Lucky find.

The Alder Moth is found throughout Britain in damp woods but it is not very common.

This is its caterpillar and we were lucky to see it as it usually feeds out of sight in the tops of trees. In this shot it is on the leaf of Guelder Rose.

The black stalks sticking out from its sides are in fact hairs. But they actually look like oars.
There is a wonderful video on YouTube showing the caterpillar moving across a leaf. The “hairs” look just like the oars on a Viking ship all moving in unison.

I have blipped this once before in August 2015, but as it is a rare find I am happy to give it another go.