There are three types of worms -segmented worms like earthworms, flatworms like the planarian and roundworms. Roundworms are often parasites. Washing your hands and cooking meat thoroughly are the best things to do to prevent infection from roundworms.
For our biology studies this year, the older boys are using the high school level text, which focuses mainly on the classification, the methods of reproduction and the internal structures of the various organisms we are studying. For the younger boys, I am using the coordinating portions of the elementary zoology series, which goes into more detail. For Alex, we use both texts to give him more exposure to the material. In this way, the whole family can work on the same subject and we can all talk about what we learn together.
The boys thought that the most interesting fact about worms was that planarians tear themselves apart on purpose in order to reproduce. The two halves will then regenerate its missing half to make two complete planarians.