River otters primarily eat fish. They are also known to eat whatever is easiest to find, like crustaceans, mollusks, insects, birds, oysters, shellfish, crabs, crayfish, frogs, rodents, turtles and aquatic invertebrates.
1667: Robert Hooke 's famous Micrographia is published, which outlines Hooke's various studies using the microscope. 1675: Enter Anton van Leeuwenhoek, who used a microscope with one lens to observe insects and other specimen. Leeuwenhoek was the first to observe bacteria. 18th century: As technology improved, microscopy became more popular among scientists. Part of this was due to the discovery that combining two types of glass reduced the chromatic effect.
When the microscope was invented around 1590, suddenly we saw a new world of living things in our water, in our food and under our nose. But it's unclear who invented the microscope. Some historians say it was Hans Lippershey, most famous for filing the first patent for a telescope. Other evidence points to Hans and Zacharias Janssen, a father-son team of spectacle makers living in the same town as Lippershey.