The Best Book of Bugs - Claire Llewellyn
This is an overview/introduction on the topic of bugs which offers a nice balance of text to illustrations, but of course that's a kind of relative judgment - very much dependent on the child and their interest level in the material.

The illustrations are a real high point - bright, vivid, detailed - in short I think most children will find them very appealing.

I particularly liked the sections on honey bees, ants, dragonflies and beetles - each of which contained lots of detail. This book does mention centipedes, worms and snails, but doesn't devote a great deal of space to them.