You sure can
Go to your blog admin panel and click the settings tab on the far right. Scroll down to the middle of the general settings page and you'll see "Users must be registered and logged in to comment". Check that and save your changes and you'll probably never get spam again.
If that person does register to comment (unlikely) then you can give us their username and we'll ban them.
The vast majority of blog spam isn't posted by humans, but by scripts that automatically search for blogs that are open to commenting without registering.