Hello one idea that I have for you is to use cloudflare. From there you can easily block bots, also, cloudflare is capable of serving many static resources from you to help you save your servers resources. However I believe that it will only serve the static resources once you get a paid plan ($5 or more), the user agent/bad behaviour thing is available on the free plan.
I'll also leave you with these 2 links to check out to do further research.
http://www.fleiner.com/bots/
https://www.google.com/search?q=slow...sm=93&ie=UTF-8