Category Archives: Biology

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!

Giant Squid!

Giant squid (Architeuthis dux) are rare deep-sea invertebrates, which are known mostly through dead specimens that have floated to to surface, washed up on beaches, or met an untimely end in the stomach of a sperm whale. Excitingly, the first video footage shot by humans of a live giant squid swimming at depth (around 900 m below the surface) was filmed earlier this year, and while a snippet has already hit the internet, the full footage is set to air Sunday evening on the Discovery channel (and has been broadcast on a Japanese television program). The short clip that’s already been released shows a graceful creature, gliding in a pitch-black, seemingly empty, ocean. A shot of its body shows its huge eye looking, if I can anthropomorphize the squid for a moment, almost baleful. (Though if I were swimming along in the deep ocean and were suddenly confronted with a submarine with lights, I’d probably look pretty baleful too.)

Giant squid are the world’s second largest largest invertebrates (behind the colossal squid), reaching up to 13 m in length. Much of this length is in the two hooked tentacles it uses to hunt, though there is no part of the giant squid that is not outsized. The tentacles can grow up to ~ 8 m, the arms are a comparatively puny ~2 m, the mantle (ie, the body) can be up to 2.25 metres long.

Giant Squid diagram

Artist’s rendition of a giant squid. Squid is broadly, but not at all rigorously, to scale.

The eyes are huge too, with a diameter approaching that of a dinner plate. The eyes, like much of the squid’s anatomy and behaviour, is still somewhat of a mystery: virtually no sunlight penetrates down to the depths that the squid lives at, so why does the squid for such a huge eye? It takes an enormous amount of energy to develop such a huge eye, and if there’s no light to be seen, that energy seems like a waste. One of the leading theories is that the eyes are used to detect the light from bioluminescent creatures, especially when they’re dispersing in the path of a sperm whale.

For more on the anatomy and behaviour of the giant squid, it’s hard to do better than this post from Deep Sea News. They also have an excellent link round-up of all things giant squid.

But its impressive physical qualities have enchanted not only scientists and admirers of weird marine creatures; the giant squid has a giant tentacle in the world’s marine lore. The giant squid lives in all the oceans, and is often thought to be the inspiration for the kraken. It’s huge, fearsome (it has hooks on the tentacles!), and lives in a murky world that we have only just started to be able to explore. It’s not surprising that these creatures are cast as the villain in sea-lore, but it’s not like the giant squid is a single-minded creature out for blood. Sure, I wouldn’t want to be on the wrong end of its beak, but I wouldn’t want to be on the wrong end of a killer whale or a leopard seal either. Yet we have children’s movies about orcas, and footage of a leopard seal gently trying to teach a photographer how to hunt penguins was all over the internet a while back. We don’t treat either of them as capital-m Monsters, so why the giant squid? It’s not even at the top of its food chain — while the image of the giant squid and the sperm whale struggling and fighting is culturally pervasive, in reality, the squid doesn’t stand much of a chance against the whale. I have a suspicion that some of the giant squid’s reputation is due to it being an invertebrate: to a vertebrate, land-dwelling species, squids are profoundly weird looking creatures. When humans first came across the giant squid, say in their fishing nets, there was probably not that much context handy for the sailors to make sense of these huge, intimidating creatures. We don’t have much contact with them — we’re only just getting footage of them in their natural habitat! — and we haven’t had time for any sort of image rehabilitation to take hold culturally. This video has gotten a lot of press so far, so it’ll be interesting to see how, if at all, it starts to change our collective perception of these elusive, strange creatures. I’ll update this post when I can find a video of the full Discovery Channel show.

In the mean time, if you’re interested in watching a dissection of a giant squid, the Museum Victoria in Australia has video of the dissection of a giant squid caught in a fishing net off Australia in 2008. It’s long, but the scientists go through the squid’s anatomy in some detail, and it’s well worth the time.

Duhn-nuh duhn-nuh duhn-nuh duhn-nuh Hagman!

Sometimes it seems like it’s only a matter of time before the hagfish comes up for discussion, though at least one person thinks that I may be, and I quote, “vastly over-estimating the market saturation of hagfish blogging.” Perhaps it’s a holdover from that one seminar talk I went to when I was in undergrad given by a professor who researched (among other things) the properties of hagfish slime. While he was talking my friend drew a quick sketch of Hagman, the hagfish superhero, and we all snickered loudly in the back row. Hagman then sporadically came up in conversation for weeks afterward, and still makes me snicker several years later.

Zorro-esque Hagman vs. Niklas Hagman the NHL Left Winger

Hagman fights for truth, justice, and the Stanley Cup.

There’s a good reason that hagfish are one of those creatures that gets a disproportionate amount of cultural presence, and that’s because they’re weird and gross. They’re marine invertebrates, living mostly at great depth in the ocean, burrowing into dead whale carcasses and other rotten corpses and eating their way out. They have no bones or jaws, but intimidating rings of scaly teeth. And when they’re attacked or startled, they produce a cloud of slime, tie themselves in a knot, shimmy out of the slime cloud that’s now engulfed the attacker, and escape.

That’s an impressive trick, disgusting table manners or no.

Hagfish slime is astounding. The mucus the hagfish produces is a milky white goo, and while it doesn’t produce much mucus at any one time, a small amount of mucus quickly turns a large container of water into a large mass of slime.

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