Dread them.

Run from them.

[hitting wood] But that won’t stop these unwelcome house guests from coming to visit you anyway.

In fact, you’ve probably got them in your home right now making themselves comfortable.

Let’s start with the tiny dust mite.

It might seem harmless, but in large numbers they can cause serious problems.

Long ago – around the time we started  growing our own food – humans settled down.

We went home, inside.

We built permanent shelters to protect us from the elements ... and keep the wild animals at bay.

Or so we thought.

Surprise!

The animals were right there with us.

They still are.

This is dust.

Zoom in and you find an ecosystem almost as elaborate as the one we left outside.

But small enough for us to forget it exists.

Dust is pretty much anything small.

But the most important ingredient of dust – at least for the purposes of this story – is skin.

Your skin.

Her skin.

His skin.

Tiny flakes that fall off our bodies all day long.

Researchers at the California Academy of  Sciences in San Francisco collect and study house dust to find out  what exactly makes up this micro-universe.

[vacuuming] Even the cleanest homes are teeming with tiny, almost invisible roommates.

And even more so if you have pets or kids or live on the ground floor.

Most homes have over 100 species … no matter how often you vacuum.

Not just these guys.

But these.

And these.

And these.

Most of these microscopic roommates are harmless.

Just freeloaders, basically.

But one can cause real trouble.

The house dust mite.

This is like the roommate who leaves  his crap around and makes you sick.

Dust mites don’t bite people.

They don’t need to.

We feed them constantly.

Skin flakes are hard to digest.

It’s like eating hair ... or feathers.

So dust mites have powerful digestive enzymes to break the skin down.

Those enzymes turn up in dust mite poop.

And let’s just say you really don’t want to know how much dust mite poop is in your house.

When people breathe dust, they breathe in the poop  – and the enzymes, too ... which irritate the lungs and can aggravate asthma, especially in kids.

Like us humans, dust mites haven’t always lived inside either.

These tiny relatives of spiders and scorpions once lived in birds’ nests.

But then, some intrepid dust mites made the jump ... from birds’ homes to ours.. And as our society thrived and grew, so did theirs.

These bed bugs are after your blood and they go for it while you’re sleeping.

Keep watching to see how researchers  stop them dead in their tracks.

Good night, sleep tight, don’t let the … OK, you know where this is going.

[ominous music] Lured in by our breath, bed bugs come for us when we’re most vulnerable.

In dreamland, we’re oblivious ... ... to bed bug chow time.

You won’t even feel it.

It’s a quick meal.

Just a few minutes.

But it’s a filling one.

Stuffed with blood, it scurries to a nearby cranny.

The seam of your mattress ... ... or behind a baseboard.

There, they get to work growing their families.

Until you get … [ominous music] You can recognize them by their signature work of art.

These tiny splotches.

It’s the digested blood they leave behind.

In the 1950s, we made bed bugs retreat with DDT.

But some became resistant and now they’re back.

We help them spread – in our clothes  or luggage – when we travel around.

You can kill them with other insecticides or heat,  but their game of hide-and-seek makes it tricky.

Turns out, there might be another way to stop them in their tracks.

Watch this.

It’s just taking a stroll and ... Gotcha!

Its foot is stuck.

This bean leaf can incapacitate the bloodsuckers.

People in the Balkans discovered that years ago   and would spread the leaves around their beds as a trap.

The leaf’s surface is covered in these  tiny hooked hairs called trichomes.

They pierce right through the bed bug’s feet, impaling their soft joints.

Many bean plants – like kidney and green beans – developed the hooks to defend against aphids  and other plant-eating pests.

But it just so happens to work on our bloodthirsty pest too.

Biologist and engineer Catherine Loudon is trying to copy the plant at the University of California, Irvine.

She’s creating a synthetic material that can pierce bed bug feet just like bean leaves do.

It’s not quite as effective as a real bean leaf, but she’s working on it.

In the meantime, bed bugs are still a step ahead.

So keep an eye out.

Spot them early and maybe you can get them before they get you.

Termites can infiltrate your home without being seen, and the results can be catastrophic.

But these tiny homewreckers  wouldn’t be able to do so much damage without the help of special microorganisms hidden in their gut.

That lump on the side of this tree in the Amazon?

It's packed with termites.

In the rainforest, that's a good thing.

They break down wood into stuff other creatures can eat.

But inside our homes, termites are pests.

They cost us billions of dollars of damage every year.

Take these dampwood termites that live on the cool California coast.

They eat wood that’s wet or decayed,  maybe from a leak in your house.

Slowly, but surely, they gnaw and scrape away.

What comes out the other end isn’t waste.

It serves as a kind of mortar.

And dried poop pellets make perfect building blocks for their nests.

In other words, they’re turning  your house into theirs.

What’s amazing is that they can digest wood,  which is so hard, and get nutrients out of it.

We certainly can’t do that.

Termites are one of the only animals that can.

It turns out they don’t do this alone.

Researchers are looking inside termites to figure out who’s actually responsible for this feat.

At the Exploratorium, in San Francisco,   museum biologists give the insect  a little puff of carbon dioxide.

When it’s nice and relaxed, the termite poops itself.

Under the microscope, multitudes appear.

Hundreds of species of microbes  live packed inside a termite’s gut,   about one one-thousandth of a teaspoon.

This big one is called Trichonympha.

It’s not an animal, plant or fungus.

It’s a protist.

Watch it move with the help of its flagella.

Protists like Trichonympha are essential for termites to turn the wood into a source of energy.

They do this by fermenting the wood, much the same way a brewer turns grain into beer.

Something else is hidden deep in the termite’s gut.

A powerful bacterium that combines nitrogen from the air and calories from the wood to make protein.

That’s like turning a potato into a steak.

Termites can’t live without their microbes.

And many of these microbes  can’t live outside the termite.

So what if we used the microbes against their hosts?

Right now, when we want to get rid of termites, we fumigate our houses with poison.

But maybe we could just kill the protists instead.

Louisiana State University entomologists are engineering a gut bacterium to kill gut protists.

They’d sneak the bacteria into the termite colony on something the termites would eat.

The bacteria would kill the protists  that help the termites digest wood,   leaving them surrounded by food but starving.

These cuties are experts in making their way into your house through some secret and slimy passageways.

Check it out.

Ever wonder where those little insects crawling around your bathroom came from?

Bad news: your drain.

With all that fluffy hair, it looks like a tiny moth.

And some do call it a moth fly.

But a fly it is.

A drain fly.

It’s called Clogmia – how appropriate.

It grew up over several weeks, out of sight,  among things you thought you’d washed away.

Drain flies sneak in from the outside,  through a crack in an old pipe, for example,   to sip some water they sensed with this long mustache – their maxillary palps.

And here, on the plentiful gunk in your pipes, they’ll grow a family.

Welcome, little one!

The larva is the length of an eyelash.

That gunk it lives in?

Those are bits of you: hair, saliva and food.

They make a nice meal for bacteria and fungi,   which form this dark, living slime called a biofilm.

This is what the larvae feed on.

It also keeps them well moisturized.

If the larva ends up submerged,  it can still chow down.

It sweeps slime particles out of the water with a hairy mouthpart called the labrum.

And rakes them in with its mandibles.

Underwater, it breathes with a bubble on its backside that it collected at the surface.

This allows it to venture  through deep pools in your pipes.

When larvae, or the more grown-up pupae,   like this guy here, end up in a  toilet bowl, it can be a shock.

You might think the squigglers came out of you!

Ew!

Don’t worry – they can’t live inside us.

And even though the drain flies in your bathroom muck around in bacteria,   they don’t really spread it to humans.

They’re not interested in landing on us.

Or even leaving the bathroom.

They’re in their happy place.

When you wash your hands?

They protect themselves from the water with their hairy wings.

Each hair has ridges that trap air so the drops roll right off.

And if they’re caught off-guard by a sudden surge, the flies skate across.

But they’re not invincible.

When they get trapped underwater long enough, they can drown.

If you find you really need to get rid of them,   drain cleaner helps, but it won’t keep them away forever.

There will always be some slime left behind, deep in your pipes, that could attract the flies again.

So, if they want it, why not let ‘em have it?

Are cockroaches – those disgusting disease-spreading roommates – good for anything at all?

[hitting wood] [hitting floor] Scientists think their super-strength might teach us some tricks that could someday save lives.

The American cockroach is one of the fastest insects on the planet.

It can run up to 3.4 miles per hour.

That’d be like a human knocking out eight marathons over their lunch break.

It uses hooks, called tarsal claws, to flip over ledges.

[cymbal ta-da] [cymbal ta-da] And not even a wall can stop it.

Better to keep up the momentum  and figure it out as you go.

The roach is both tough and flexible.

Its exoskeleton isn’t one large piece of armor,   but many shield-like plates made of a tough material called chitin.

They’re held together by lots of pliable joints.

And they use all those bendy joints to fold up,   origami-style, and push through  impossibly small cracks … … like that gap you never knew existed in your kitchen cupboard.

The cockroach can army-crawl through a space  a quarter of its normal standing height.

That's one reason it's so good at surviving your thwack.

So how much pressure can the cockroach take?

Scientists at UC Berkeley found it can withstand a thwack ... ... equivalent to 900 times its body weight … … and walk away unscathed.

Why are researchers so interested in all this?

They think the roach, despite its ability to make us sick, can teach us to save lives.

One of those researchers is now building robots the size of insects  to squeeze into places you and I cannot.

Like piles of rubble left by major earthquakes or hurricanes.

And maybe down the line, much smaller versions of these robots  could even enter our bodies to perform life-saving tasks!

On the one hand, we want to keep these creatures out ... by sealing cracks, caulking windows  and storing food in airtight containers.

But we also want to learn from them.

The cockroach teaches us that the key to overcoming adversity   isn't just toughness.

It's also flexibility.