In the springtime I found this moth caterpillar between dead leafs on the ground during work in the garden, a fifth instar Angle shades (Phlogophora meticulosa) [1] larva. It was not yet active so I moved to a safer spot under a new cover of leafs.
I found this overwinterer on Common mallow but it did not look like it had actually fed on the plant.
Literature
1 Nederlands Soortenregister