This is a slightly strange Dr. Doolittle book, a bit disjointed and a non-ending, but containing lots of entertainingly told stories within. The book comprises roughly three different themes, although it's allegedly divided into four parts.
The first part of the book tells about a club for crossbred dogs and has several of them telling stories after dinner about their lives. It's quite entertaining.
Then, leaving the dogs behind, Dr. Doolittle becomes obsessed with learning the language of insects, so he contrives an apparatus for doing that, and eventually manages to learn some insect stories, particularly one about a water beetle who was transported in a clod of mud on a duck's foot over to Brazil, and eventually a few years later, back again.
Somewhere in the story telling, Dr. Doolittle hears rumors of giant moths, so quizzes his animal and insect friends for more information about them. Then, quite suddenly, a giant moth shows up in his garden. So they spend the last third of the book (roughly) learning to communicate with the moth, trying to keep the public away, wondering about where to go on a new voyage and whom to take, and so forth.
This story is told through the eyes of Thomas Stubbins who has become Dr. Doolittle's assistant somewhere after Dr. Doolittle's Circus
and before the present book (two volumes that I seem to have missed in my current re-reading of the series). I've always thought the primary fun in the Dr. Doolittle books were the little stories that the animals tell each other within the confines of the major plot themes.