<human>:  Why is it that viruses are so small?
<bot>: The smallest known virus is the bacteriophage phi6. It’s about.1 micrometers in size. The reason viruses are so small is because viruses have evolved to exploit the tiny spaces inside cells, where there is a lot of room for them to fit. They do this by taking advantage of the host cell’s machinery, which makes up most of the cell’s volume.