We demonstrate that an interferer with malicious intentions can significantly degrade the performance of impulse radio (IR) ranging. The cicada attack we have developed can decrease the distance (degradation of service) measured by ranging algorithms designed to cope with weak NLOS conditions; it can also jam communication (denial of service). The attack is easy to mount and can be effective even against receivers designed to cope with benign multi-user interference. We also sketch possible countermeasures.