Hi Sorin,
Don't have any info on ground nesters but you can nest-trap solitaries
that nest in wood by drilling holes 1/4 inch to 3/8 inch in old
2x4's and 4x4's & hanging them about the neighborhood for the summer.
Osmia bees, potter wasps and various other hymenoptera can be captured
in this way.  For a better observation nest, you can cut grooves in
1x4's and make a "sandwich", alternating grooved board, glass (or
clear plastic), grooved board, glass, board, etc.  It's best to plug
one end of the grooves with clay or something similar.  I've used
this nest with orchard mason bees with good results.
 
Cheers,
 
Dave Pehling
 
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