April 27 is Save the Frogs Day, and to celebrate, we've put together a Halloween-worthy lineup of some of the freakiest and most fascinating amphibians around. You can expect a display of jaws, claws, toxins and other bizarre amphibian adaptations. 

Javan rhino portrait

Wood frog (Lithobates sylvaticus

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Dave Huth, Flickr

When it comes to hunkering down for the winter, the wood frog Rana sylvatica doesn’t take any half measures … it literally turns itself into a solid little frogsicle. The heart stops, all muscle and breathing movements cease and up to 70% of the body freezes (even the brain and the lens of the eye). And yet come spring, the frogs thaw out and hop right back into life. This amazing case of cryogenics is possible thanks to several special adaptations, including the 'antifreeze' role played by glucose in the frog’s body. Check out the frog in all of its frozen glory here.

Water-lily reed frog (Hyperolius pusillus)

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Image: Martin Grimm, Flickr

The Fantastic Four have 'Invisible Woman' … amphibians have Hyperolius pusillus. Water-lily reed frogs might be common, but their incredibly well-adapted camouflage is anything but ordinary. Light green in colour and no bigger than a dime, these amphibians can be pretty tricky to locate. However, it's their translucent skin that really makes this species unique. Shine a light at their bellies and you can see everything from blood vessels and intestines to their miniature beating hearts. Even their skeleton is visible (and in some species the bones are green to help conceal them in the undergrowth!). Thanks to some extremely thin skin on their stomachs and extremities, and a severe lack of pigment in their cells, their bodies do not reflect the incoming light but rather allow it to pass straight through them.

Hairy frog (Trichobatrachus robustus)

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Amphibian horror story, anyone? Meet Trichobatrachus robustus – also known in herpetological circles as the frog that responds to threats by breaking its own bones, which thrust their way through its toe pads Wolverine-style, to be brandished like a set of extendable claws. And as if that wasn't enough of a party trick, males of the species also put on a hairy display come breeding season, sprouting hair-like strands made of arteries and skin to boost their oxygen intake to help them meet the demands of parenthood. 

Gliding tree frog (Agalychnis spurrelli)

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Image: layzell2011, Flickr

If the name hasn't given it away already, the gliding tree frog's most notable feat is its ability to fly … well, kind of. Agalychnis spurrelli lives almost exclusively in the treetops of dense tropical jungles, hundreds of feet above the forest floor. But living the high life is not without its dangers. Formidable predators such as the tree boa pose a serious threat to the sure-footed tree frogs. Luckily for these amphibians, they can use the extensive webbing on their feet and hands like a parachute to escape by gliding to the forest floor. Okay, it's not so much flying. It's more falling with style. But they are able to steer themselves pretty comfortably through the air, sometimes landing as far as 50 feet away.

Sharp-nosed grass frog (Ptychadena oxyrhynchus)

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Image: Bernard DUPONT, Flickr

It might not look like a record holder, but don't let the unimpressive size of Ptychadena oxyrhynchus fool you … these frogs are pretty phenomenal jumpers. It was a little sharp-nosed grass frog called 'Santjie' that thrust the species into the global spotlight, when she jumped her way into the Guinness Book of Records with a 10.3 metre leap in 1977. It was and remains today the farthest frog jump ever recorded. That'll do, Santjie … that'll do.

Southern Darwin frog (Rhinoderma darwinii)

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Image: Flavio Camus, Flickr

Its tiny stature and Pinocchio-impersonating skills aside, the Darwin frog makes this list thanks to its unusual version of daddy daycare. Daddy duty begins as soon as the newly emerged tadpoles begin to wriggle. To keep the young'uns safe, the male deposits the entire brood inside his vocal sac, which extends from throat to groin. Thus ensconced, the progeny will happily grow, even displacing dad's internal organs to make more room. But the time eventually comes for the youngsters to fend on their own (about 50 days later) – at which point they're unceremoniously vomited up in a secluded spot and sent on their way. 

African clawed frog (Xenopus laevis)

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Image: Brian Gratwicke, Flickr

Their fascinating history as medical test subjects aside, there's plenty of anatomical quirkiness to the African clawed frog – like the missing tongue and the presence of lateral lines to sense vibrations in the water when they're hunting. And then there's that voracious appetite for just about anything, alive or dead, the frogs can shovel down their throats (it goes something like this). On a more serious note, the species is also considered a highly destructive pest and has been implicated in spreading the deadly amphibian chytrid fungus around the world. 

Grey foam nest tree frog (Chiromantis xerampelina)

The foam nest frog bags the medal for inventive nesting material: bubbles! For Chiromantis xerampelina, baby-making is basically one crazy foam party. When the time comes to go forth and multiply, the division of labour is simple: females lay eggs and produce the foam while males do the “foam frothing” with their back legs. It might look like a whole lot of gelatinous goo, but there's nothing flimsy about a foam nest: the end product can withstand what the weather might throw at it and helps to prevent the frog progeny from drying out.  

Poison dart frog (Dendrobates auratus)

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Image: Brian Gratwicke, Flickr

Pretty. Beguiling. Lethal. We all know poison dart frogs have a deadly reputation, and among them you will indeed find some of the most toxic creatures on earth. Though we know of more than a hundred different species, new ones are still being discovered ... and with them new possibilities for deriving potent drugs from their potent poisons. Sadly, many poison dart frogs are now under threat as we continue to decimate their habitats. 

African bull frog (Pyxicephalus adspersus)

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Image: Ian White, Flickr

Meet the heavyweight champion of the southern African frog world. A fully grown adult male can weigh in at a staggering one kilogram (put your two hands together side by side and you'll get an idea of just how big that is). As adults, African bullfrogs forage and feed in open grasslands, devouring pretty much anything that moves and will fit inside their jaws: rodents, snakes, birds (yes, birds!), lizards, other frogs ... the list goes on. (Scary fact: the width of their mouths allows them to swallow mice whole.) They're armed with two bony projections (odontoids) that look like teeth on the lower jaw, which are used for gripping prey and self-defence during territorial disputes. And bullfrog sex? Bullfrog sex is just plain terrifying. 

Check out Crazy Monster Frogs on the Smithsonian Channel for more.

Top header image: Keith Kissel, Flickr