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Gardening for Bumblebees

Published in an October issue of  Organic Gardening Magazine

If bumblebees hadn’t been invented I have no doubt there would now be a mythical version – the cute and cuddly equivalent of a dragon or the fairies that as children we imagined were at the bottom of our gardens.  What could be nicer than a round furry flying creature with a gentle droning buzz, a striped coat and a docile nature? Perhaps we would omit the sting (and anyone who has been stung by a bumblebee will know that it is every bit as painful as a honeybee’s) but other than that the bumblebee for me is the perfect insect, and I forgive it the occasional act of self defence.

Gardens can be wonderful habitats for bumblebees and are well used by these insects when the conditions and the plants are right for them. It is now well documented that around half of our 24 native species are declining rapidly in the wild and one has probably become extinct in recent years.  Sadly good nesting sites and suitable nectar and pollen producing plants are in ever-shorter supply in the countryside, plus the widespread use of insecticides in farmland has taken its toll of bumblebee numbers.  Our gardens have become important refuges for these insects but we need to take positive steps to ensure that numbers increase.  With some garden wildlife it can be enough to do very little except create areas where creatures can go about their business undisturbed.  With bumblebees we have to be a little more proactive in our planting, plus it is possible to create areas where they can build their nests once we know more about their habits.

Apart from the aesthetic reasons for encouraging these insects (and what garden doesn’t look better for being full of life?) bumblebees are beneficial to the grower.  They are essential for the pollination of certain crops, both commercially and in our gardens. 

 Bumblebees are of great economic importance pollinating a wide range of food crops including tomatoes, beans, peppers, aubergines, kiwi fruits, soft fruits such as raspberries and strawberries, plus apples and plums.  Commercial tomato growers introduce these insects to glasshouses and poly tunnels where their unique form of pollination – vibrating their wing muscles at a specific speed to encourage the tomato flowers to release their pollen – provides a very efficient means of setting fruit.  Any allotment holder knows the value of having plenty of bumblebees around and with the alarming decline of honeybees due to Colony Collapse Disorder and other causes, we need to take greater care of these natural pollinators.

Like all garden wildlife bumblebees need a few specific requirements to flourish and thrive.  Food in the form of both nectar and pollen is essential and a place to nest and reproduce is vital.  Both of these requirements can be met by the determined and interested wildlife gardener although the former is rather easier than the latter!  Bumblebees are notoriously difficult to tempt into artificial nests, but with a little thought there are plenty of things we can do to make potentially attractive natural nest sites for them.  In order to do this well is it useful to know a little about the bumblebee life cycle.  It is quite extraordinary to think that at this time of year queen bumblebees may be around in your garden searching for a suitable underground place to hibernate for the winter months, not emerging until next spring.  Having mated in the late summer she may use a hole she has found, or excavate an underground cavity herself.  Here she will stay right through the winter months until the warmth of the spring sunshine in March or April wakens her.  She emerges from her chamber and begins to search for food – she needs both pollen and nectar to build up her fat reserves.  Her next task is to find a suitable nest site.  Queen bumblebees are often seen in the spring, zigzagging across the ground searching for somewhere to lay their first eggs.  She will be especially seeking an old vole or mouse nest which she can detect by its smell, but the proximity of a good foraging area with plenty of nectar and pollen producing flowers will also influence her choice.  She needs to make sure that there will be available food for her offspring not too far away.  If a old nest is not found she will build her own in a hole in a bank or in dead vegetation but the location will vary with species. 

The carder bees are a type of bumblebee that will tease out and pull together mosses and dried grasses to make their nest (hence their name – carding being the process of combing wool before spinning) so are more likely to be found in compost heaps.  Other species will chose a hole in mossy or grassy bank, or occasionally a disused birds nest, even if it is in a nest box.

When the nest is ready the queen will collect pollen which she forms into a mass and on which she lays her eggs.  Once the eggs have hatched she tends the larvae with great care, keeping them warm with her own body.  They grow and eventually pupate, emerging as smaller versions of their mother in a few weeks.  The queen continues to lay eggs and the new worker bees collect food as the colony size increases.  It is not until the summer that male bees are produced together with new queens.  These mate, the males die (as do the workers and the old queen) leaving only the new young queens to find a home, survive the winter and begin the cycle again.  As gardeners we can help these useful bees during their short lives.  Ensuring that they have a good selection of plants to provide the nectar and pollen they need is relatively easy.  Some of our most attractive cottage garden plants will attract bumblebees and it is no hardship to include a good selection of these in our gardens.  Foxgloves, hardy geraniums, Verbascum, Antirrhinum, Campanula and poppies are all excellent bumblebee plants.  They also love the flowers of Buddleia (especially Buddleia globosa) and many other shrubs including Hebe, pussy willow and Ceanothus.   A wildflower meadow will hum with bees if it contains knapweed, clover, bird’s foot trefoil and field scabious.  Other useful wildflowers are the woundworts, mints many other members of the Labiate family, thistles, comfrey, vipers bugloss and heather. 

Helping your bumblebees to nest is another matter.  Many types of bumblebee nest home are available, but unlike the solitary bees which will readily use artificial nest homes, I have never managed to encourage bumblebees to use these nest boxes, or for that matter heard first hand of anyone who has!  However I have had plenty of nests in my gardens especially where grass, left to grow long, has encouraged small mammals.  Their redundant nests have been used readily by bumblebees in many situations.  In my previous dry garden they would take over any empty nests especially on the edges of meadows or areas of undisturbed grass beneath hedgerows.  In my current wetter garden mammal nests on well-drained banks and slopes have been used, which seems to make sense as the flatter areas are more easily waterlogged in wet conditions. 

Wildflower meadows are especially good habitats for these bees as they provide both nest sites and food plants, so if you do want to encourage more bumblebees to pollinate your fruit, veg and flowers create a bumblebee meadow with a good selection of wildflowers known to be attractive to these useful insects.  This can be done in a variety of ways but even an area of long grass, a corner of a lawn left to grow or grass running up to or beneath a hedge could be sufficient.  Although bumblebees will forage for up to half a mile for pollen and nectar, the close proximity of a border with a good selection of flowers including labiates, daisies, globe thistles, poppies and foxgloves will influence the choice of nest site.  Further inducement to nest could be to create holes in bank and push into each one a loose bundle of moss about the size of a tennis ball.  A sheet of corrugated tin laid on the ground in an out of the way place might also tempt a carder bee queen to create a nest beneath it.

When gardening for wildlife it is important to provide natural food for your garden visitors throughout the period when they may be around.  This is especially true of the bumblebee – the queen in particular needs pollen and nectar when she emerges in the spring.  Her survival at this time is paramount, so make sure you have plenty of dead nettles, lungwort and bugle, Berberis, Cotoneaster, flowering currant and pussy willow in the spring.  Lastly leave dandelions wherever you can and she could well reward you with a nest of young bees ready to pollinate your fruit and vegetables.