This is a casemoth caterpillar on the move. This is the first time I've ever seen one not entirely encased in its case. The female moths don't even emerge to find a mate, lazy sods. The Australian ones under the link are more architecturally adventurous, while the kiwi variety contents itself with a few token bits of stick right on the end of its case. Its quite large - for scale, that's the long side of a bit of 50x100mm timber (4x2, or 2x4 for the Americans - I don't know why you guys say it backwards) that it's sitting on.