Sea pigs that squiggle and hagfish with no eyes, those naked mole rats and larvae from botflies, cranky rock crabs that crush my nerve endings, these are a few of my LEAST favorite things. Not the dog bites, not the bee stings, those bitches. OK, I hate those things mostly cause they intolerably ugly or intolerably UUUGH (botflies I’m looking right at you and don’t even pretend I’m not), call me petty, whatever. These things don’t scare me, though. They’re not dangerous, why would they? Venomous snakes and spiders are kind of scary, but venom is a hassle for them to produce so they try to warn you when you’re too close and making them nervous (see: rattlesnakes, spitting cobras, etc). Hell, brown recluse spiders and black widows will run before anything else. Large predators, sure, but pack some bear spray, travel in groups and I should be good to go. Sharks? Pssht, I barely sea kayak and have no interest in surfing so no shark is going to mistake me for a turtle snack anytime soon. You want to know what’s really scary? What would make me don a custom head-to-toe wetsuit if I went swimming in Australia? Box jellyfish. Goddamn box jellies. I can hear you Hawaiians out there (assuming I have Hawaiian readers…), “Man, what’s the deal? You get stung by a jelly, you get over it. Spray some ammonia on it and get back in the water.” I call bullshit, Hawaii. Box jellies are serious business. So what if it’s not a true jellyfish (scyphozoa) and belong to its own class (cubozoa). Even your Irukanji box jelly (Carukia barnesi) venom can cause difficulty in breathing, vomiting, coughing and also possibly death. Not to mention the excruciating pain, at the sting site, as well as the stomach, limbs, back and head. Put ammonia on THAT, Hawaii.
So why is a dumb jelly scarier than a snake that can spit venom at my eyes or a large cat that could rip my throat out with only a “playful’ swipe? You can prepare for that shit. Walk away from snakes you don’t know (and say “no” if they offer you drugs) and if you think any big mammal is a danger, CARRY BEAR SPRAY. As a side note, I’ve been stalked by a tiger while working at a zoo. At least the tigers there thought that if they weren’t moving, you couldn’t see them. So I’d be walking to lunch past the back of the tiger exhibit and hear a sound, turn, and see a tiger frozen mid-step. Turn away, turn back, tiger had moved one more step. Maybe had tried hiding behind a rock the size of his head (but not the rest of his 350lb+ bulk). Not that Mushi would necessarily behave like that in the wild, BUT IT’S FUNNY. Also, bear spray does wonders. ANYWAY, that “dumb” jellyfish has eyes. Four small structures simply respond to light and accompany two real eyes; structures complete with lenses, corneas and retinas. It can see, process sights and hunt based on that. You may not look like dinner, but that “dumb” jelly does not care enough to avoid you. DOES NOT CARE. It can kill you just because it can’t be bothered to try and avoid you. This is a predator skilled enough to find its prey and deadly enough not to worry about predators of its own. It can also kill you when it’s dead. How about THAT, Hawaii?
ADDENDUM:Almost forgot to explain the box jellies mode of envenomation. Remember the nematocysts? Of course you do, I talked about them in Nudi Time ( https://dailyscienceblog.wordpress.com/2013/01/21/nudi-time/ ). Basically those are cells that hold contact-activated barbs on threads. It’s like a land mine, but instead of an explosion when you touch it, a poisoned grappling hook shoots out. Explosion of HORRENDOUS PAIN. Also the barbs regenerate after use. In most jellies the cells stop working after death, but box jellies are determinedly mean bastards so their nematocysts can still fire after they die. Happy swimming!
Source
Laidler, Keith. 2009. Animals: A Visual Guide to the Animal Kingdom. Quercus Publishing Plc, London.
Daily Science (blog) 