- [Narrator] Hello, my little crayfish friend.

These fresh water lobster lookalikes are all over the south, even in some of the nastiest waters.

- Boy, oh boy, I have seen cray fishes in some pretty disgusting waters.

- [Narrator] How they manage to live in those waters is a mystery.

But Bronwyn Williams, our resident crayfish expert, says the tiny worms that live on crayfish could be helping.

- There's one.

Oh, hey, little dude.

Okay, so they have an adhesion point.

They're butt sucker.

I could say that.

That they use to attach to the crayfish.

- [Narrator] Crayfish worms are completely dependent on crayfish for their reproduction.

- They actually need to deposit their cocoons with live embryos onto a living crayfish in order for that embryo to develop and then hatch into a worm.

- [Narrator] And what does the crayfish get out of this?

- What we see in the digestive tract to these crayfish worms, they are grazers for the most part.

So you'll find diatoms and algal material, anything that would really land and settle on that surface of the crayfish.

So they're effectively cleaners.

The crayfish is that I've collected that are just the most fouled, just have the most sediment all over them, and even packed into the gill chambers.

I don't find a single worm on them.

So cause and effect.

Obviously, I mean, that's anecdotal.

- [Narrator] Worms aren't even the only animals living on crayfish.

They're also home to these little shrimp-looking things called ostracods, which seem to live in perfect harmony with the crayfish worm.

And unlike other ostracods, this species has developed claw-like hooks, presumably to latch to the crayfish's shell.

So one crayfish literally contains multitudes.

- [Bronwyn] You can think of crayfish as ecosystems all on their own.

Also, here's a baby crayfish.

You're welcome.