An old observation that finally got it’s name (thanks to Maarten Willems and Rayan Majoor). It is the larva of the Double-striped pug (Gymnoscelis rufifasciata) [1,2].
There are a number of comparable larva in other species with similar bdorsal pattern and coloration (the color tone can vary over a large range), but the key are the light stripes on the sides.
Here the larva is seen on White melilot, but I haven’t been able to find a relation with that plant. For what I remember the larve was roaming the plant not eating.
References1 Nederlands Soortenregister