Thursday, 20 February 2014

The rise and fall of a White-tailed bumblebee colony

On a mild day at the beginning of March the White-tailed bumblebee queen (Bombus lucorum) emerges from hibernation. She has slept buried in the soil under the hedge since last autumn and is now very hungry. The sun is shining and early spring flowers such as Crocuses, Winter aconites, Lesser celandine (Ficaria verna) and Snowdrops have opened their flowers. The queen has soon found a nice patch of crocus flowers on a nearby allotment site and is now eagerly drinking the nectar hidden at the bottom of the flowers.
She finds more early spring flowers in the surrounding gardens and after a few days of feeding she feels revived and ready to search for a suitable nesting site.

The bumblebee queen drinks nectar from a crocus flower

The entrance to the bumblebee nest
The allotment site looks promising so she flies low over the ground along the surrounding hedge, along paths and over plots with rough grass to look for old abandoned mouse nests, her favourite nesting places. She finds an interesting hole in the ground and lands for a closer inspection. But no, the location is too shady so up she flies again looking for a better nesting site. Some more suitable nesting places she finds are already occupied by Buff-tailed bumblebee queens (Bombus terrestris) and as they are much bigger than her she will not risk a fight.
Finally, after a few days of searching, she has found what she was looking for; a nice old roomy mouse nest on a south-facing grassy bank. She inspects the hole carefully and after a while takes up residence. 
Brood cells and wax pots (for storing nectar & pollen)
Now she needs more nectar and pollen so she can start building her nest. The queen flies busily back and forth between nearby patches of early spring flowers and her nest and brings back great amounts of pollen and nectar. The nectar she stores in a wax pot she built herself (she secretes the wax from her body) and forms a small mount with the pollen.
When the queen has collected enough nectar and pollen she starts to lay her first eggs on the mount of pollen which she covers which a layer of wax. She now needs to keep the eggs warm so clambers on her nest and starts shivering her muscles to produce body heat. From time to time when she feels hungry she sips nectar from her wax pot. If the queen is running out of nectar she has to leave her nest to collect more but as her brood will cool down when she is not in the nest she has to be quick. Luckily there are big patches of spring flowers nearby so she has not to fly far. 

The queen collects pollen from a Pasque flower (Pulsatilla) nearby
The little white grub-like larvae hatch after several days and the queen feeds them with nectar and pollen she collects near the nest. After about 2 weeks the larvae have grown considerably and are spinning a cocoon in which they develop into adult bees.

The queen’s first offspring will all be workers which will help her in the nest, raise the next batch of workers, guard the nest entrance and go foraging for nectar and pollen. To create workers the queen releases a pheromone which signals the larvae to develop into worker bumblebees. As soon as the first workers have hatched the queen will stay inside the nest (this is much safer than to go foraging herself) and concentrates on laying more eggs. 

A worker foraging for pollen and nectar
It is a warm spring and early summer and the colony, surrounded by many pollinator-friendly flowers, is growing and growing. The nest contains now more than 200 workers and is a hive of activity. The bigger worker bumblebees have the task of foraging for nectar and pollen or guarding the nest entrance while the smaller workers help the queen to feed the larvae and keep the nest warm and clean.
A gang of sinister-looking cuckoo bumblebees
Several times now the bumblebee guards at the nest entrance had to fend off a Gypsy cuckoo bumblebee (Bombus bohemicus) female which was trying to enter the nest with the intention to kill the queen and to take over the colony. But so far the cuckoo bumblebee did not manage to get past the bumblebee guards.

The neighbouring Buff-tailed bumblebee colony did not get so lucky and is now ruled by a Southern cuckoo bumblebee (Bombus vestalis) female. The cuckoo bumblebee managed to sneak past the guarding buff-tailed bumblebees at the entrance and hid at the bottom of the nest for a while before killing the queen and taking over the nest. All the remaining Buff-tailed bumblebee workers have now to work for her new cuckoo bumblebee "queen", collecting nectar and pollen and feeding it to her offspring.

The workers like to forage on Phacelia flowers

A White-tailed bumblebee male
It is now mid-summer and the old queen in our White-tailed bumblebee colony is getting weaker. She stops to produce the pheromone which signals the larvae to develop into worker bumblebees and all the eggs formerly destined to become worker bumblebees will now develop into new queens. The queen larvae will consume more food and grow a lot larger than the worker larvae so it is putting quite a strain on the resources of the colony to raise new queens. The queen is also running out of sperm with which she has fertilised all her previous eggs (fertilised eggs always develop into females) and now lays another batch of eggs which she does not fertilise. These eggs will develop into males.  
A worker (left) and a male (right) visiting Wild marjoram

The remaining workers will help the queen to raise the last offspring but as the queen gets weaker she starts losing control over her daughters which will subsequently become more unruly and disobedient. Whereas previously the queen maintained a strict command over her workers she can now not prevent her daughters from laying eggs themselves (all worker bumblebees are fertile so can theoretically lay eggs). Eggs produced by workers will always develop into males as worker bumblebees have never mated with a male. But fortunately for the queen only a few of her daughters eggs will hatch into adult males, so most males produced in the colony are still her own sons. 

A young queen drinking nectar from Cosmos flowers
In late summer the young queens hatch and leave the nest to look for mating partners. They will still come back to the safety of the nest each night but often forage for themselves during the day. The males have hatched as well and after a few days in the nest, drinking from the stored nectar but otherwise doing nothing to help with the nest routine, leave the nest for good. They now spend the rest of their lives looking for a young queen to mate with.
To find the queens they often patrol along a certain route, often in tree tops (different bumblebee species patrol at different heights); scent-marking prominent objects along the way such as tree trunks with pheromone. In the rare cases a young queen comes along they mate with the often much larger queen, clinging to her back and after transferring the sperm sealing her genital opening with a plug so that she cannot mate with another male. As there are more males produced than new queens many males never get a chance to mate so they just hang around on flowers and drink nectar until they die. 

After the young queens have mated they will concentrate on drinking a lot of nectar to fill their honey stomach and to build up their body fat. It is crucial for the young queens to find enough food before colder weather sets in to be able to survive hibernation.

Young queens need to drink a lot of nectar before they hibernate

In the meantime back at the nest the old queen dies together with the last of the workers. The nest lies empty and will not be reused by the young queens in the next year; they will always build a new nest to avoid a build-up of pest infestations. 

The young queens are now on their own and will start looking for suitable places to hibernate. Good places to hibernate are in loose soil under tree roots, hedgerows and at the base of walls. Once the young queens are safely buried in the soil they will not emerge until late winter or early spring of the next year. Some of the young queens will not survive hibernation but the ones which do survive will emerge in late February or March and start the cycle all over again.

If you are interested in further reading about bumblebees I can recommend the book “A Sting in the Tale” by Dave Goulson. This book is not only a great way to learn more about bumblebees and the most recent bumblebee research but it is also hugely entertaining and a real page-turner.

I know the nectar must be here somewhere ...

Monday, 17 February 2014

Bumblebee queen acrobatics

Now is the time bumblebee queens start to emerge from their hibernation places and the first you will see are often Buff-tailed (Bombus terrestris) and White-tailed bumblebees (Bombus lucorum). The queens are hungry after their long hibernation and in urgent need of food in form of nectar from early spring flowers such as Snowdrops (Galanthus spp.), Lesser celandine (Ficaria verna) and Crocuses (Crocus spp.).
I have planted quite a lot of crocuses on my allotment and every year in February and March I can watch hungry bumblebee queens visiting the flowers. It is quite interesting to see what acrobatics the big queens perform to reach the nectar which is hidden right at the bottom of the crocus flowers. But it must be worth it as the queens spend up to several minutes in a crocus flower, often head first, and in the process get loaded with loads of crocus pollen.
Below are some pictures of a White-tailed bumblebee queen visiting a patch of crocus flowers on my allotment. The mites you can see in the pictures, clinging to the queen, are normally quite harmless. They live in bumblebee nests and eat wax, pollen and debris. The mites in the picture have hibernated with the bumblebee queen and are now hitching a ride so they can settle down in the new nest the queen will start building soon.

Wednesday, 5 February 2014

Wild plants for pollinators

There are hundreds of garden plants available and many of these plants are good for pollinators. You could fill an entire garden with them but most of these plants are not native and often hail from far-off regions mainly in Asia and North America.

The flowers of non-native garden plants are often similar enough to our native plants to be visited by many pollinators such as bumblebees which are often not very specific about the flowers they visit. But there are some specialised pollinators which only visit specific flowers such as the Harebell carpenter bee (Chelostoma campanularum) for example which only visits Harebells (Campanula rotundifolia) and a few other bellflowers. Also some native wildflowers such as dandelion (Taraxacum agg.) and clovers (Trifolium spp.) seem to attract a lot more pollinators than many garden plants and are a very important food source particularly if other flowers are scarce. Some native wildflowers can look as pretty and showy as garden plants but often you have to take a closer look to appreciate the delicate beauty of native wildflowers.

Wildflowers are also often quite low-maintenance, tough and disease resistant if grown in the right conditions and pollinators will find your garden even more attractive if they can spot some wildflowers in between the garden plants.

Harebell carpenter bees are only collecting pollen from a few bellflowers

So why not include some native wildflowers in your garden? Some are pretty enough to deserve a place in your border, others could be grown in a less-visited corner of your garden which you could also leave a bit wild. Allow your lawn to grow a bit longer, at least in some parts of your garden, to encourage Lawn daisies (Bellis perennis), clovers and dandelions to flower. If you have a pond you could plant some native pond/bog plants such as Marsh Marigold (Caltha palustris), Water forget-me-not (Myosotis scorpioides) and Ragged robin (Lychnis flos-cuculis).
You could even sow a little wildflower meadow in a sunny area of your garden. Have a look here for some instructions.
Below are some suggestions of what native wildflowers you could plant in your garden. For more ideas also have a look at the RHS (Royal Horticultural Society) Perfect for Pollinators Wildflower list.

Wild marjoram (Origanum vulgare)

Probably one of the best plants for pollinators in my opinion. Especially bees and butterflies like the pretty pink flowers which open in July and August. Growing on calcareous grasslands in the wild the plant is quite adaptable and will grow on most ordinary garden soils as long as they are not waterlogged. Wild marjoram needs a sunny position on well-drained soil.
 Read more about this plant here.

Harebell (Campanula rotundifolia)

A pretty plant with delicate bell-shaped flowers and small leaves. As the plant is quite low-growing and not very tolerant to shading it is best positioned at the front of the border or in a rock garden. Harebells need a sunny position and well-drained soil.

Lawn Daisy (Bellis perennis)

Leave your lawn to grow a bit longer and you can enjoy these little beauties for much of the year. Solitary bees such as the Tawny mining-bee (Andrena fulva) like to visit the flowers in spring.

Forget-me-not (Myosotis sylvatica)

A Bee fly visiting the flowers
This is a biennial plant and forms clumps of hairy dull-green leaves in the first year which erupt in masses of small blue flowers in April and May of the second year. Forget-me-nots self-seed prolifically so once you have a few plants you will never be without them. The plants look pretty in a natural setting under deciduous trees together with spring bulbs such as wild tulips and daffodils.
Many pollinators visit the plants such as solitary bees and bee flies.

A mason bee (Osmia bicornis male)

Wild roses such as Dog rose and Field rose (Rosa canina, R. arvensis and others)

These shrubby plants with long thorny shoots fit best in a wildlife hedge or planted between other flowering shrubs along a fence or wall. The white to pinkish flowers open in June followed by edible rose hips. Bumblebees and other bees like to visit the flowers.

Dandelion (Taraxacum agg.)

Not everybody`s favourite plant, dandelion has its uses, especially for hungry pollinators in spring. If you do not want it to seed around your garden just remove the faded flowers before they set seed. You can even eat the leaves if you are after some fresh produce from your garden. Read more about this plant here.

Meadow buttercup and Creeping buttercup (Ranunculus acris and R. repens)

Especially the Meadow buttercup is quite a pretty, relatively tall plant with glossy yellow cup-shaped flowers. Creeping buttercup looks somewhat similar but is much lower growing and creeps along the ground with long running stems which root at the nodes. Both like heavy wet soil and do not mind if the ground becomes waterlogged in winter. Bees and hoverflies like to visit the flowers.

Ragwort (Senecio jacobaea)

Ragwort is quite a controversial plant with some advocating to eradicate it as soon as it pops up somewhere. But this does not do the plant justice as it is an excellent plant for all sorts of pollinators from butterflies to bees, hoverflies and beetles. As long as you do not make hay intended to be fed to horses and other livestock from the area where Ragwort is growing it is save to have it in your garden as these animals would not eat the fresh plants. Ragwort grows in sun and light shade on all ordinary garden soils.

English poppy (Papaver rhoeas)

These cheerful and pretty flowers are well-worth having in your garden. The seeds need to be sown on open fertile ground without much shading and competition from other taller plants (think of arable fields and disturbed ground as their natural habitat). The plants are annual but self-seed in suitable conditions. Bumblebees and hoverflies love the flowers.

White and Red deadnettle (Lamium purpureum and L. album)

These are great plants for bumblebees as the flowers produce a lot of nectar. The plants grow best in sun or light shade on fertile ground. They are best suited to a wild corner of your garden but White deadnettle can be pretty enough to include in a more informal flower border.

Hairy-footed flower bee visiting a Red deadnettle flower
White deadnettle
Red deadnettle and Common field speedwell look pretty together

Viper`s bugloss (Echium vulgare)

This is a biennial plant which produces a basal rosette with long prickly leaves in the first year and a tall flower spike with blue to purple flowers in the second year. The plant needs a sunny position on well-drained soil and is best sown from seed as established plants do not like root-disturbance. Bumblebees are very fond of the flowers and you will see them flocking to your garden once you have some Viper`s bugloss in flower.

Wild carrot (Daucus carota)

A pretty plant with feathery leaves and tall white umbels from August to September. It has a long tap root and can withstand drought for quite a long time. The plants need a sunny open position on well-drained soil. The flat open umbels are attractive landing platforms for many different pollinators and you will see hoverflies, solitary bees and beetles visiting the flowers.

Myatropa florea, the batman hoverfly

Field scabious (Knautia arvensis)

A tall plant with pretty purple flower heads. Well-suited to an informal flower border. Needs a sunny position and fertile ground. Pollinators love the flowers and you will see bees, butterflies and hoverflies visiting.

Cowslip and Primrose (Primula veris and P. vulgaris)

Both plants a great plants for a spring flower border or naturalised in grass or under deciduous trees. They normally flower in March and April (Primrose can flower earlier in a mild winter) and are great for early pollinators such as Hairy-footed flower bees and other solitary bees and bee flies. Cowslips and Primroses should be planted on fertile moist ground which does not dry out too much in summer.

Hairy-footed flower bee visiting a Cowlip flower
A Bee fly on a Primrose flower

Ivy (Hedera helix and H. hibernica)

A great plant for late pollinators as it is one of the latest native plants to come into flower, normally in September and October. Read more about this plant here.

Devil's-bit scabious (Succisa pratensis)

Flowering very late in the year, normally in September and October, this plant is often visited by late-flying pollinators, especially butterflies. Devil`s bit scabious is pretty enough to be planted at the front of a flower border but it needs to grow in soil which does not dry out in summer. The plant can even be grown in a boggy but sunny corner of your garden as it does not mind to grow on soil which becomes easily waterlogged.

Red and White clover (Trifolium pratense and T. repens)

Leave your lawn to grow a bit longer to give Red and White clover the chance to flower. Both plants need a sunny position and are loved by bumblebees.

Rec clover visited by a Common carder bee (Bombus pascuorum)
A field of White clover

Spear thistle (Cirsium vulgare)

This thistle has quite large purple flower heads which are very attractive to bumblebees. Often you can see several bumblebees fighting for space on one flower head. It is a biennial plant and produces a large basal rosette with spiny leaves in the first year and purple flower heads on tall stems in the second year. The plant needs a sunny position and is best suited to a wild corner of your garden as it self-seeds prolifically.

Blackberry and Bramble (Rubus fruticosus agg.)

A large shrubby plant with long spiny stems and pretty white cup-shaped flowers in June and July which are visited by bumblebees, solitary bees and hoverflies. The large plants are best suited for planting in a wildlife hedge or in a wild corner of your garden. If you do not want to grow the wild bramble you can get some cultivated blackberries which are a bit better behaved and can be trained to a trellis. You can also enjoy delicious blackberries in late summer.

A Leafcutter bee (Megachile sp.) on a bramble flower

Ox-eye daisy  (Leucanthemum vulgare)

The large white daisy flowers with a yellow centre look pretty enough to be included in a flower border. The plant needs to be grown in a sunny position on fertile ground. Bees, hoverflies and butterflies love the flowers.

Musk mallow (Malva moschata)

The large pink flowers of Musk mallows are great for bees as they contain a large amount of pollen. This plant is well-suited to a flower border but you should take care that the plant is not overshadowed by taller perennials as it needs a sunny open position. It will still grow in light shade but flowers better in the sun.

Purple loosestrife (Lythrum salicaria)

A tall plant with showy pink flowers. Best planted on permanently moist or wet ground in full sun (for example the edge of a pond) as its natural habitat are river banks and wetlands. Butterflies and bees are fond of the flowers.

Black knapweed (Centaurea nigra)

This plant looks great in a wildflower meadow or in an informal border. It needs a sunny position on well-drained soil. The large pink flower heads are visited by butterflies and bees.

Bird`s-foot trefoil (Lotus corniculatus)

A small delicate plant with quite large yellow flowers which often have a red tint. It needs a sunny position on well-drained soil. Bird`s-foot trefoil grows well in short grass on quite dry, rather poor soil. The flowers are very attractive to bumblebees.

Other good wild plants for pollinators are Teasel (Dipsacus fullonum) and Evening primrose (Oenothera biennis). Both are biennial plants with basal rosettes in the first year and a tall flower spike in the second year. They need a sunny position to flower well. Evening primrose attracts mainly night-flying moths as the scented flowers open in the evening. Teasel is great for bees and the seeds are eaten by goldfinches. But beware, Teasel self-seeds prolifically but luckily the seedlings are easy to remove when young.