In the first part of the book, Doctor Dolittle's assistant, Tommy Stubbins, reports on Professor Quetch, curator of the Dog Museum in the Home for Crossbred Dogs.

[1] In the second part of the book, because his garden is teeming with insects, Dolittle decides to learn their language and contrives an apparatus that will allow him to do this.

He begins to hear many fascinating stories, particularly one about a water beetle who was taken to Brazil in a clod of mud on a duck's foot.

Fascinated, he plans a voyage to find them, but one of the giant moths appears in his garden.

The rest of the book is about the doctor's efforts to communicate with the moth, while keeping the public away.