at the Andrews Experimental Forest so that there are probably at least 30,000 insects species native to the range of the northern spotted owl. Some scientists have estimated that there may be as many mite species as insects, although only a small fraction have been described scientifically, but there are many fewer species of millipedes, centipedes, and crustaceans.

There are arthropods at all trophic levels except producer and in all habitats found within the range of the northern spotted owl. The tremendous variety of species and the lack of published knowledge about most has meant that only a few species could be considered in this document. Many species have not yet been described scientifically, and ecological and life history information is often not known about those that have been described. Furthermore, available locality data are usually sparse and are not available on electronic media. Most recorded collections are from public lands and private lands are essentially unsurveyed.

Criteria for Sensitive Species

The Annelida and Arthropoda included in this chapter were selected as sensitive species on the basis of several criteria. First, species listed as Endangered or Threatened under the Endangered Species Act of 1973 were included if their range was within that of the northern spotted owl and if any change in forest management within that range would conceivably have an effect on their habitat (USDI, 1988a, 1988b. Secondly, species listed as candidates in the Fish and Wildlife Service's notice of review on animal species (USDI, 1991) were included if they occur within the range of the northern spotted owl in habitats that might be negatively affected by changes in forest management practices. Finally, species not presently on any Federal or state lists were included if it was felt that they might be significantly affected in a negative way by changes in forest management practices due to any of the alternatives being considered by this impact statement. The Fish and Wildlife Service has carried out only cursory assessments of the Annelida and Arthropoda within the range of the northern spotted owl (FEMAT, 1993), while the states within the range of the owl have not carried out any assessments of native arthropods or annelids within the habitats occupied by the northern spotted owl. In some instances, species were included if there was any doubt about their sensitivity. It is entirely possible with further information that some of the species selected may not be sensitive.

All Federally listed and candidate Arthropoda (there are no Annelida) anywhere near the range of the northern spotted owl were considered on the basis of their geographic occurrence and occupied habitats as to the likelihood that they would be affected by any management actions involving the northern spotted owl. Most were not likely to be affected and not further considered in this chapter.

One species of Annelida, the Oregon earthworm (Megascolides macelfreshi Smith) was included in the IUCN Invertebrate Red Databook (Wells et al., 1983) and could conceivably be affected by the actions considered in this impact statement.

An effort was made to compile a list of Annelida and Arthropoda that might be affected by changes in management practices related to the alternatives being considered. Lists of arthropods found in previous documents and comment letters related to environmental considerations involving the northern spotted owl were carefully considered as well as were those arthropods included in any published literature on the arthropods of old-growth or mature forests within the range of the northern spotted owl. Selected arthropod specialists at institutions within the range of the northern spotted owl were canvassed for suggestions as to which arthropods species might be considered in this environmental assessment. All institutions canvassed and all persons who provided information are listed in the acknowledgments in Appendix G.

The sensitivity of species to the alternatives being considered was based on several factors. First, species whose ranges were mostly within the owl's range were considered sensitive if their preferred habitat was likely to be strongly affected or eliminated due to changes in forest management brought about by the alternatives being considered. Secondly, species whose ranges were limited to a small part of the owl's range were included as sensitive even if their habitats might not be as sensitive as those of some of the more broader ranging species.

Because the location of most populations of the insects under consideration has not been determined and negative data was not reported except in a few cases, assumptions were made about the range and habitat occurrence of each species. The northern, southern, coastal, and inland extremes in occurrence were assumed to approximate those localities reported in the literature or on determined specimens in the collections examined. It was also assumed that the species occur on private lands adjacent or nearby to sampled localities on public lands.

The species considered as sensitive are divided into several gross "functional group" categories. These categories are:

  • Canopy herbivores
  • Understory and forest gap herbivores
  • Coarse wood chewers and comminutors
  • Litter and soil dwelling species
  • Pollinators
  • Aquatic herbivores, detritivores, and predators
  • Riparian herbivores and predators
  • Forest predators
  • Forest omnivores

Although no specific species are listed, two other functional categories are important enough to be discussed:

  • Vertebrate parasites and inquilines
  • Insect parasitoids

Account Assignment:

Paul Opler
Rod Crawford
John D. Lattin - Department of Entomology, Oregon State University, Corvallis, Oregon 97331


For providing access to museum data, for suggesting taxa to be considered, or sharing information:
Dr. Richard Atkinson, Dallas, Texas
Mr. Thomas S. Briggs,California Academy of Sciences, San Francisco
Dr. John A. Chemsak, University of California, Berkeley
Mr. Rod Crawford, University of Washington, Seattle
Dr. Howell V. Daly, University of California, Berkeley
Dr. John T. Doyen, University of California, Berkeley
Dr. Rosser W. Garrison, Azusa, California
Dr. Paul Hammond, Oregon State University, Corvallis
Mr. John Hinchliff, Portland, Oregon
Dr. David H. Kavanaugh, California Academy of Sciences, San Francisco, California
Dr. Boris C. Kondratieff, Colorado State University, Fort Collins, Colorado
Dr. Jeffrey Miller, Oregon State University, Corvallis, Oregon
Dr. Robert M. Pyle, Gray's River, Washington
Dr. Norman Penny, California Academy of Sciences, San Francisco, California
Dr. Jerry A. Powell, University of California, Berkeley, California
Mr. Ron Robertson, Petaluma, California


For providing data from official files:
Ms. Diana Hwang, U.S. Fish and Wildlife Service, Portland, Oregon
Mr. Chris Nagano, U.S. Fish and Wildlife Service, Sacramento, California


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