Today in Weird Invertebrates: Lawn Crayfish

Since I live in the Great White North, which is not generally known for its peculiar fauna, I had never heard of burrowing crayfish. I owe my newfound knowledge to Ursula of Kevin and Ursula Eat Cheap, who also hadn’t heard of such a thing until she found one hanging out in her lawn. (link goes to the episode of their hilarious, if occasionally surreal, podcast where she scolds the state of North Carolina for not putting “We have lawn crayfish!” on their roadsigns.) So, since one of my missions in life is to learn all there is to know about weird invertebrates, I did some digging about the burrowing crayfish.

There’s not an awful lot of information about burrowing crayfish online, and much of the google hits are people going “I think there’s a crayfish… in my lawn?!” (To be fair, that is precisely what I’d do were I in that situation.) Interestingly, most of the papers I found about them make a comment about their life cycle or ecological existance being poorly understood. Perhaps this says more about me than about wetland biologists, but were I a field biologist, burrowing crayfish’d be near the top of my list of research subjects.

Crayfish anatomy

The cray(on)fish. Roughly but not rigourously to scale.

Here’s what I’ve found about them. There are several species of burrowing crayfish, in both the Cambaridae and Parastacidae families. The former live in the southern US, while the later live in the Tasmania and the damper parts of Australia. Their life cycles seem to be similar to most crayfish, hatching from eggs stuck to their mother’s underside, and as they grow they molt. Like all crayfish, they have two large claws, four pairs of walking legs, and several pairs of swimming legs. They range in size from a few centimeters to a few inches (Ursula estimated the one in her yard was about five inches long), and their colour varies between species from bright red to bright blue. Ursula also said something about them glowing under ultraviolet light, but I can’t find anything confirming that. If you have a lawn crayfish and a black light, please investigate and report back!

Like all crayfish, burrowing crayfish eat anything they can get their claws on, including roots and dead plant matter in and around their burrows. Some species stick around in their burrows for food, while others are more likely to go foraging outside.

The burrowing crayfish live where there is a high water table, and often near sources of surface water. They dig complex burrows with branching paths and multiple sections, and usually at least part of the burrow sits below the water table. As they excavate the burrow, they drag mud and dirt up to the surface, and sometimes form a chimney at the mouth of their burrow. What’s not clear to me is how, exactly, they dig out their burrows. Their claws are well adapted for nabbing dinner, warding off predators, and defending territory, but they don’t look like very efficient shovels. On top of that, I’ve no idea how they’d transport the dirt up from the bottom of their burrow up to the top, let alone make a chimney out of it — maybe they shove it along with their tails? Or maybe the claws are shaped to be at least semi-efficient shovels? I’ve found no satisfactory answers, so if you’ve got an idea, please, leave it in the comments.

Crayfish with backpack

Perhaps they’ve developed backpacks to haul the dirt to the surface.

While the numbers are far from clear, since many burrowing crayfish species are poorly studied, it seems like burrowing crayfish are more threatened ecologically than other species of crayfish, and several are critically endangered. Unfortunately, many of the google hits for burrowing crayfish pertain to how best to get rid of lawn crayfish, because they can do a lot of aesthetic damage to a lawn. As water use shifts and water tables lower, however, their available habitat may shrink significantly. Hopefully, researchers will get some more concrete numbers and answers about burrowing crayfish before they suffer more habitat and population loss.

Crayfish, master of simple machines

Or maybe they use a pulley system!

5 Responses to Today in Weird Invertebrates: Lawn Crayfish

  1. How, how in over a decade of invert-obsession, did I not know about this?!? And on a related note, I will now never walk barefoot through the grass in the south.

  2. Am part of a team that has been studying the piedmont blue burrower for some years. I think they are so poorly studied, not because of disinterest but because they are difficult to study. I think they operate like a bulldozer, using claws to form mud balls and then push it out of the burrow. Part of our team, at Auburn University, have built crayfish habitats that look like big ant habitats…a thin layer of soil between two panes of glass or plexiglass. So they have seen how they dig their burrows.

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