Behold the mighty ponderosa pine, nearly a hundred feet tall.

It rises above it all, right?

Except for this little guy, the size of a grain of rice.

The western pine beetle is the nemesis of millions of ponderosa across California.

And she's on a mission: get into this pine tree.

As she starts boring in, it looks like the tree is just standing there, helpless.

But a secret weapon flows beneath its bark.

It's not sap.

It's resin, the tree's defense.

As the beetle digs, the tree oozes resin.

The beetle fights the deluge, going in and out, in and out, to keep the pathway clear.

They trap air under their wings, like a scuba diver, so they can breathe even when they're completely coated.

It's a battle of endurance.

If the tree is healthy, it can produce so much resin that the beetle gets exhausted and trapped as it hardens.

But when there's a drought and the trees aren't getting much water, they simply can't make enough.

She gets in and sends out pheromones to call her friends.

They go straight to one of the tree's most vital tissues: the phloem, a super-thin layer under the bark.

The phloem moves nutrients around the tree.

It's a little bit like our blood vessels.

The beetles eat their way through it, carving these winding tunnels ... which is why their nickname is "drunken beetles."

Eventually, they cut off the flow of nutrients and the tree dies ... millions of trees if it's a serious drought.

And the beetles do even more damage.

They've laid their eggs inside the tunnels.

After their larvae hatch, they wiggle their way out into the bark and finish growing there.

There isn't much to eat in the bark.

But western pine beetle larvae come prepared with their own lunchboxes.

See that white fluffy stuff around this larva?

It's a fungus its mother carried into the tree, a continually growing food supply.

Once the larvae mature, tens of thousands of them bust out of the tree ... and fly off to find new pines to try to start their own families.

Will the beetles succeed?

Or will the trees fight them off?

It'll all depend on the weather.

Water is what tips the scale in this long-running struggle.