Nice initial implementation of this idea, it's good how the worms rearrange themselves randomly when you eat them and coming back on at the other side of the screen when you go off the edge is handled well too. As for things to see next, a score would be good! And perhaps the movement could get gradually faster as you go on to make things a bit more challenging? Or for something a bit more challenging, you could try implementing a number of levels where you have to get a set number of worms on each one to complete it. Good start though!

What do I have to do? Reach the guy on the motorbike without getting hit by anything else? Incidentally, this seems far too fast at the default speed, try putting something like Greenfoot.setSimulationSpeed(50); in the world's constructor to bring it to something more manageable.

I was wondering if a Greenfoot tetris would appear! Nice work, agreed with delmar about the down arrow and the side movement being quicker - I'd add the rotate could do with being quicker too, by the time I got near the top I was struggling to rotate the blocks fast enough. But it's a really good basic implementation nonetheless :)