What insect spreads the bacteria that causes plague from rats to humans?

The correct choice is that fleas are the insects responsible for spreading the bacteria that causes plague from rats to humans. The primary vector for the bacteria Yersinia pestis, which is responsible for plague, is the flea, particularly the Oriental rat flea (Xenopsylla cheopis). This flea bites infected rodents, such as rats, and becomes contaminated with the bacteria. When the infected flea bites a human, it can transmit the bacteria, leading to infection.

Understanding the role of fleas in this transmission process is crucial for recognizing how plague outbreaks can occur, especially in areas where rodent populations are prevalent. While other insects like mosquitoes and ticks can transmit various diseases, they do not play a role in the transmission of plague. Ants, on the other hand, are not vectors for any diseases affecting humans in the same context. Recognizing the specific vectors for diseases helps in developing effective control and prevention strategies.