It was a gloriously hot sunny April day high in the Peak District hills around Flash in Staffordshire. We were standing on the steep bank of a stream where off road motorcyclists (judging from the tyre tracks) had created a large area of bare sandy soil around the gritstone rocks. As we were perusing the map we became aware of some 30 to 40 small dark insects milling around our ankles – although showing no aggression towards us. Each time we shifted our feet they would rise as one, but the minute we stopped they would resettle again.
They were Halictus rubicundus – a type of ground nesting bee, no more than 1 cm in length and with narrow white bands on their black abdomens, and yellow hind legs. As we looked more closely we could see a number of small holes peppering the bank amongst the rocks. We had obviously stumbled upon a favourable site where the bees normal nesting requirements of having vertical and/or sloping bare ground, which faces south, and has compacted sandy soil were fully met. The insects seemed to be inspecting the holes and either backing out quite quickly, or disappearing inside. In one or two places you could see a bee in the process of excavating a hole and pushing soil out with its hind feet. There were also mini spoil heaps beside some holes. .
Unlike honey and bumble bees, which are both social insects, Halictus rubicundus can be either social or solitary in its behaviour, or even a mixture of the two. Social insects live in colonies, and work for the benefit of others in that colony, whereas solitary insects work for themselves and their offspring. Whether they act socially, individually or in a mixture of ways seems to vary in different climactic areas. Generally warmer conditions allow for a queen bee to lay two broods in a breeding season and act socially. Whereas colder conditions only allow for one brood to be reared and therefore the queen and her offspring to act in a solitary way.
For Halictus rubicundus that are acting socially, the queen bee emerges from hibernation in April, and then looks for a suitable nest location, which may not be far from where she spent the winter. There she will excavate a vertical burrow around 7 – 12 cm deep, with very short (2 – 10 mm) side tunnels leading to some 5 – 7 cells. Within each cell she will then place a ball of pollen and lay a single egg on it. If successful this first brood will emerge from May onwards and consist of female workers, which will help the queen to forage and provide for a second brood. This second brood would be provided for in new cells some 5 – 10 cm deeper than the original cells. Males and new females would then emerge from July to October. In colder environments the queen will lay one reproductive brood consisting of both new females and males.
In those environments that are marginal between warm and cold conditions, the queens can produce some female workers (that will help to rear a second brood) and some females (that can go on to hibernate at a slightly earlier date) – thereby in effect “hedging her bets”. This strategy has proved highly successful and today this type of bee is found throughout the holarctic area of the world i.e. in non tropical Europe and Asia, in Africa to the north of the Sahara, and across North America to the north of Mexico's desert area.
As the bees that we came upon were out and about in April (albeit a very sunny April), I think they were acting in a social manner. It's pleasing to think that such small animals are so successful on a global scale and that we had a chance to see a little of their lives.