Mondo made an “electric roach motel” –

Using a PIC for this device provides a lot of useful functionality. The timing for the power pulse to the inductor is critical to getting the best Zap from your nine volt battery. The longer the current is on, the higher the voltage. Once the inductor reaches saturation, however, you are just wasting power. Some versions of this circuit charged up a capacitor (C1) with multiple pulses. This allowed the PIC to monitor the high voltage and produce a regulated output. Here is the current Source File. The version shown here just generates 400 volt pulses at a rate of 10 per second.

HOW TO – Make a cockroach shocker – [via] Link.