Swarm robotics is a relatively new technology that is being explored for its potential use in a variety of different applications and environments. Previous emerging technologies have often overlooked security until later developmental stages, when it has had to be undesirably (and sometimes expensively) retrofitted. We identify a number of security challenges for swarm robotics and argue that now is the right time to address these issues and seek solutions. We also identify several idiosyncrasies of swarm robotics that present some unique security challenges. In particular, swarms of robots potentially employ different types of communication channels; have special concepts of identity; and exhibit adaptive emergent behaviour which could be modified by an intruder. Addressing these issues now will prevent undesirable consequences for many applications of this type of technology.