It's important to note when reading about botnets that the bot making space is very fluid- platforms and bot populations change constantly- and almost any content you find reporting on bots will have a bias. The research is difficult and subjective without the help of the platforms (twitter, facebook, etc) and we make do with what we can. That said, here are some of the papers and articles I found to be worth mentioning if you're interested in knowing more:

• Social Network Analysis Reveals Full Scale of Kremlin’s Twitter Bot Campaign
• A reasonably in depth yet readable analysis of a Russian influence campaign in 2015
• Correlations and Omori law in Spamming
• This paper covers the use of Omori's law(often used in earthquake modeling) to detect spam or unusual activity
• Don't @ Me: Hunting Twitter Bots at Scale
• Discovery, Retrieval, and Analysis of 'Star Wars' botnet in Twitter
• This paper serves as a walkthrough regarding the discovery and exploration of a massive botnet. The techniques are unique and might not be as successful if applied to a different botnet, but they serve as a great demonstration on how to use OSINT and data science to achieve fascinating results.
• Estimating Bot Populations following the Rich Kids of Instagram
• This article is just fantastic. You really can't go wrong with any of Devin Gaffney's work. I'm not sure how many of the techniques still work thanks to changes with instagram, the overall approach to the data is solid and relevant to the way bots are still being used on instagram.
• IPM
• IPM is doing incredible work and are, in my opinion, in a class of thier own. They have a blog with some lovely, practical examples of the harm bots and botnets can cause, and I highly encourage you to take a look.