There are millions of different living things in the world. Just how many there are, we have no clear idea, but we can try to sort them all out into groups by looking at how they differ from each other.
For example: insects are animals with six legs. No other type of animal has six legs and any animal that has more than six legs or fewer than six legs can't be an insect.
So, is a spider an insect or not? Count its legs!
In this worksheet we'll look at some of the ways we can group different living things.