An invasive snail is being blamed for killing hundreds of waterfowl on the Upper Mississippi River this fall. Field workers have found almost 1,000 dead coot and lesser scaup washed up on the shores near Genoa since early October, according to the U.S. Fish and Wildlife Service. The birds are believed to be the victims of an intestinal parasite found in faucet snails, which the birds eat during stopovers on their fall migration. Die-offs have become an annual event during the past 15 years, since the arrival of the faucet snail.