This burrower bug is present in large numbersin the garden. It probably is the Forget-me-not shieldbug (Sehirus luctuosus) .
This species cannot be differentiated from Sehirus morio, based on photographic material, but only by comparing sizes; S. luctuosus is smaller .
S. morio does not seem to occur in this part of the Netherlands [2,3]. I will measure some of the specimen to be conclusive.
References1 Nederlands Soortenregister
2 Aukema, B., Th. Heijerman & V.J. Kalkman 2016. Veldgids wantsen deel 1. – EIS Kennis centrum Insecten, Leiden.