Utilities Staff Using Detective Skills to Find Invasive Snails

Mudsnail
A utilities staff member collects a water sample on the north fork of Meydenbauer Creek.

Despite stormy skies and cold temperatures Utilities’ stream experts have been on the lookout for signs of the New Zealand Mudsnail – tiny invaders that can take over the ecology of our streams hurting native species like trout and salmon. Staff have been looking for snail DNA in area streams to see if the invaders are spreading. The snails were first detected in Kelsey Creek, Bellevue in 2012.

New Zealand Mudsnails are very small, less than 1/8 inch, and are dark brown. They are very difficult to see when in low numbers. While snails don’t have fingerprints, they do shed skin cells and their waste into the water. This leaves traces of DNA that can be detected, just like TV crime shows. The process is known as environmental DNA tracing or eDNA. Utilities staff are working with Washington State University (WSU) to evaluate every stream for their presence. They start by collecting and filtering water samples from each stream. WSU analyzes the filters for unique genetic markers produced by New Zealand Mudsnails. Using eDNA is cheaper and quicker than doing visual surveys, though it isn’t meant to totally replace visual surveys. Bellevue is one of the first cities in the nation to use these techniques as a management tool to help slow the spread of invasive species.

What is so bad about a little snail? New Zealand Mudsnails quickly reproduce by cloning, so it only takes one small snail to produce up to 2 million snails in just a couple of years. They are bullies, displacing the good native invertebrates at the bottom of the stream. The snails have a tight operculum (“trap door”) that protects them from drying out. It is so strong that they can survive being eaten by trout, causing the fish to starve while not harming the snail! Bleach does not work to kill them.

What do we do with the information? We inform people living along the infested streams about the potential for spreading the snails. The city also posts signs and requires any contracts to include more intense decontamination procedures so our consultants and contractors do not move the snails to other areas.

What can Bellevue residents do?

  • Avoid getting into infested waters. Don’t allow dogs to get into multiple streams, such as at Kelsey Creek Farm.
  • Clean all boots and shoes with Formula 409 Degreaser, then rinse with water (the degreasing agent can penetrate the snail’s “trap door.”)
  • Get more information at www.bellevuewa.gov/new-zealand-mud-snails.htm.

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