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Humans aren't the animal kingdom's only engineers.
Odds are you've heard about beavers, whose famous dams can be hundreds of meters long.
But while beavers steal the spotlight, there are plenty of other animals quietly building some impressive stuff!
A while ago, we talked about some of the coolest things built by bugs.
And here are five more amazing feats of engineering by all types of animals, from optical illusions to entire cities underground.
Sociable weaver birds don't build little nests between a couple of branches like your average bird does.
At about 14 centimeters long, these birds are pretty small.
But they build the largest tree nests in the world: up to six meters tall and three meters wide, able to house up to a hundred families at once.
And just like human engineers would, they start with the foundation.
The nests can weigh a few tons, so they need to be supported by very thick branches.
After that, they gather progressively smaller branches and twigs to fill out the rest of the structure before finally moving on to thin grasses for the nest's very outer layers.
Each family makes its own apartment that they're constantly improving, changing, and adding to--because, you know, sometimes the stuff on your walls starts to feel stale.
Although your walls probably don't have spiky straws to keep out snakes.
If they do, you might want to move.
The nests don't just protect sociable weavers from predators; they also protect the birds from the intense temperatures of the southern African Kalahari Desert.
Summer days can reach 43 degrees Celsius, but the nests block a lot of that heat, keeping the birds inside cooler and letting them conserve water that most birds would have used to cool themselves down.
Winter nights, on the other hand, can drop down to -10 degrees.
And on those cold nights, the nests can be 30 degrees warmer than the outside air—again, letting the birds conserve energy they would otherwise have had to use to stay warm.
With such nifty homes, it's no surprise that weaver birds live in their nests year-round.
They even pass the nests down generations, with some nests lasting a century or more.
Others aren't so lucky.
In the rainy season, the already heavy nests can get so waterlogged that they bring down the tree they were built in.
But when that happens, weaver birds just get right back to engineering.
To us, male great bowerbird projects might not look as impressive as weaver bird nests, but that's only because we're looking from the wrong angle.
The birds don't just build something beautiful.
They use a trick of psychology and optics to make it—and themselves—look even better.
All sorts of bowerbird species make elaborately colorful stages or caves, called "bowers", by collecting things from the world around them.
If a female is impressed by a male's bower, the male does a dance to try and woo her even further.
Compared to other bowerbirds, though, the great bowerbird's bower can look a bit… dour.
Sure, there are a bunch of rocks surrounded by loops of sticks where the male dances, but it's not usually the colorful arrangement you find with other bowerbirds.
Scientists only discovered the secrets of these bowers a few years ago, when they realized that the birds tended to put bigger stones toward the back and smaller ones toward the front.
When the male stands near the bigger stones, it creates what photographers and architects know as forced perspective.
They use it all the time to trick your brain into thinking something's a different distance from you than it actually is—
like when your friend returns from a trip to Pisa with a picture that makes it look like they're holding up the Leaning Tower, even though they're a few hundred meters away.
With the bowerbirds, having small stones near the front means that to the female, everything in the bower looks closer than it actually is—and therefore the male, towering over it all, is much bigger than he actually is.
So by cleverly engineering his bower, the male great bowerbird is able to get all the ladies.
Or, at least, the ladies who like what he's built.
To find our next engineers, you need to go where few birds ever venture: the bottom of the sea.
That's where you'll find the 12-centimeter male pufferfish, and their underwater sand circles.
It took scientists sixteen years to figure out where those two-meter circles came from after first noticing them off the coast of Japan in 1995.
And when they did finally see the fish in action in 2011, it seemed to be a previously unknown species.
The details are still a little murky, but we know males make the circles to impress females.
They make the long, wavy grooves by flapping their fins along the surface of the sand.
And since that's still not enough to impress a potential mate, they decorate their circles with shells to liven things up.
Then, as a cherry on top, they go out and find fine, pretty-looking sand to spread around the circle, especially in the center.
Females pick a circle they like the best and lay their eggs there, but no one's sure what exactly makes them choose one circle over another.
The clever engineering here is in fluid dynamics, which the pufferfish use to avoid having to gather all that pretty center sand themselves.
The wiggly grooves around the outside of the circle slow water down as it moves toward the center, where it tends to drop fine sand in those cool wavy patterns.
Even after all the effort that goes into building the circles, they still don't last very long.
Ocean currents tend to destroy them after a couple of weeks, meaning that male pufferfish have to build a new one every year.
But on the plus side, that means every year they get to show off their fluid dynamics skills.
We humans have only been using electricity to our advantage for a couple of centuries.
But at least one species of hornet has used electricity to keep their babies comfortable for far longer than that.
Oriental hornets lay their eggs in a nest, and the larvae who hatch from those eggs spin silk cocoons around themselves so they can keep developing.
The baby hornets end up deformed if their cocoons get too hot or too cold during development, so the grown-ups have a number of creative ways to keep their nests and those critical cocoons at the right temperature.
When things heat up, they fan the cocoons with their wings or spray them with water droplets.
And when it gets too cold, they blow warm air stored in air sacs on their bodies to keep the cocoons warm.
But adults aren't always needed to keep cocoons safe, because the nests are built to insulate them from the outside world, and they're also really wet on the inside.
Water can absorb a lot of energy without changing its temperature much, so all that water in the nest keeps the inside temperature nice and level.
So even without adults around, the inside of a nest can take a few days to reach the same temperature as the air outside.
But the hornets have one final trick up their exoskeleton: the silk around their cocoons is thermoelectric.
Changing the temperature of a thermoelectric material makes electric current flow through it.
When a nest starts getting too warm, a tiny current starts flowing from one end of the cocoon to the other, building up electric charge on one end of it.
Since energy from the outside air is being used to drive the current, it gets used up before it can heat the cocoon—and the hornet inside stays cool.
Then, when the temperature gets too low, the process reverses and charges flow back to where they came from originally.
Since it took heat to move them, they release heat as they move back, and the current heats up the cocoon to a more comfortable temperature again.
In the early 1900s, scientists found a prairie dog town in Texas.
It was a bunch of interconnected underground tunnels, just like other prairie dog communities throughout the western United States at the time.
But this one was enormous— the biggest anyone's ever seen.
It covered about 64,000 square kilometers, and was home to an estimated 400 million prairie dogs!
Which is a lot of little rodents running around underground.
Today's prairie dogs have been kicked out of most of their historical habitat, but they still employ the same engineering smarts they used to create that gigantic colony in Texas.
The simplest prairie dog homes are tubes that go from an entrance at ground level down to a room that's a meter or two underground.
But their burrows are typically much more complicated.
For one thing, they tend to have multiple entrances.
Between entrances, there's a big U-shaped hallway, with the bottom of the U sitting a few meters underground.
And off that main hallway are a whole bunch of individual chambers for families to raise their pups.
The most obvious reason to build multiple entrances is that if a predator comes in the front door, everyone can run out the back.
But there's another reason, too:
Having tunnels be so long and deep also means that it's hard for oxygen from above ground to get all the way in and replace what's used up when the prairie dogs breathe.
To solve that problem, prairie dogs build one entrance upwind and another downwind.
Wind flowing past the upwind entrance pushes air all the way through the tunnels and out the downwind exit, bringing fresh oxygen throughout the tunnel system even in a light breeze.
Huge prairie dog towns might have kilometers of tunnels with tons of different entrances and ventilation tubes all over the place to keep air flowing through all the time.
It's just one more way other animals have been using technology to engineer our world for far longer than humans have, from birds to fish to hornets.
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