drones?

[Drake]

Or, you could check out the Q&A section at http://www.malfador.com/se4.html, where they mention drones specifically (#58)

In general, try and search the Boards or read the Q&A before emailing developers about issues with the game, since the more time they spend answering the same emails over and over from different people, the less time they have to add features, fix bugs, balance gameplay, have a life, etc.

It's easy to miss the Q&A, being on another site. At the very least though, give the search engine on the board a shot. I just did a search on 'drone', and saw this question or some form of it pop up quite a few times...