Tuesday, 25 March 2014

Mining bees

It is not much to look at, this short section of bank. South-facing and largely free from grass, it is the sort of bare ground that you’d pass with barely a glance. I suspect that the commuters who park their cars just inches away on this residential road have not even registered its presence.

On this sunny day, however, the eye is drawn to the two dozen or so dark shapes, barely a centimetre in length, that can be seen hovering just above the soil’s surface. Closer inspection reveals that these are mining bees and each is returning to a tiny hole, just a few millimetres in diameter, in which it will lay its eggs. I suspect that the bees belong to the genus Andrena but without catching one and examining it with a hand lens I cannot be certain. The Andrena bees, of which there are 67 species nationally, nest in the ground and are solitary in habits, although they may nest in dense aggregations – such as is the case here on this bank – and they will sometimes share a nest entrance.

Invariably, the nest entrance will lead into a main burrow, from which radiate a number of short lateral burrows, each ending in one or more cells. The cells themselves are lined with a wax-like substance and stocked with a ball of pollen; it is here that the eggs will be laid. The early emergence of this species, prompted by the warm weather, indicates that this is one of the spring species, though some of these may have two broods during the course of the year. The early emergence is helped by the fact that the spring species tend to spend the winter within the burrows as adults, the males emerging a few days earlier than the females.

Even though I cannot put a name to the species from this brief encounter, it is reward enough to see these solitary bees active so close to town. The bank itself is not that high and the bare ground only present because of heavy-handed mowing, underlining the delicate balance of circumstances that has created this opportunity. It also suggests you could perhaps achieve something similar by creating such a bank in your own garden.

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