bgribaudo

Attempts to prevent automated SPAM by requiring visitors to answer a question of your choosing in order for their comment to be accepted. Presumably, spambots will be unable to correctly answer this question and so comments they attempt to post will be rejected.
Only regular comments from non-logged-in users are filtered. Pingbacks, trackbacks and authenticated users will not be prompted to answer the verification question.
Privacy Note: This plugin does not call home or communicate with any external servers or services. All processing is done locally within your WordPress site.

Super Simple SPAM Stopper

Prevents automated SPAM by requiring visitors to answer a question of your choosing (plaintext or regex).

poku

“Block Spam Comment” definitely blocks comments of bots without settings or Captcha.
The three systems of “Block Spam Comment” using JavaScript make it impossible for bots to post comments, because bots cannot use JavaScript. Spam comments are not saved, so it reduces load on your server and save time to delete spam comments.
You can see how many spam comments were blocked and data about IP and user agent of bots. You also can download the csv file with that data.

Block Spam Comment

Block spam comments definitely without settings or Captcha.

Super Simple SPAM Stopper vs Block Spam Comment