NARRATOR：

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

MALE PROFESSOR：

Okay, so here's a good example of this among ants.

Ants live together in these large nests,

and certain ants, the forager ants,

have a particular job to do-

they go out each day to look for food items... leaves, seeds, fruit...

things like that... and then these ants bring them back to the nest

so all the other ants can eat them.

Now the forager ants don't just bring back whatever they may happen to find;

they bring back different kinds of food.

For example, adult ants normally like to eat things that are rich in sugar

because they need energy to carry on other activities in the nest.

So at a time when the colony is composed mostly of adult ants,

the forager ants look for pieces of fruit and other sugar-rich items.

They bring these back to the nest

for the adult ants to eat to get the energy they need.

But there is a time of the year when baby ants are born.

Now, the baby ants need a different kind of food.

They need food that will help them grow into adults.

So their food needs to be rich in protein.

So now the forager ants do something different.

They start to gather more food items that are rich in protein, like certain types of leaves, or mushrooms.

This way the young ants get the protein they need to help them grow.