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.
At this time, Dutch spectacle makers were experimenting with multiple lenses. Telescopes were invented in this way. By reversing a telescope the microscope was discovered! Credit for the first microscope is usually given to Zacharias Jansen in Middleburg, Holland around 1595. The Jansen microscope was composed of 3 sliding tubes, measuring 18 inches long when fully extended and 2 inches in diameter.