Andrena

The German name is "sand bee", that fits a lot:
"All Andrena are ground nesting, solitary bees. They seem to have a preference for sandy soils.The genus includes no parasitic or social species, though some nest communally or in aggregations. After mating, each female bee digs a burrow, collects pollen to form firm, round provisions for the larvae to eat and places them in cells lined with a shiny secretion. Larvae do not spin a cocoon and they overwinter as adults. They typically have one generation per year and adults are only active for a few weeks. Andrena nests are attacked by many other insects including brood parasitic bees, blister beetles, various parasitic flies" (*Wikipedia)

Thank you H0tamer for hosting Tiny Tuesday in May :-)