Being an Arduino fiend that I am (I own 4), I decided to add one.
This lil bug can do only one thing: move forward. The motor will, literally, only spin one way, so I used the limp to my advantage and forced it to move in a circle. It's behavior is altered by light levels. If it's completely dark, it goes at full tilt. If it's bright (like if a flash light is shone on it), it stops. Anywhere in between and its speed is dependent on the light level.
It DID work, and I'd have made a video, but the gear inside of it has been loosened from the shaft, so the legs will only move if there's no weight on them.
This lil bug uses an Arduino Micro, a darlington transistor, and a photoresistor to make a cheap spider toy move around on it's own. See the circuit in the images.
Ignore the piezo speaker in the picture. I was going to make it chirp or something (feature creep), but then the gear got loose so there wasn't much point.