I am a big animal lover, and so animals appear in all of my works in one way or another. Sometimes I throw them in on the side as a loyal pet or, like in The Hollywood Effect, kind of a device to make a harsh character (Gwen) a little more sympathetic, such as when she shows sympathy to a spider. Sometimes, like in The Partial Garden, they are featured more prominently.
When I was little all my stories had animals as the main characters, and books about people seemed so boring. We had an interesting discussion in my Montessori training course about children’s books that star animals. We wondered if children could sympathize more with animals because they were drawn to them in the first place (such as when my preschoolers all flock to the window every time a person walks a dog by). Young children have a hard enough time just identifying and expressing their own emotions that when they see them in other peers and adults they can be confusing and downright scary. Maybe children actually relate more to animals when they act like people than they would if people act like people…or it could just be that animals are cuter and funnier than people. Who knows?
Anyway, even in my adult targeted books, animals still jump in. They make the books more interesting for me to write.