You might want to look at project honeypot (https://www.projecthoneypot.org/)

They are an open and distributed service that uses various signatures (ip, tar pits, etc) to block spammers and bots on your site.

I put it up on one of my sites and saw an immediate drop to almost nil. I went from 100+ spammy messages a day to less than 20 in the last 3 months.