If the bot honers it you can create a robots.txt file in your root folder and exclude by agent, ip etc
https://en.wikipedia.org/wiki/Robots.txt
https://ubbdev.com/wiki/view/7/ubb-sitemaps.html

If they do not honor the robots file you can ban them via the htaccess file or the UBB control panel using ip.

If it becomes a ddos attack you need to use something like cloudflare or ask your host about ddos protection.

Blue Man Group
There is no such thing as stupid questions. Just stupid answers