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18 Awesome Facts About Giant Isopods

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There are 20 known species in the genus Bathynomus;  B. giganteus, or the giant isopod, is the biggest. Yes, they're kind of creepy looking. But they're also kind of cute! Here are a few things we know about these Internet-beloved creatures.

1. They’re not bugs.

They’re crustaceans, and are closely related to marine crustaceans like shrimp and crabs, and terrestrial crustaceans like the pillbug (Armadillidium vulgare).

2. They’re bottom dwellers.

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Giant isopods live between 550 to 7020 feet deep (and potentially deeper), and prefer a mud or clay floor, which they burrow into for shelter. “Bathynomus giganteus is more of a coldwater species,” says Dee Ann Auten, an Aquarist II at the Aquarium of the Pacific, which has four giant isopods in its Wonders of the Deep gallery. “They live in the Pacific Ocean, off Japan and in the South China Sea. That’s the kind of area where you would find them.”

3. They get big. Really big.

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Typically, giant isopods are between 7.5 and 14.2 inches in length, but they can get much bigger: One specimen pulled up with an ROV in 2010 was 2.5 feet long. Scientists aren't quite sure why these isopods get so enormous, but believe that their huge size might be an adaptation that helps them survive the extreme pressure of the deep ocean.

4. They come in different colors.

The giant isopod shell—which is comprised of overlapping segments—comes in two varieties: brown and pale lilac.

5. They’re carnivores.

Though they’re generally believed to be scavengers, feasting on dead animals that fall from above, some evidence suggests that they might also eat slow-moving live animals like sponges. Giant isopods also attack trawl catches.

6. They can go a very long time without eating.

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One giant isopod in Japan went for five years without eating a single bite before dying earlier this year. Auten attempts to feed her giant isopods every day, a ritual that requires a lot of patience. “The trick is what to feed them and how to eat them,” she says. “Here at the Aquarium of the Pacific, the hit is mackerel. It's usually what I feed them. I’ll butterfly a dead mackerel so that the insides are coming out, and then I will present it in front the isopod. I try offering food once a day and that's just because one day they might not be active as much, and one day they could be really hungry and I might miss that opportunity.”

All four of the giant isopods Auten cares for have eaten within the last year (Auten keeps track of who’s who based on the spines that are missing from their tails).  “One of them ate twice last year, one of them ate four times last year, one of them ate almost ten times last year. Another one I think was seven times,” she says. “It's fascinating and it's rewarding when you put so much effort into taking care of them and a lot of patience and you finally figure out this what they like to eat.”

7. But when they do eat, they gorge themselves.

Giant isopods have four sets of jaws—which are adapted to cut and tear at prey—and they get a workout when the animals are hungry. “When they're hungry and they're eating, definitely have a lot of food around them, because they'll keep eating,” Auten says. “They'll eat a lot at one time and then they can go for a long time without eating. There’s a comic of one giant isopod eating a dead whale, and it eats the whole thing except for the bones. It's sitting on its back like ‘ughh I'm full now.’ That's totally true! If they eat, they eat a lot.” In fact, they eat so much that they compromise their ability to move.

Still, they’re not aggressive feeders. “I've never had [an occasion] where they all ate at once,” Auten says. “I will make sure to bring enough food for all of them but whenever I feed them, it's one will eat at that one setting. They definitely would not fight.” And apparently, they’re not picky: Three giant isopods collected in the southern Gulf of Mexico had ingested large quantities of plastic.

8. They live in a constant state of semi-hibernation.

Since meals in the deep sea can be few and really far between, giant isopods limit their energy expenditure. “They have a slower metabolism,” Auten says. “Their bodies mechanics are like that because they're deep sea creatures and don’t find food all the time. So they're able to slow down their metabolism and energy level so they can survive. Watching ours, you can see they do that. They don't move around that much. They only ever move around when I'm trying to feed them. Normally they're just sitting there.”

9. They have something in common with cats.

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And it’s all in the eyes. Giant isopods have widely spaced, fixed compound eyes with more than 4000 individual facets. Cats and the crustaceans (and many other animals) have a reflective layer at the back of the eye called the tapeum, which reflects light back through the retina and increases the ability to see at night. It’s also what makes cats' and isopods' eyes appear to glow.

10. They probably don’t see all that well...

It’s pretty dark where isopods live, so, according to Auten, vision isn’t really a factor for them, or many other deep sea animals. “They use other senses to maneuver, to communicate, to find food, to find a mate,” she says. “I've done experiments with my flashlight to see if the isopods sensed a difference in light or anything like that. They don't move, they're not doing anything. Therefore, I'm thinking that maybe they might not see well.”

11. ...So They Use Their Antennae.

Giant isopods have two sets of antennae that they use to experience the environment around them. “The small antennas are used more for chemical sensing,” Auten says, “and they have large antennas that are used for physical sensing. When you put the food in front of them, you're letting them sense it, physically and chemically.” They might have a sensory receptor that responds to distortion in the water around them.

12. Want to tell males from females? Look for the peenies.

Dee Ann Auten

Female isopods have a brood pouch, or marsupium, located on their undersides, where they hold 20 to 30 eggs (top right). Males have two specialized organs: Small white appendages, called peenies (top left), that carry sperm (fun fact: smaller isopods usually have bigger peenies, according to Auten), and appendices masculinae (bottom), which they use to transfer sperm to the female. “They'll inject that sperm transfer organ anywhere within the female after she molts—because she's softer—and she's able to take on that sperm,” Auten says.

13. They have the largest eggs of all marine invertebrates.

They measure .51 inches in diameter. Females don’t eat when they’re brooding; instead, they bury themselves in sediment to reduce energy use and to protect the eggs.

14. And babies come out looking just like big isopods.

Juvenile giant isopods, or mancae, don’t have a larval stage; they’re approximately 3.4 inches long when they emerge and look exactly like adults. All they’re missing is the last pair of pereopods, or legs; when fully grown, they will have seven pairs of legs total.

15. To Grow, They Shed their Exoskeletons.

Younger isopods molt often to gain size, but “when they get older, they don't molt as much,” Auten says. “They are capable of molting, but they’ve already reached their size, so they’re not going to molt as much—or they’re not going to molt at all, because molting is only for growth.”

16. Isopods bite!

Photo courtesy Flickr user Damien du Toit; cc

“I wear gloves when I work with ours,” Auten says. “They're scavengers—they're definitely going to bite on anything. But it's a small bite, it's nothing big. They don't have big mouths.”

17. They curl up when threatened.

Auten says that isopods can potentially be eaten by anything that’s bigger than them, and when they’re threatened, they curl up into a little ball—just like their land-locked relatives, pillbugs. “If it's eating something and a fish is trying to come over and take the food from them or bite their appendages, they'll roll over to keep their food or to keep their soft organs underneath protected,” Auten says.”They would cover themselves so that nothing will attach to them. Or they'll hide in a crevasse somewhere so that nothing can find them.”

18. There’s a whole album dedicated to songs about them.

It’s called Songs About Giant Isopods, and you can listen to it here.

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Big Questions
Should You Keep Your Pets Indoors During the Solar Eclipse?
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By now, you probably know what you’ll be doing on August 21, when a total solar eclipse makes its way across the continental United States. You’ve had your safety glasses ready since January (and have confirmed that they’ll actually protect your retinas), you’ve picked out the perfect vantage point in your area for the best view, and you’ve memorized Nikon’s tips for how to take pictures of this rare celestial phenomenon. Still, it feels like you’re forgetting something … and it’s probably the thing that's been right under your nose, and sitting on your lap, the whole time: your pets.

Even if you’ve never witnessed a solar eclipse, you undoubtedly know that you’re never supposed to look directly at the sun during one. But what about your four-legged family members? Shouldn’t Fido be fitted with a pair of eclipse glasses before he heads out for his daily walk? Could Princess Kitty be in danger of having her peepers singed if she’s lounging on her favorite windowsill? While, like humans, looking directly at the sun during a solar eclipse does pose the potential of doing harm to a pet’s eyes, it’s unlikely that the thought would even occur to the little ball of fluff.

“It’s no different than any other day,” Angela Speck, co-chair of the AAS National Solar Eclipse Task Force, explained during a NASA briefing in June. “On a normal day, your pets don’t try to look at the sun and therefore don’t damage their eyes, so on this day they’re not going to do it either. It is not a concern, letting them outside. All that’s happened is we’ve blocked out the sun, it’s not more dangerous. So I think that people who have pets want to think about that. I’m not going to worry about my cat.”

Dr. Jessica Vogelsang, a veterinarian, author, and founder of pawcurious, echoed Speck’s statement, but allowed that there’s no such thing as being too cautious. “It’s hard for me to criticize such a well-meaning warning, because there’s really no harm in following the advice to keep pets inside during the eclipse,” Vogelsang told Snopes. “It’s better to be too cautious than not cautious enough. But in the interest of offering a realistic risk assessment, the likelihood of a pet ruining their eyes the same way a human would during an eclipse is much lower—not because the damage would be any less were they to stare at the sun, but because, from a behavior standpoint, dogs and cats just don’t have any interest in doing so. We tend to extrapolate a lot of things from people to pets that just doesn’t bear out, and this is one of them.

“I’ve seen lots of warnings from the astronomy community and the human medical community about the theoretical dangers of pets and eclipses, but I’m not sure if any of them really know animal behavior all that well," Vogelsang continued. "It’s not like there’s a big outcry from the wildlife community to go chase down coyotes and hawks and bears and give them goggles either. While we in the veterinary community absolutely appreciate people being concerned about their pets’ wellbeing, this is a non-issue for us.”

The bigger issue, according to several experts, would be with pets who are already sensitive to Mother Nature. "If you have the sort of pet that's normally sensitive to shifts in the weather, they might be disturbed by just the whole vibe because the temperature will drop and the sky will get dark,” Melanie Monteiro, a pet safety expert and author of The Safe-Dog Handbook: A Complete Guide to Protecting Your Pooch, Indoors and Out, told TODAY.

“If [your pets] have learned some association with it getting darker, they will show that behavior or at a minimum they get confused because the timeframe does not correspond,” Dr. Carlo Siracusa of Penn Vet Hospital told CBS Philly. “You might put the blinds down, but not exactly when the dark is coming but when it is still light.” 

While Monteiro again reasserts that, "Dogs and cats don't normally look up into the sun, so you don't need to get any special eye protection for your pets,” she says that it’s never a bad idea to take some extra precautions. So if you’re headed out to an eclipse viewing party, why not do your pets a favor and leave them at home. They won’t even know what they’re missing.

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Big Questions
Why Can't Dogs Eat Chocolate?
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Even if you don’t have a dog, you probably know that they can’t eat chocolate; it’s one of the most well-known toxic substances for canines (and felines, for that matter). But just what is it about chocolate that is so toxic to dogs? Why can't dogs eat chocolate when we eat it all the time without incident?

It comes down to theobromine, a chemical in chocolate that humans can metabolize easily, but dogs cannot. “They just can’t break it down as fast as humans and so therefore, when they consume it, it can cause illness,” Mike Topper, president of the American Veterinary Medical Association, tells Mental Floss.

The toxic effects of this slow metabolization can range from a mild upset stomach to seizures, heart failure, and even death. If your dog does eat chocolate, they may get thirsty, have diarrhea, and become hyperactive and shaky. If things get really bad, that hyperactivity could turn into seizures, and they could develop an arrhythmia and have a heart attack.

While cats are even more sensitive to theobromine, they’re less likely to eat chocolate in the first place. They’re much more picky eaters, and some research has found that they can’t taste sweetness. Dogs, on the other hand, are much more likely to sit at your feet with those big, mournful eyes begging for a taste of whatever you're eating, including chocolate. (They've also been known to just swipe it off the counter when you’re not looking.)

If your dog gets a hold of your favorite candy bar, it’s best to get them to the vet within two hours. The theobromine is metabolized slowly, “therefore, if we can get it out of the stomach there will be less there to metabolize,” Topper says. Your vet might be able to induce vomiting and give your dog activated charcoal to block the absorption of the theobromine. Intravenous fluids can also help flush it out of your dog’s system before it becomes lethal.

The toxicity varies based on what kind of chocolate it is (milk chocolate has a lower dose of theobromine than dark chocolate, and baking chocolate has an especially concentrated dose), the size of your dog, and whether or not the dog has preexisting health problems, like kidney or heart issues. While any dog is going to get sick, a small, old, or unhealthy dog won't be able to handle the toxic effects as well as a large, young, healthy dog could. “A Great Dane who eats two Hershey’s kisses may not have the same [reaction] that a miniature Chihuahua that eats four Hershey’s kisses has,” Topper explains. The former might only get diarrhea, while the latter probably needs veterinary attention.

Even if you have a big dog, you shouldn’t just play it by ear, though. PetMD has a handy calculator to see just what risk levels your dog faces if he or she eats chocolate, based on the dog’s size and the amount eaten. But if your dog has already ingested chocolate, petMD shouldn’t be your go-to source. Call your vet's office, where they are already familiar with your dog’s size, age, and condition. They can give you the best advice on how toxic the dose might be and how urgent the situation is.

So if your dog eats chocolate, you’re better off paying a few hundred dollars at the vet to make your dog puke than waiting until it’s too late.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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