sander85

This plugin allows to block spammers with the following options:
<ul>
<li>Block spammers by IPs (supports wildcards).</li>
<li>Block IPs that have posted comments marked as spam.</li>
<li>Block comments that contain bad words.</li>
</ul>
Additional options:
<ul>
<li>If comment contains bad words, add the spammers IP into the blacklist.</li>
<li>When deleting spam, add IPs of spam comments into the blacklist.</li>
<li>Similar entries in the blacklist are merged automatically.</li>
</ul>

Block Spammers

Block spammers from submitting comments, by IPs or by bad words.

maxhaesslein

Block AI Crawlers directly via their IP addresses or user-agents. The blocking happens directly on the server, and not via robots.txt, so it should also block crawlers that do not respect the robots.txt.
This plugin may not work if you use a caching plugin that hooks before the ‘plugins_loaded’ hook. I may add compatibility in a future update.
After installation you need to activate blocking on the plugin settings page. The default settings should suffice, but you can add additional IP addresses, user agents or even JSON endpoints with lists of ip ranges. 
The visitor ip address server variable can also be customized, if your site is behind a reverse proxy and REMOTE_ADDR is not available.
If you want to delete all data the plugin saves in your database, activate the ‘delete all plugin data on uninstall’ option before uninstalling.

Simple AI Blocker

Block AI Crawlers directly via their IP addresses or user-agents.

Block Spammers vs Simple AI Blocker