Friday, 25 May 2012

Looking out for bees

On the warming days of spring one becomes aware of the increasing numbers of insects that are on the wing. While a month or so ago it will have been the large queen bumblebees that caught the eye, now many other species can be seen. In the garden, early nectar sources like lungwort, bugle, dandelion and ground ivy are worth watching; more widely, it is the blossom of blackthorn, hawthorn and apple that are worth a glance.

Many of our smaller bees are easily overlooked, not just because of their small size but also because they can prove quite a challenge when it comes to identification. As with the majority of insects these small bees usually lack an English name, a further factor hindering their accessibility to a wider audience.

One of the biggest groups is made up of the 67 or so species that belong to the genus Andrena. These are solitary bees that nest in the ground, hence the common name of ‘mining bee’ sometimes used to describe them. Each female has her own nest, accessed via a tunnel and from which radiate several lateral burrows. Each of these short burrows ends with a nest cell, or small cluster of nest cells, lined with a wax-like substance and holding an egg. Each cell also carries its own ball of pollen, which will provision the larva that emerges from the egg. Many of the Andrena species are rare or have a restricted distribution, but a few are widespread and may be encountered across a range of habitats. Andrena bicolor, for example, is a common species that can often be found nectaring at bramble. It has two broods each year, the first active from March until early June and the second, which is a smaller brood, on the wing from late June through into August.

As is the case with many solitary bees, the nest of Andrena bicolor is sometimes lost to kleptoparasitism (literally, parasitism by theft). In this case, it is another species of small bee that enters the nest chamber and deposits its own egg. The resulting larva kills the egg or larva of the host with its large, sickle-shaped jaws, before eating the ball of pollen.

Other solitary bees are larger in size, approaching the size of a honeybee, and more accessible to the casual observer. Some can be identified from a photograph, perhaps posted on the i-spot website, while others may require a specimen to be sent to an expert. It is possible, however, to identify many species down to the family or genus level, something that might spur you on to get better acquainted with this group of insects. There are even courses to help you improve your identification skills.

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