Very interesting topic indeed
Some solutions exist to help
for example you can use an API or JsTag solution from
https://forensiq.com/ to detect threats. Suspected bot traffic start at 70% threat and the high risk at 80%. You can decide to send back or filter that traffic at the source
Another solution is
Block Bots and Stop Web Scraping | Distil Networks. Works great, the only issue is that they do not fully support adult sites on their own servers. So they offer adult sites their server based solution only.
The good thing about both companies is that they charge based on queries (volume)
One thing is certain, in 2016 you cannot do nothing against bots