An adult Emperor Penguin with its chick at Cape Crozier, Antarctica. (istockphoto)

When you think about toughness, you probably consider how strong something is. But there is another kind of toughness you might not have considered. How well does a species deal with its surroundings? Humans, for example, are pretty helpless. A naked human can endure only a narrow range of environments. Too hot? We’re dead. Too cold? We’re dead. Not enough water? We’re dead. Too much water? Same thing.

But a number of animals on Earth can survive a dizzying array of environments. Here are a few of them.

Emperor penguin. This flightless bird lives in the Antarctic, where winter temperatures can dip way below zero. Surprisingly, the birds breed in the winter. After the female lays an egg, the male incubates the egg (keeps it warm) by balancing it on his feet. He is able to do that for two reasons. First, a pouch of skin covered with an inch-thick coat of feathers does an amazing job of insulating the egg from the cold, blustery air. Second, he doesn’t mind standing around for 65 days until the chick hatches. What a dad!

You want to see tough? Well, you’re going to need an electron microsope, because the tardigrade is not much bigger than a grain of salt. (Bob Goldstein and Vicki Madden/Associated Press)

Wood frog. Most animals that hibernate live off their fat stores and have thickened coats of fur to protect them from the cold. One species of wood frog that lives in Alaska and Canada has figured out another way to survive the cold: It freezes!

When most animals are exposed to sub-zero temperatures for more than a short period of time, the water in their blood and tissues freezes. When that happens, water is pulled from within the animal’s cells. The cells then become dehydrated and die. That does not happen to wood frogs because the animal has adapted a system that keeps water in the cells if the frog’s tissues freeze. As a result, the animals can freeze and thaw many times every winter with no ill effects. Frogsicles, anyone?

Giant tube worm. Growing up to six feet long, the giant tube worm lives on the pitch-black floor of the Pacific Ocean a mile or more below the surface. It is found near cracks in the ocean floor that release hot water into the surrounding area. The water contains chemicals such as hydrogen sulfide that are toxic to most animal life. (Hydrogen sulfide is what gives rotten eggs their stinky smell.)

The giant tube worm does not have a mouth or stomach, so it does not eat in the usual sense. Instead, it has developed a symbiotic relationship with bacteria that live inside its body. (That means the worm and bacteria help and depend on each other.) The tube worm filters hydrogen sulfide from the water, and the bacteria break down the chemical, which releases nutrients the tube worm uses to nourish itself.

Tardigrade. This tiny creature gets first prize for being the toughest animal on Earth. Tardigrades average half a millimeter in length (a little longer than a grain of salt). They are found all over the world but thrive best in a moist environment. Tardigrades have four pairs of legs with claws on the end. They have a mouth with daggerlike teeth that are used to feed on algae, plant cells and animals. If a tardigrade were a big as a horse, it would look like a creature from a horror movie!

Tardigrades can survive boiling water, extreme cold, radiation, the vacuum of space and pressures six times greater than what’s found in the deepest ocean. They can even last 10 years or more without food or water. Keep that in mind the next time you get thirsty on your way back from soccer practice.

— Howard J. Bennett

A special thanks to Alissa Simon, who taught the author about the existence of tardigrades.