Water We Talking About? A Pennsylvania Pond Infested with “Fleas”

We realize we’ve all lost track of time as we continue to flatten the COVID-19 curve but, trust us, it’s Friday. And that means it’s time for Water We Talking About? Kids have questions and we track down a scientist with an answer. Today’s is a first – William and Luke sent a video of some mysterious creatures from a Pennsylvania pond.

The Question:

We are raising bullfrog tadpoles that we scooped out of our pond in Pennsylvania, but we just noticed these creatures floating around today, a day after setting up our new ecosystem. Do you know what they are?

William, Age 8, and Luke, Age 6 – Sarver, Pennsylvania


The Answer:

Hi William and Luke. Thanks for being our first-ever Water We Talking About? participants from outside of Wisconsin! We hope your tadpole raising is going well and are excited that you shared this mystery with us. As you probably know, lakes, ponds and streams are just full of life and, while the little critters you found are tiny, they play a huge role in freshwater ecosystems. We sent your video to our graduate student, Mike Spear and here’s what he had to say.

Mike Spear
Mike Spear.

Thanks for the cool video, guys! It is hard to tell you exactly what you’re seeing without a microscope, but these critters are likely a kind of zooplankton called Cladocerans, also known as “Water fleas” because when they swim they appear to take tiny little jumps like fleas.

Zooplankton are tiny little animals that float, swim (and jump) throughout the water column and they play an important role in the food web – especially for all of the fish that like to eat them.

Water fleas eat many kinds of bacteria and smaller plankton, including algae and can help keep water bodies (including your tadpole tank!) clear. Cladocerans are part of the Crustacean class, which also includes animals like shrimp, crabs, and lobsters. – Mike

We will go on to say what people who regularly read this blog already know – “water fleas” are some of our absolute favorite animals in our lakes, especially a kind called Daphnia.

Daphnia pulicaria.

Here in Madison, Wisconsin, we are approaching a time in spring when our lakes enter what we call “clear water phase” and the water in the lakes gets so clear that you can see right down to the bottom (which, trust us, is NOT how our water usually looks).

Anyway, the reason the water gets so clear is because the temperature and other conditions in the lake get just right for a species of Cladoceran named Daphnia pulicaria. When that happens the populations of daphnia in our lakes get huge and we have million upon millions (if not billions) of these tiny little water fleas eating any algae they can find. They eat so much algae that they totally clear the water column and the entire lake suddenly looks like a picture from a beach in the Bahamas. (Well, except there are no palm trees or coral reefs, but you get the picture!)

We bet that lakes in Pennsylvania will soon be entering their clear water phases (ours usually starts around mid-May) so be on the lookout for that. And good luck growing your tadpoles!

Lake Monona in Madison, Wisconsin during clear water phase. Photo: Hilary Dugan

That’s it for this week! Thanks for tuning in everyone. Next week’s big question: Lukas wants to know if we have freshwater jellyfish in Wisconsin. And, if so, are they dangerous?

If you’re a kid with a question of your own, ask us at media@limnology.wisc.edu – @WiscLimnology on Twitter – or our Center for Limnology Facebook Page!