The body size of insects is evolving in urban zones. Researchers in Belgium found the water flea’s (Daphnia magna) city variant was 44 percent smaller than its rural cousin. Larger forms of this water ...

A type of zooplankton, Daphnia pulex (a.k.a. the water flea) is a microscopic crustacean whose unique reproduction habits make it the perfect species for studying evolution and natural selection.