Teens Make a Big Microscopic Discovery

On a rainy autumn day, a group of students gathered in a damp cemetery in Denmark. Carefully, they peeled moss and lichen—fuzzy green colonies of algae and fungus—from trees and gravestones. Then they placed these samples in coffee filters. The teens were searching for strange little animals living in the moss and lichen: tardigrades.

It was a rainy autumn day in Denmark. A group of students met in a damp cemetery. They searched for moss and lichen, fuzzy green colonies of algae and fungus. Carefully, they peeled them from trees and gravestones. Then they placed these samples in coffee filters. Strange little animals live in the moss and lichen, and the teens were looking for them. The animals are tardigrades.

Tardigrades are tiny, chubby invertebrates, or animals without a backbone. They’re so small that they’re practically invisible to the naked eye. Under a microscope, they look a bit like gummy bears—but with daggerlike teeth, long claws, and eight legs! Because of their appearance, tardigrades are sometimes called “water bears” or “moss piglets.”

Two years ago, a group of scientists set out on a mission to document the various tardigrade species living across Denmark. So they enlisted nearly 30,000 kids and teens to help. “I was excited and fascinated to look for tardigrades,” says Johanna, a 19-year-old who participated in the project as a high school senior. “I didn’t think we would find any.” But it turned out that the mosses and lichens she and other students collected were teeming with these teeny creatures—including a handful of previously unknown species!

Tardigrades are tiny, chubby invertebrates. These animals don’t have a backbone. They’re almost too small to see with the naked eye. Under a microscope, they look a bit like gummy bears. But they have sharp teeth, long claws, and eight legs! Tardigrades are also called “water bears” and “moss piglets” because of their appearance.

Two years ago, a group of scientists began a project. They wanted to document the different tardigrade species in Denmark. So they got nearly 30,000 kids and teens to help. Johanna helped with the project as a high school senior. “I was excited and fascinated to look for tardigrades,” says Johanna, now 19. “I didn’t think we would find any.” But she and other students collected mosses and lichens. And their samples were full of these tiny creatures. They even collected a few previously unknown species!

Tardigrades are really, really small—most are less than 1 millimeter (0.04 inches) in length (see “Zooming In”). That’s just a little larger than the period at the end of this sentence. Despite being so tiny, this animal is extremely tough.

Tardigrades prefer to live in damp places, so they’re usually surrounded by a thin layer of water. The moisture prevents them from drying out and allows oxygen from the water to pass into their body. But if water becomes scarce, tardigrades don’t die. Instead, they enter a dormant, or sleeplike, state. They pull in their limbs and shrivel up into a ball. They stop needing food or water. Their bodies release a flexible molecule that pads their insides like protective bubble wrap.

Tardigrades are really, really small. Most are less than 1 millimeter (0.04 inches) long (see “Zooming In”). That’s just a little larger than the period at the end of this sentence. This animal may be tiny, but it’s extremely tough.

Tardigrades like to live in damp places. A thin layer of water usually surrounds them. The water keeps them from drying out. It also allows oxygen from the water to pass into their body. But if water runs short, tardigrades don’t die. Instead, they become dormant. They enter a sleeplike state. They pull in their limbs and shrink into a ball. They stop needing food or water. And their bodies release a flexible molecule. It pads and protects their insides like bubble wrap.

In this dormant state, tardigrades can survive almost anything. “They can freeze. Get really hot. They can live without oxygen,” says Martin Sørensen. He’s a biologist at the Natural History Museum of Denmark who worked on the study to document tardigrades across the country. Scientists have shot the creatures out of a gun, boiled them, and even sent them to space (see “Tardigrades Blast Off”). “As soon as you pour water on them, they liven up again!” says Sørensen.

Tardigrades are found everywhere on Earth—from the bottom of the ocean to high up in the mountains. They live in cold, icy regions and in boiling hot springs. But their favorite environment is the moist mosses, lichens, and soil in your backyard! “You don’t have to travel far to find them,” says Sørensen.

Tardigrades can survive almost anything in this dormant state. “They can freeze. Get really hot. They can live without oxygen,” says Martin Sørensen. He’s a biologist at the Natural History Museum of Denmark. He worked on the study to document tardigrades across the country. Scientists have shot tardigrades out of a gun and boiled them. They even sent them to space (see “Tardigrades Blast Off”). “As soon as you pour water on them, they liven up again!” says Sørensen.

Tardigrades live everywhere on Earth. They’re at the bottom of the ocean and high in the mountains. They live in cold, icy places and in boiling hot springs. But their favorite environment is right in your backyard! They love the moist mosses, lichens, and soil there. “You don’t have to travel far to find them,” says Sørensen.

A few years ago, a group of biologists, including Sørensen, partnered with Astra, the National Center for Science Education in Denmark, which runs a project called Mass Experiment. Every year, Mass Experiment conducts a different citizen science project in Denmark. The organization reaches out to schools across the country to get students’ help in collecting data. One year, students studied people’s recycling habits. This year, they are studying soil health. And in 2023, Mass Experiment had students search for tardigrades.

A few years ago, Sørensen and other biologists teamed up with Astra. That’s the National Center for Science Education in Denmark. It runs a project called Mass Experiment. Every year, Mass Experiment conducts a different citizen science project in Denmark. The organization contacts schools across the country. It asks students to help collect data. One year, students studied people’s recycling habits. This year, they’re studying soil health. And students searched for tardigrades for Mass Experiment in 2023.

Tens of thousands of students received instructions for how to collect samples of tardigrades’ habitats—or natural homes. They recorded each sample’s location in an app, along with a description of the surface on which it was found, like a rock, tombstone, or oak tree. Back in the classroom, the students placed the samples under microscopes and searched for water bears. They tried to classify tardigrade species by looking for identifying characteristics—like whether they had whiskers, the shape of their legs, and the animals’ eye color. Then students sent the samples to the Natural History Museum of Denmark to confirm their findings.

Like the students, the museum’s scientists could identify some tardigrades just by looking at them. But other species weren’t distinguishable based on appearance alone. Fortunately, the researchers had another tool they could use: DNA. This molecule carries hereditary information that contains the instructions organisms need to develop and function. The scientists examined the DNA collected from the tardigrades and were shocked by what they discovered. “In many of the moss and lichen samples, they found new species,” says Lene Christiensen, project manager for Mass Experiment. “It was a total surprise to everyone.”

Tens of thousands of students received instructions. They learned how to collect samples of tardigrades’ habitats, or natural homes. They recorded each sample’s location in an app. They also described the surface it had come from. That might be a rock, tombstone, or oak tree. Then the students went back to the classroom. They placed the samples under microscopes and searched for water bears. They tried to identify tardigrade species by their features. For example, they looked for whiskers, leg shape, and eye color. Then they sent the samples to the Natural History Museum of Denmark to check their findings.

The museum’s scientists could identify some tardigrades by appearance, like the students had. Other species were impossible to tell apart just by looking. But the researchers could use another tool. It was DNA, a molecule that carries hereditary information. It contains the instructions for organisms to develop and function. The scientists examined the tardigrades’ DNA, and they were shocked. “In many of the moss and lichen samples, they found new species,” says Lene Christiensen, project manager for Mass Experiment. “It was a total surprise to everyone.”