Spider Blocker will block the most common ones and allow you to manually add your own. It will accomplish this by using Apache .htaccess file to minimize impact on your website.
Spider Blocker leaves no footprint on your WordPress blog.
The plugin is open source and completely free. It can be downloaded directly from WordPress.org.
Why use Spider Blocker?
If you're in a highly competitive niche, competitors will spy on your website, review your backlinks and use it against you. They can try to replicate your backlinks or even report your blog network and links to the Spam Team.
Spider Blocker prevents that.