Roadless Areas
Home/Species/ Smoky Taildropper

Prophysaon humile

Cockerell, 1890

Smoky Taildropper

G3Vulnerable Found in 1 roadless area NatureServe Explorer →
G3VulnerableGlobal Rank
HighThreat Impact
Identity
Unique IDELEMENT_GLOBAL.2.114046
Element CodeIMGAS62070
Record TypeSPECIES
ClassificationSpecies
Classification StatusStandard
Name CategoryInvertebrate Animal
Endemicendemic to a single nation
KingdomAnimalia
PhylumMollusca
ClassGastropoda
OrderStylommatophora
FamilyArionidae
GenusProphysaon
Concept Reference
Turgeon, D. D., J. F. Quinn, Jr., A. E. Bogan, E. V. Coan, F. G. Hochberg, W. G. Lyons, P. M. Mikkelsen, R. J. Neves, C. F. E. Roper, G. Rosenberg, B. Roth, A. Scheltema, F. G. Thompson, M. Vecchione, and J. D. Williams. 1998. Common and scientific names of aquatic invertebrates from the United States and Canada: Mollusks. 2nd Edition. American Fisheries Society Special Publication 26, Bethesda, Maryland. 526 pp.
Conservation Status
Rank Method Rank calculation - Biotics v2
Review Date2025-04-03
Change Date2006-02-03
Edition Date2025-04-03
Edition AuthorsCordeiro, J. (2006); rev. T. Cornelisse (2025)
Threat ImpactHigh
Range Extent20,000-200,000 square km (about 8000-80,000 square miles)
Number of Occurrences21 - 80
Rank Reasons
This species has a small to moderate range and number of known occurrences rangewide, but it is subject to many threats and there is evidence of long-term population declines, although short-term population trends are unknown.
Range Extent Comments
This species occurs in the northwestern United States in northern Idaho and northwestern Montana (RARECAT 2025; InvertEBase 2025).
Occurrences Comments
This species is known from at least approximately 29 occurrences using a 1 km separation distance and records from 1994-2025 (RARECAT 2025; InvertEBase 2025).
Threat Impact Comments
Exact threats to this species are unknown, but other terrestrial snails in the same habitat and range are known to be threatened by logging and grazing over most of known and potential range as well as increased fire frequency and highway construction (Frest and Johannes 1995; British Columbia Conservation Data Centre 2024).
Ecology & Habitat

Habitat

This species is found under woody debris and leaf litter or in downed rotten wood in mesic mixed conifer forest, including in riparian areas in forests (Hendricks et al 2012; British Columbia Conservation Data Centre 2024; InvertEBase 2025).
Terrestrial Habitats
Forest/WoodlandForest - Conifer
Palustrine Habitats
Riparian
Other Nations (1)
United StatesN3
ProvinceRankNative
MontanaS2Yes
IdahoS4Yes
Threat Assessments
ThreatScopeSeverityTiming
2 - Agriculture & aquacultureLarge (31-70%)Moderate or 11-30% pop. declineHigh (continuing)
2.3 - Livestock farming & ranchingLarge (31-70%)Moderate or 11-30% pop. declineHigh (continuing)
4 - Transportation & service corridorsRestricted (11-30%)Moderate or 11-30% pop. declineHigh (continuing)
4.1 - Roads & railroadsRestricted (11-30%)Moderate or 11-30% pop. declineHigh (continuing)
5 - Biological resource useLarge (31-70%)Serious or 31-70% pop. declineHigh (continuing)
5.3 - Logging & wood harvestingLarge (31-70%)Serious or 31-70% pop. declineHigh (continuing)
7 - Natural system modificationsRestricted (11-30%)Moderate or 11-30% pop. declineHigh (continuing)
7.1 - Fire & fire suppressionRestricted (11-30%)Moderate or 11-30% pop. declineHigh (continuing)
7.1.1 - Increase in fire frequency/intensityRestricted (11-30%)Moderate or 11-30% pop. declineHigh (continuing)

—

Roadless Areas (1)
Idaho (1)
AreaForestAcres
Bighorn - WeitasNez Perce-Clearwater National Forest254,845
References (9)
  1. British Columbia Conservation Data Centre. 2024. Element Subnational Ranking Form in Biotics 5 database. NatureServe, Arlington, Virginia.
  2. Burke, T.E. 2013. Land snails and slugs of the Pacific Northwest. Oregon State University Press, Corvallis. 352 pp
  3. Frest, T.J. and E.J. Johannes. 1995c. Interior Columbia Basin mollusk species of special concern. Final Report (contract #43-0E00-4-9112) prepared for Interior Columbia Basin Ecosystem Management Project. Deixis Consultants, Seattle, Washington. 274 pp. + tabs., figs.
  4. Hendricks, P. 2005. Surveys for animal species of concern in northwest Montana. Section 4: Terrestrial mollusk surveys in northwestern Montana; and section 5: Plum Creek owl and mollusk surveys. Unpublished report to the Montana Department of Fish, Wildlife & Parks, Montana Natural Heritage Program, Helena, Montana, May 2005. 53 pp.
  5. Hendricks, P. 2012. A guide to the land snails and slugs of Montana. A report to the U.S. Forest Service – Region 1. Montana Natural Heritage Program, Helena, MT. 187 pages + appendices.
  6. Hendricks, P., and B.A. Maxell. 2005. USFS Northern Region 2005 land mollusk inventory: a progress report. Report submitted to the U.S. Forest Service Region 1. Agreement #05-CS-11015600-033. Montana Natural Heritage Program, Helena, Montana. 52 pp.
  7. InvertEBase. 2025. Online. Available: https://invertebase.org/portal/index.php.
  8. <p>NatureServe's Rapid Analysis of Rarity and Endangerment Conservation Assessment Tool (RARECAT). 2025. Version: 2.1.1 (released April 04, 2025).</p>
  9. Turgeon, D. D., J. F. Quinn, Jr., A. E. Bogan, E. V. Coan, F. G. Hochberg, W. G. Lyons, P. M. Mikkelsen, R. J. Neves, C. F. E. Roper, G. Rosenberg, B. Roth, A. Scheltema, F. G. Thompson, M. Vecchione, and J. D. Williams. 1998. Common and scientific names of aquatic invertebrates from the United States and Canada: Mollusks. 2nd Edition. American Fisheries Society Special Publication 26, Bethesda, Maryland. 526 pp.