Unlike human infants, who are virtually helpless after birth (and well beyond), animal babies tend to arrive well-equipped for survival right off the bat. It's Mother Nature's way of ensuring they have a fighting chance against predators, absent parents and punishing surroundings.

For a select few, though, their earliest moments are especially grueling. These unlucky infants not only face harsher trials from the get-go, they also must go to jaw-dropping lengths to endure. Here are several of the animal kingdom's ultimate infant survivors.

Barnacle geese

To avoid predators like Arctic foxes, barnacle geese lay their eggs high on sheer mountain cliffs. These scrappy risk takers aren't much for pampering their young either. Instead of bringing their newborn goslings food from the ground, the parents expect their hatchlings to get their own. How? By taking the ultimate plunge. That's right, when goslings are only a few days old and can't yet fly, they embark on a death-defying leap to their waiting parents below, sometimes plummeting 400 feet (akin to falling 36 stories). As you can imagine, only the fittest (fluffiest, lightest and most parachute-like) survive.

Braconid wasps

Several species of parasitoid wasps inject their eggs into living caterpillars, which serve as involuntary surrogate wombs. Offspring of the wasp species Cotesia glamerata (featured in the video above) participate in a particularly gruesome birth ritual to ensure their survival. Once larvae hatch inside the caterpillar, they begin eating its interior, careful to avoid key organs needed to keep it alive. In preparation for their pupa stage, these determined babies literally chew through the caterpillar's skin, releasing chemicals that zombify it as they emerge. Next, they spin a protective cocoon to begin their transformation from larva to wasp. But that's not the end of their bizarre delivery experience. During this time, the larvae themselves are vulnerable to being injected with eggs from other parasitic wasp species. Remarkably, the beleaguered, brainwashed caterpillar is induced to spin a silken cocoon blanket that covers the wasp cocoons instead of spinning its own cocoon to become a butterfly. It then vigilantly guards the developing babies until finally starving to death.

Marine iguanas

After laying their eggs in protective holes in the sandy beaches of the Galapagos Islands, marine iguana moms take off for good. Once hatched, the parentless babies instinctively sprint across the sand for cover in nearby rocks until they're big enough to safely swim in the ocean. Unfortunately, during their mad dash, hatchlings become easy pickings for hungry predators, including swarms of slithering racer snakes (dramatically documented above).

Crocodiles

Like marine iguanas, mama crocodiles bury their eggs in deep holes away from predators. But unlike them, these moms stick around to watch over their underground incubators. It sounds like cushy start to life, but crocodile babies face some potential challenges. One is the chance of suffocation. When they're ready to hatch, unborn crocs begin making loud chirping sounds from inside their deeply buried eggs. This prompts Mom to immediately dig them out so they can breathe as they emerge from their shells. The next part may be visually alarming, but it bolsters the hatchlings' chances of survival. Mom scoops them up into her giant bone-crunching, snaggletooth jaws (up to 15 at once) and carries them to the water where she'll continue nurturing them for several more months.

Giraffes

Newborn giraffes receive a rather jarring welcome to the world. After emerging from their standing mother's womb, each calf drops nearly six feet to the ground. Considering they arrive weighing a whopping 150 pounds, that's one big thud. But not to worry. The hard landing serves a vital function by rupturing the amniotic sac, severing the umbilical cord and initiating breathing. But that's not the only extreme that just-born calves face. With predators at every turn, they need to literally hit the ground running. Thirty minutes after tumbling from the birth canal, newborns can stand and only hours later they are galloping across the savanna.

Sand tiger sharks

You've heard of sibling rivalry, but baby sand tiger sharks take it to a deadly extreme. They devour their unwitting brothers and sisters while still in the womb (a nightmarish practice called intrauterine cannibalism). Here's how it plays out. Mother sand tiger sharks carry several fertilized eggs in each of their two uteruses, but they only give birth to two live pups at a time. That's because the first embryo to hatch in each uterus gets a head start on growth. These firstborns maintain dominance in utero — and fuel their own growth in preparation for birth — by gobbling up their straggling siblings in a fratricidal feeding frenzy.

Opossums

Shortly after birth, opossum newborns — hairless, sightless and no bigger than a dime — begin the arduous trek across their mother's body to her pouch where they grab a teat and hang on for the next two months. Eventually, they and their littermates (as many as 13) grow too big for comfort, but they're not yet savvy enough to wander on their own. The solution? For a few more weeks, they perch precariously on Mom's crowded back, clinging for dear life as she goes about her daily business.

Spiders

The sacrifices moms make for their kids is undeniable. But some spiders take maternal sacrifice to a whole new level. These supermoms make the ultimate sacrifice: They allow their offspring to eat them alive. Several spider species engage in mother-eating (matriphagy). In the video above, spiderlings devour sacs of unfertilized eggs specially laid by their mom, but that doesn't quell their hunger for long. Luckily, Mom has one more culinary trick up her sleeve. She vibrates the web and her spiderlings swarm around her, sinking in their tiny venomous fangs. Ghastly doesn't begin to describe it, but the venom slowly dissolves her from the inside out, providing nourishment for her spiderlings until they can fend for themselves.

8 extreme animal newborns
From sibling cannibalism to daring cliff dives, some animal babies face unimaginable survival tests.