What was the source of the microscopic animal kills described by Leeuwenhoek?

The microscopic animal kills described by Antonie van Leeuwenhoek were primarily attributed to a type of microorganism known as "animalcules," which he observed in various water samples. He noted that these tiny creatures, including protozoa and bacteria, could be harmful to other microscopic organisms, leading to their deaths. Leeuwenhoek's observations laid the groundwork for understanding the role of microorganisms in ecosystems, including their potential as pathogens. His meticulous studies highlighted the complex interactions within microscopic life forms.