I have been posting on the Tawny Mining Bees, Andrena fulva, recently. I have been watching suitable nesting sites for signs of activity and today I came across many nests located in groups in several grassy areas. It was a bit windy and the female bees often missed their nests when landing. Instead of walking the short distance, they would fly again, carry out what looked like a positioning flight, and landed on top of their nest mound and got inside.
 Some females seemed to be looking for good places to nest, and tentatively would start digging in the soil amongst other nests.
Males were patrolling around, jumping on passing females. Tawny Mining Bees, like many other bees and wasps, tend to nest in clusters, many nests will be located near each other, when apparently suitable habitat is plentiful around them. They like areas of short grass and the fresh pellets of soil soon stick out like mini mole hills on lawns, verges and park greens.
 Why do bees nest in this way? They are solitary, so each bee will make her own cells and storage pollen and nectar toward her eggs. Apparently bees are able to detect the smell of conspecific active nests and preferable fly towards them; they also tend to return to their natal sites, and, obviously, successful nesting areas would tend to increase their nest density with time. These are proximate explanations, they tell us how bees actually find the nesting sites. But do bees actually benefit from nesting in an aggregation as opposed to doing it on their own? Aggregated nests must have a strong benefit to counteract the costs associated to the behaviour, such as increased competition or higher diseased transmission. Five hypothesis as to the adaptive value of nesting aggregations have been put forward:
1) Bees might be selecting very specific environmental conditions to locate their nests, for example, soil of a particular consistency or nectar sources nearby. This hypothesis has been investigated and appears to hold for some species, but not for others.
2) Nest sites might act as "information centres", where bees would find from others where the best foraging resources where. This, although possible, has no empirical support.
3) Newly nesting individuals might nest in aggregations because they act as markers of successful nesting sites.
4) Bees might benefit from reusing old nests, so that some of the costs of digging would be offset.
5) Nesting communally might offer some antipredator or antiparasite benefits, maybe by confusing predators, or communal defence. Data in support of this hypothesis is conflicting: parasites can either favour aggregations, by being more effective the less aggregated bees are, or dispersed nesting, when they locate clumped nests more effectively. Some bees gain protection from parasites by nesting communally, for example, as I covered in the recent post on Melecta, individuals of the host species Anthophora attack parasites near their nest, therefore conferring some protection to neighbouring nests.
Whatever the reasons, Andrena fulva nesting aggregations must be one of the easiest to observe in British solitary bees. Just look for their little molehills on the grass. A little red head might be peeking from inside.

References
Michener, Charles D. (1974). The social behavior of the bees: a comparative study. Harvard University Press. Other: ISBN-13: 978-0674811751
Rosenheim, Jay A. (1990). Density dependent parasitism and evolution of aggregated nesting in the solitary Hymenoptera Annals of the Entomological Society of America, 83 (3), 277-286

We've enjoyed a few really warm days this week. Bumblebee queens have come out of their winter refuges and are bumbling about looking for nesting sites and feeding on early flowers. Spring bees have also started to emerge, and one of the most striking, the Tawny Mining Bee, Andrena fulva, has also done so. I came across this fresh female flying about and finally settling on the leaf litter to bask. Females are covered on dense and bright orangey-red hairs, contrasting with their black heads and legs. The one below was sunbathing on the bird table in April last year after collecting some cherry pollen. As other Andrena species, females carry pollen in hair brushes on their back legs.
Males are so very different, slimmer, with a large white moustache and more obvious jaws:
This bee flies in a single generation, from late March to late May. The peak flight season on the Tawny Mining bee, April, coincides with flowering times of fruit trees and they can often be seen feeding on them, and contribute to their pollination. They use a diversity of other flowers, including blackthorn, broom and willow.
 The Tawny Mining bee nests in bare patches of ground on grassy areas and therefore is known to nest in gardens and parks. Nesting aggregations, in which many bees nest in the same area, can be quite large and the ground is the peppered with miniature volcanoes of loose soil around the nest entrance which they have dug out while they dig the nest. Despite them nesting near each other, the mining bees are solitary and each female digs her own nest and collects nectar and pollen for her own young. I will keep an eye for their nests, the next few weeks, and see if I can catch them as they come and go from their little volcanoes.