Many Charlotte Mason homeschoolers, especially those following Ambleside Online, know about this fabulous living science book. Handbook of Nature Study by Anna Botsford Comstock, at 887 pages, is an indispensable resource especially if you live in Eastern North America.
Handbook covers many common flora and fauna in the Eastern US. It also discusses how to teach nature studies and includes many interesting activities in each section. While this is certainly a teacher's resource more than a read aloud, Comstock is very interesting to read.
It is not very helpful for identifying backyard finds, but that is not what it is designed to do. Good nature study goes far beyond identification, and this book is rich in information about your finds.
You can download a free electronic copy or purchase a softcover copy through Rainbow Resource for around $20.