Short story about a boy talking to an alien on this computer

I read this short story in elementary school, 15-20 years ago. I can't remember if it were part of an anthology, or if it were it's own book.

It was written for youth around the age I was when I read it.

The story involves a young boy talking to someone on his computer. As far as I recall, all communication is done through text. The boy types questions, and receives responses back in kind.

The boy figures out he's talking to an alien that needs his help.

The only significant detail I can remember is that the alien mentions something about how all of Earth's animals would react to the alien's presence, and even the most "docile" of creatures, the earthworm, would be a danger to it. It never explains how it would be a danger to it, which I remember bothering me. (I also believe that this was the first time I read the word "docile")