NARRATOR：

Now listen to part of a lecture on this topic in a biology class.

MALE PROFESSOR：

So, here's a good example of this.

Mites are very small insect-like creatures.

Mites live in tropical climates and feed on nectar and pollen in flowers.

But these tropical flowers don't last long,

they wilt and fall off quickly, and so the mites need to find new flowers in order to get more nectar and pollen to eat.

But the mites can't fly,

and they are so small

that it'd take them a while and a lot of effort to climb down one flower,

crawl to another one,

and climb all the way up again.

So how do they get to the next flower?

Well, there's a bird,

the hummingbird... hummingbirds eat the nectar from the same flowers as the mites.

So when a hummingbird comes around and sticks its beak into the flowers to get the nectar out . . .

the mites quickly climb onto the hummingbird.

Well, as I mentioned, mites are pretty tiny,

so the hummingbird isn't harmed in any way.

And all they do is stick to the hummingbird.

Since the hummingbird also goes from flower to flower for nectar, it takes the mites along.

Once the hummingbird gets to the next flower,

the mites climb off and eat some pollen and nectar there...

on the new flower. Without the hummingbird carrying them from one flower to another,

the mites would find it much more difficult getting food.