Invasion of the Rusty Crayfish | Bleader

Invasion of the Rusty Crayfish



I’ve never seen so many claws.

They’re all over Chicago beaches, scattered amid other refuse that’s washed up—blue or red-tinted claws that range from half an inch to three or more inches long.

I mean, some of them aren’t tiny. Some of them appear capable of tapping me on the shoulder and asking for a bite of my sandwich. Those pincers could fit around one’s toes, or fingers, or—well, anyway, they’re bigger than anything most of us would expect to encounter in Lake Michigan.


I knew the lake had crayfish. I grew up on the Michigan side, and as kids we used to catch them all the time in shallow, rocky areas. Some people used them as fish bait. My friends and I just thought it was cool to pick them up and watch them wave their claws around. We had a lot of time on our hands.

But those critters were rarely more than a couple inches long altogether. And I’ve never seen significant numbers of claws washed up on shore.

In fact, it’s not just the claws. Once I started looking closely this spring, I came across other body parts—shells, antennae, even legs, like armor that’s been discarded after an invasion.


It turns out that isn’t far from the truth. Kurt Hettiger, an expert on lake ecology at the Shedd Aquarium, said the creatures are rusty crayfish, an invasive species from the Ohio River valley.

Though fishermen brought them to the Great Lakes decades ago, their numbers around here appear to be growing. Their appetite for plants, fish eggs, and small fish is probably lowering the population of some native species, including other, smaller crayfish. You can read all about them here.

“You find them in every lake and river around here now,” Hettiger said.

He said it makes sense that beachgoers might come across their claws or shells. “They regularly molt—just like a snake that sheds its skin. They start growing and the carapace splits from underneath them and from on top, and they come out and they’re soft.”


And then they grow new shells. This happens a couple of times a year.

If a claw breaks off along the way, no biggie—they can grow back as well.

Hettinger said others had told him they’d seen a lot more claws on shore this year, but he wasn’t sure why. “I haven’t heard anything specific, but the past few weeks of weather, the wind is coming out of the east, probably washing up a lot of stuff that usually doesn’t wash up on shore,” he said. “What you’re probably seeing is that the winter was a little harsh and lots didn’t make it.”


In case you're wondering: Based on my memories of being 11, it can smart to get pinched by a set of crayfish claws. But those creatures don't want anything to do with you.