I found this overwinterer, an Angle shades (Phlogophora meticulosa)  caterpillar, on Common mallow (Malva sylvestris) but it did not seem the caterpillar had eaten from the plant.
However, in the following days the caterpillar could be seen on a different leaf and the surrounding leafs had clearly been eaten. The larva clear grew and I found turds, which can be seen on the photo below.
Common mallow is a host plant after all.
References1 Nederlands Soortenregister