Parasite in the Poo

In the desert world, water thieves can come in many forms

to exploit even the smallest chink in a plant's defense.

One of the strangers travels within the gut of a fruit-eating mockingbird.

These are the seeds - the tristerix -

a kind of mistletoe.

Their goal is the water inside this hedgehog cactus.

Using the spines as anchors, the seeds start to germinate.

Each produces a long probe with which to try and locate the cactus's skin.

For most, that's a stretch too far and they perish.

But for this one, the cactus's surface is within reach.

It clamped onto it with a special sucker

and then waits for darkness.

At night, the cactus opens its pores in order to respire.

Oxygen goes out, carbon dioxide goes in

and so does tristerix.

Once within, its tissues spread throughout the body of the cactus,

sustained by the precious store of water that they find there.

Then a year later, it breaks through the cactus's skin

and bursts into flower.

Hummingbirds come to drink their nectar

and pollinate them as they do so.

And then, to complete the cycle,

tristerix produces hundreds of white eye-catching seeds,

ready to be carried away by a bird to invade another cactus.