Dear Trystan,

One of my favorite things to do is look at pond water with a microscope. I love to see all the teeny tiny critters zooming around in a single drop.

I talked about microorganisms, also called microbes, with my friend Claire Burbick. She’s a microbiologist at Washington State University. She told me the key trait for microbes is size. Microbes are micro—which means extremely small.

The most common microbes are bacteria, viruses, fungi and some parasites. Some microbes are just one simple cell. Some microbes are one complex cell. Other microbes are made of many cells. There are even microscopic animals like water bears, gastrotrichs and eyelash mites.

Image by Herney Gómez from Pixabay

Another word that starts with micro is microscope. Microbes are so tiny that your eyes need help to see them.

“For bacteria, we can use our normal microscope,” Burbick said. “But for viruses, we use even stronger microscopes like electron microscopes. They can make something tens of thousands of times bigger.”

Scientists measure bacteria in micrometers, also called microns. If you cut a meter stick into one million pieces, a micrometer is the size of one piece. One cell in your body is about 50 micrometers wide. A strand of silk from a spider web is about 5 micrometers thick.

Viruses require an even smaller unit called nanometers. To get a nanometer-sized piece, you’d need to cut a tiny micrometer into one thousand pieces. So, that same strand of spider silk is 5,000 nanometers thick. One particle of the COVID-19 virus is about 80 nanometers wide. Believe it or not, there are about 10 million viruses in one drop of seawater.

Image by Robert Owen-Wahl from Pixabay Image by WikimediaImages from Pixabay

But wait. Fungus is a microbe. You might wonder why you can see fuzzy mold on last week’s sandwich. Some microbes like bacteria and fungi live in groups called colonies.

“We can see the big colonies forming or the fluffy stuff on your old bread,” Burbick explained. “But if we want to see what they really look like, we have to go microscopic to get the detail.”

Some microbes are pathogenic. They can cause disease. That’s why we wash our hands and wear masks.

But our bodies are teeming with microbes that help us—or at least don’t bother us. Some help us digest food. Some help our immune systems keep us healthy.

For every cell in the human body, there are ten microbes living on us or inside us.

“We are hand in glove with this very tiny world,” Burbick said. “We’re kind of like planets with all these little microbes living on us.”

Keep spinning, you beautiful planet.


Dr. Universe (and all my microbes)