NARRATOR：

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

MALE PROFESSOR：

OK. We can see a great example of this with ants.

Ants live in large groups called colonies.

They normally move together to get to food sources.

And sometimes when ants are moving toward a food source, they'll encounter, uh, find, an obstacle in their path.

So for instance, let's say a large number of ants are walking on a tree, toward some food on a branch.

But, when they reach the end of the branch they're walking on, there's a wide space between that branch and the next one¡ª

the branch with the food on it.

Now, none of these ants alone can cross this wide space to get to the other branch with the food.

So how do they solve this problem?

Here's how.

One ant walks forward until it reaches the end of the branch, and then it automatically holds onto the branch with its back legs.

Then it stretches its body forward into the open space.

Now this comes naturally to ants and it's a simple action...

So then the next ant walks to the end of the branch, and right across the first ant's body.

Then it holds onto the first ant,

and then it stretches its body out into the open space,

just a little bit closer to the branch with the food on it.

Then, one after another, other ants do the same thing,

until enough ants connect together to form a bridge between the two branches.

Pretty amazing, huh?

The connected ants hold this position,

allowing the rest of the ants in the group to cross over this bridge of ants to reach the food.