By Patricia Dung, Target Science Director

Background

You already know that insects (Class Insecta) have one pair of antenna, wings, 6 jointed legs, and three body regions: head, thorax, and abdomen. Thus, you know a bit about all insects, all 700,000 species of them.

Butterflies and moths are insects in the Order Lepidoptera, which means scale wings in Greek. Having scaled wings distinguish butterflies and moths from all other insects. There are 120,000 species of butterflies and moths. We certainly cannot study them all, but if we classify them into groups according to similarities and differences in their structure, we can learn a little bit about all of them.

We often use field guides when we are trying to identify living things. We match our observations with pictures, either drawings or photographs, and descriptions of characteristics. Scientists, however, use dichotomous keys to more exactly identify species.

How are dichotomous keys constructed? Di means two and chotomy means branching. Thus, a dichotomous key has two branches at each level and we must make a choice between two options. Suppose I have a secret card in my hand from a deck of cards. How could you identify the card in my hand? A dichotomous key of a deck of cards might look like this:

Procedure:

Print out the 10 butterfly images and cut along the lines to make 10 cards. Observe the characteristics of the butterflies. What is the shape, size, and color of their wings? Are their distinguishing spots or patterns? What is the shape and size of the body? You can arrange the cards on your desk by grouping those that have similar characteristics from those that do not. Use the dichotomous key of the deck of cards as an example. Use the most distinguishing characteristic first and then move on to the least distinguishing characteristics until you have branches with the number of the butterflies at the end. If there are butterflies that are very similar, the branch would have the numbers of each butterfly in the group. If you have butterflies that are very different from the rest, there will be only one butterfly at the end of the branch. Each of the end branches represent a family of butterflies. Check and see if your families correspond with the Butterfly guide on the Butterfly Dreams web page.