Brown Juga (snail) (Juga sp. 3 )

Close up of a Juga snail species with a dark-brown, cone-shaped shell.
Example of a Juga species. (
Category: Molluscs
Ecosystems: Riparian areas
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The brown juga is a freshwater aquatic gastropod. Their population size is considered low and the trend is unknown. Juga species generally require cold, clear, well-oxygenated water; they are sensitive to pollution, and intolerant of warm waters, low dissolved oxygen, or major seasonal fluctuations. Destruction of springs by grazing, logging, and water diversion, for such things as for water supply and fish hatcheries, has already caused extensive extinction of Juga species throughout western North America.

Description and Range

Physical description

Juga species are medium-sized, aquatic, gilled snails with tall conical shells. This genus (Juga) is part of the family Semisulcospiridae. The taxonomy of the Semisulcospiridaelike most freshwater gastropods, has been based largely on shell morphology, and the tremendous variation makes the current taxonomy problematic and species identification difficult. Current work using reproductive anatomy and DNA to help resolve some of the taxonomic problems will likely result in changes in taxonomy in the future.

Dozens of tiny, dark Juga species snails underwater clinging onto rocks in a stream.
Dozens of tiny Juga species snails clinging onto rocks in a stream. Bonnie Besijn - USGS Western Fisheries Research Center Bonnie Besijn - USGS Western Fisheries Research Center

Ecology and life history

Juga species are native to the streams and springs of the Pacific Northwest, California, and the Great Basin. The brown juga depends upon riparian habitat for its life requirements. It is found in low to medium elevation small spring-fed streams and springs, with cold, fast-flowing, well oxygenated water and gravel substrate. It is most frequently found in very small and shallow but perennial spring-fed streams and springs. They exhibit seasonal migrations both upstream and downstream.

Juga snails are characterized as rasper-grazers, feeding on both algae and detritus on rock surfaces and deciduous leaf litter.

The egg masses of Juga are most often found in loose (non-cemented) but stable cobble substrate, with free and fairly vigorous flow through at least the upper substrate layers. Most Juga species appear to breed and lay eggs once a year as adults. Egg masses are located under rocks in the spring, and eggs hatch in one month. Juga species live from five to seven years, reaching sexual maturity in three years, and can continue to grow.

Geographic range

Where found, Juga species can comprise over 90 percent of the invertebrate biomass in some streams.

The brown juga is rare, found only in a few of the central and eastern Columbia Gorge tributaries, Skamania and Klickitat Counties, Washington, and in Multnomah and Hood River Counties, Oregon. This species seems to be restricted in distribution in Washington to the Columbia River Gorge, which historically provided abundant springs for habitat.


This species is identified as a Species of Greatest Conservation Need (SGCN) under the State Wildlife Action Plan (SWAP). SGCN-classified species include both those with and without legal protection status under the Federal or State Endangered Species programs, as well as game species with low populations. The WDFW SWAP is part of a nationwide effort by all 50 states and five U.S. territories to develop conservation action plans for fish, wildlife and their natural habitats—identifying opportunities for species' recovery before they are imperiled and more limited.

Conservation Threats and Actions Needed

  • Fish and wildlife habitat loss or degradation
    • Threat: Water diversion; habitat loss to development.
    • Action Needed: Protect small spring-fed streams.
  • Resource information collection needs
    • Threat: Taxonomic uncertainty may mean one or more taxa are in greater decline.
    • Action Needed: Taxonomic clarification.

This species' climate vulnerability is assessed as "moderate to high." Climate vulnerability is a way to assess the degree to which a habitat or species is susceptible to, and unable to cope with adverse impacts of climate change.