On the West side of Monmouth, along the edge of Sergeant’s Wood and Sergeant’s Grove there are some large nesting aggregations of a small mining bee Lasioglossum malachurum, sometimes called the Sharp-collared Furrow Bee on account of its square ‘shoulders’ which can just be seen with a hand-lens. (‘Furrow’ refers to a groove in the last abdominal segment of the female, characteristic of all Lasioglossum and Halictus bees.) It is a common bee in the Monmouth area, though at only 7 millimetres long it doesn’t fit everone’s idea of ‘bee’ and is easily missed.
Besides being gregarious – having many nests in one place – this bee is truly social though not on the scale of honeybees and bumblebees. In each nest, the founding queen and her daughters co-operate to forage and raise the next generation. It has been much studied by evolutionary biogists because of what it can tell us about behavioural origins of social living. There is a good article on it in Wikipedia.
The largest aggregation contains about 1500 nest holes, which I counted using a metre square, though there may be up to twice this number, since many are hidden by vegetation or beyond the margins of the measured area.
The Field Guide to the Bees of Britain and Ireland, says that Lasioglossum malachurum ‘is not recorded from . . . Wales’.