Halictus rubicundus (Christ, 1791)
This bee is solitary at high altitudes in Colorado, USA, and possibly Italy as well, but eusocial at lower altitudes in Colorado and elsewhere in USA. Its nesting biology is described by Sakagami and Michener (1962): Nest architecture is Type IIIb: Lateral burrows are very short or absent such that cells are almost attached to the burrow walls at a right angle. The cells are not spatially concentrated in any part of the burrow. Nest aggregation information: 10 in one square meter.