I am not too sure I understand clearly your distinction between ideas and themes, but if you wish to further clarify, please do so by getting back to me. However, the overwhelming idea in this excellent novel is related to the title and the idea of humanity being in a state of transition, like a caterpillar goes into a chrysalis whilst it transforms into a butterfly. Clearly, the central idea that is presented to us is that the human race is in a similar state of transition, with David and his group of telepaths representing the new "butterfly" form that humanity will evolve into and the Waknukians representing the old vestiges of humanity that will soon become extinct. As the woman from Sealand says to the children:
"The living form defies evolution at its peril; if it does not adapt, it will be broken. The idea of completed man is the supreme vanity: the finished image is a sacrilegious myth."
Thus the idea that this novel is based around is that we are not evolved completely as a human species, and that in fact evolution is a constant that we are subject to just as much as other animals in this world.