We regret to inform you that the snails are not always good. Sometimes, they're hosts to parasites that feast on the blood of adorable ducklings.
Remember that viral photo of the cute little ramp Washington D.C. made to give ducks easy access to the Capitol Reflecting Pool? Around 80 ducklings are dead in the nearby Lincoln Reflecting Pool.
It's a heartbreaking turn of events.
But before you start cranking up the voltage on your snail-zappers, it's important to remember that there is more to every snail-story than meets the eye.
The NPS says that necropsies of the ducklings revealed the cause: A parasite that develops and grows in snails that live in the pool. Officials I spoke with via email weren't sure of the specific name of the parasite—I've asked the researchers at the USGS National Wildlife Health Center, who performed the necropsies, and will update when we hear an answer—but as parasites that harm duck populations go, a good bet would be on the same invasive species that lives in faucet snails, which damaged duck populations in the Upper Mississippi in 2008 and 2016.
After the snails are infected by the parasite, ducks eat the snails, and then the snail-hosts bore into the ducks' intestinal walls, as Jim Nissen at the Fish and Wildlife Service told NPR: "They gorge on blood and then lay eggs. The eggs are passed through the birds' feces, and that's how they reach the snails. That's how the cycle is perpetuated."
So, the snails aren't really the bad guys here. They're just an unwitting host to a parasite that drinks blood and hates fluffy baby ducks.
"We don't know the reason for the elevated levels of the parasite, and likely never will," Michael Litterst, Chief of Communications at the NPS told me via email. "We had a three day stretch of temperatures in the 90s that ended the day before the first ducks died, so it is possible that was a contributing factor."
In order to stop the spread, they'll need to drain the pool. This is the first time that the pool has been drained for parasite-related reasons. NPS hopes to have the thing scrubbed down for refilling to begin by June 16.