The ladybug uses two motors from salvaged hobby servos from which the gears were broken. It does not use any gearbox at all, but relies on the small wheels to have a decent speed. I have to say that this approach works and is also used in some commercial (toy) robot kits ( velleman running bug ). The only drawback I had was the relative high power consumption of the servo motors. The choice of the batteries was limited due to the small size of the body. I had to settle with some non-chargeable button batteries to power the electronics and some AAAA batteries (rather small) for the two motors.
The brains are (again) a AT90S2313 from Atmel, running at 10Mhz, the motor driver is a L293D, a dual H-bridge with build-in clamp diodes.
» That's all