At the top of the mound I immediately found many hundreds of bees flying just above the ground. They were mining bees, Andrena nigroaenea. The female makes a nest in the ground with the entrance surrounded by chalk spoil looking like a miniature volcano. There were so many that I had to take great care not to tread on them. Some were made right in the paths that run along the ridge. Some holes were dug into a small cliff.
The female bee is about the size of a honey bee but hairier and orange/brown in colour. She forages for pollen and nectar to feed the larvae which hatch from the eggs she lays underground. The larvae pupate and remain underground until the following spring. The pollen is collected on the hairs on the hind leg - the scopa - a bit different from the pollen basket (corbicula) on a honey bee.
Each female has her own nest and remembers where it is, although they seems to spend some time looking for the right spot on their return, probably because there are very few landmarks. This one is carrying pollen.
This bee is about to enter the entrance to the nest below.
The male is smaller, slimmer and darker in colour but with paler hairs. Males seem to spend most of their time hunting for females or sitting in the sun but they also forage for nectar.
Mating often involves one female with many males attempting to mate with her. Here there is just the one.
Mining bees are solitary bees. Every female is fertile and has her own nest. The adults die after a few weeks and the next generation remains underground until next spring. Andrea nigroaenea is a fairly common bee and is also known as the Buffish mining bee.