Human babies are helpless little things that depend on a lot of care for a very long time. But we humans aren't the only ones who can't make it on our own. Some animal babies, mostly birds, but some mammals too, are usually cared for by two parents. Others rely only on the care of their mothers. But probably the rarest form of parental care among other animals comes in the form of the single dad. 

Take the giant water bug, for example. In general, parental care of any kind is pretty rare among insects, but paternal care is nearly unheard of, with only thirteen known exceptions. Found in freshwater ponds throughout the northern United States and Canada, giant water bugs can be up to 10 centimeters long, and are sometimes charmingly referred to as "toe biters." And it's pretty easy to pick a giant water bug dad out of the crowd, because he is the one covered in eggs. 

See, once they mate, the female deposits and glues 100 or more eggs on the male's back before peacing out. And even though it makes it harder for him to hunt for prey and easier to get caught as prey, he will schlep those eggs around until they hatch. He'll also comb his legs through them to keep them clean and free of fungal infection, and make sure to air them out at the water's surface. 

Now, piggy-backing your offspring is one thing but imagine carrying a bunch of squirmy babies around in your mouth. That's basically what South American Darwin's frog fathers do. The female deposits her eggs on the ground in moist leaf-litter, where the male fertilizes them. Then, she hops off, never to be seen again, and the male keeps watch over the eggs for the next three weeks. Once the growing larvae start wiggling around inside their eggs, he swallows them; not as a snack, but to hold them in his pouch-like vocal sac.

A few day later, the eggs hatch into tadpoles, but they stay inside the papa frog's pouch for 50 to 70 more days as they gradually develop into something more frog-shaped. Once they're fully transformed the froglets leave the vocal sac and then just hop out into the world through their dad's mouth. 

But when it comes to paternal care that really goes above and beyond, one group of dads really takes the prize. They don't just sit on their eggs, or carry them on their backs, or in their mouths; they actually get pregnant and give birth. Sort of. I'm talking about seahorses. As seahorses mating pairs get frisky, the female  deposits her eggs into a special pouch on the male's stomach, called the brood pouch, as the male releases sperm to fertilize them.

Then, the male carries the eggs for the 10 to 25 day gestation period, depending on the species, providing nutrients and oxygen, as well as helping the embryos balance their fluids and salts. Once the babies are fully-developed, the male experiences abdominal contractions that help shoot the teeny-tiny seahorses out of the pouch and into the ocean. 

Now, the animals we're talked about so far put a lot of time and energy into taking care of their developing young. But once the water bugs, or frogs, or seahorses emerge, the dad's involvement is over, and they go off into the world on their own. Emus do things a little differently. These large, flightless Australian birds are often polyandrous, meaning they'll court and mate with multiple partners. Once a female lays a clutch of up to 24 eggs, her work is done and she's free to cruise for other males or do whatever else she wants.

Meanwhile, her mate's job is just beginning, and he's literally not going anywhere. During the 7 to 8 week incubation period males don't eat, drink, or pee or poop. Instead, they carefully tend their eggs, padding the nest with dried grasses and gently rotating the eggs every few hours to make sure each one gets enough heat. Once they hatch, chicks stay with their fathers for nearly seven months, as he teaches them how to forage for food while aggressively chasing off anyone who gets too close, including their mother. 

For all of these animal dads, caring for offspring can take up a lot of resources. But in the process, they're helping increase their young's chance of survival. Plus, they get to show any females in the area that they make good parents, increasing their chances of pumping more of their genes into the world during the next breeding season. So all that investment, in the end, is worth it. 

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