I have seen these crawling worm robot kits around for some time and always thought they looked interesting, so while I was buying other people Christmas presents, I bought one for myself as well.
It has some neat design features to make it simpler to construction and low cost. The battery compartment comes with a built-in switch. Not a good picture below but you can just about see the lever that you turn to make a contact with the other battery terminal.
It probably took about an hour to put together and it does have some very small screws and some fiddly assembly sequences. Additionally the instructions were in Chinese but by carefully viewing the diagrams on the leaflet and overcoming my fat fingers and less that perfect eyesight I managed to put it together.
A fascinating motion. It truly zips along at some speed.
Technically, it is not a robot as it does not have any sensors or even a controller, but I think it would be relatively easy to add an Arduino of some description, plus a sensor, and then it will be able to interact with it's environment. I wonder if I can connect two or more together to make a much longer worm?