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.
â¢ Had to have a microscope first. o Invented in 1595 by Zacharias Janssen  Was considered a toy for the rich. â¢ Anton Van Leeuwenhoek 1670âs o Improved the microscope so much heâs considered the father of the microscope. o First looked at water under a microscope o Discovered small animals.