Killer shrimp are invading UK waters and raising concern among scientists. Killer shrimp may threaten the balance of life in fresh-water ecosystems.On Sept. 9, Britain's Environment Agency issued an alert that "killer shrimp" were spotted in a fresh-water reservoir in Cambridgeshire, England. Before you have a 28 Days Later moment, take a deep breath. These tiny crustaceans, the Dikerogammarus villosus shrimp, which can grow up to 3 centimeters (about 1 inch) in length, pose no direct danger to humans. But the killer shrimp is bigger than local species – and more aggressive. The "killer shrimp" eats other shrimp and small...