Bumblebees are regarded as nice, gentle creatures; even their buzzing has a placid, reassuring sound. They rarely sting and are important pollinators in orchards, on farms and in our gardens. Sadly, however, they are under threat. Many species of bumblebee are on the decline and have been, according to some authors, since the late 1950’s.
Their decline is often attributed to the introduction of intensive agricultural techniques. For example, the introduction of drainage schemes can result in the loss of marsh plants, whilst the removal of hedgerows means not only the loss of plant species but also habitat for bumblebee colonies. The neglect or removal of coppiced woodland, together with the replacement of deciduous woodland with coniferous has resulted in various plant species having a more limited distribution.
Some species of bumblebee like the apple and short haired bumblebee are now believed to be extinct. Those that remain could be under a new threat – namely imported foreign bumblebees! The mediterranean subspecies Bombus terrestris dalmatinus is being used in some commercial greenhouses to pollinate tomato plants (to improve the yield). Some ecologists fear that these imported bumblebees could undermine the genetic make-up of our own bumblebees or even out-compete certain native types. The imported bees can collect more nectar and produce bigger colonies.
There might be another problem for the bumblebees; as numbers decline, they are more likely to inbreed. If a queen mates with a relative, then some of the genetically female eggs develop into sterile males – which contribute nothing to the colony’s present or future.
Like ants, wasps and honey bees, bumblebees are social insects ; that is, they live in colonies. A colony contains a queen, workers and some males (depending on the time of year) but only queens can survive through a winter. The queens usually over-winter underground, or in leaf litter or rotten wood in a specially prepared cell. In spring, they emerge and prepare to make a nest. Some species prepare a nest or colony underground, using something like an old mouse burrow; others create a nest on the surface. The creation of a colony is dependent on the queens, who mated at the end of the previous summer and then over-wintered, being able to forage and find food, build a nest and lay eggs. The pollen, which accumulates on the hairs on the body, is combed off into special pollen baskets on the back legs. Each nest or colony needs a fairly large area over which to forage – without competition.
The first eggs (to be laid by the queen) hatch to give infertile females or workers. They take on the task of foraging and collection of food from the queen. The workers forage (over a distance of about half a mile) for nectar and gather pollen. Different species of bumblebees have different flower preferences, but all bumblebees need to visit a variety of different plant species, as they are active from early spring through to late summer. On a daily basis, they can be seen searching for nectar and pollen from early morning right through to the evening. They are active on days when it is too cold or rainy for other insects to fly – they can warm themselves up ready for flying using something similar to our shivering mechanism. At some point, later in the year, when the colony is bigger, some of the (unfertilised) eggs will produce males, which will mate with the new queens that emerge from other eggs.
To help gather more information about bumblebees, the Bumblebee Conservation Trust has now gained the use of the first bumblebee sniffer dog – called Quinn. He has been trained to locate bumblebee nests, which are difficult to pin point often being concealed in grass and having just a small entrance / exit. Only by mapping the locations of nests can researchers build up an accurate picture of the changes in bumblebee populations. Quinn’s first job will be tracking down bumblebee nests on the Hebrides.
However, we can do our bit to encourage bumblebees. For example, our gardens can offer a rich and diverse supply of nectar producing plants throughout the spring and summer months; species like lavender, rosemary, geraniums, foxglove and heathers are especially attractive. Farmers are also being encouraged to help stop the decline in numbers by sowing a clover mixture around the edges of some fields (Operation bumblebee).