At the end of the book there is this little chart that shows the three parts of a bug and the boys just love this chart. I would have never focused on the three parts with them, but that's what they thought was cool so we went with it.
I made them (very poorly) a bug that they can piece together on the felt board that has all the parts the book talks about. It includes the head, thorax, and abdomen plus the antennae and the 6 legs. I've been pretty impressed at how the boys can make a bug.
They also love the fact that bugs feel with their antennae and not their fingers so we spent lots of time one day crawling around the house like bugs and feeling things with our antennae (wiggling fingers on top of our head)