Val Bourne: some bees’ tongues are longer than others – Val explains why
A bee’s tongue determines the flowers it visits, says Val
AS the year wears on it gets harder to identify the bees in the garden. I seem to see a lot of larger bees with tapering abdomens, but I’m unsure whether they’re queen bumblebees or cuckoo bees. The smaller workers all seem to look the same, too. However, looking at the flowers they’re visiting helps, because some bees have shorter tongues than others so they tend to visit flowers with simpler shapes.
At the moment we have lots of honey bees feeding on annual borage (Borago officinalis), which germinated after the summer rains. This coarse-leaved annual has blue starry flowers and these are often floated in drinks, although anything acidic, like a slice of lemon, turns the cornflower-blue flowers pink. Members of the borage family are all nectar-rich and their flowers have the ability to replenish nectar quickly. Comfrey, pulmonaria, brunnera, forget-me-not and echium are also good bee plants.
Honey-bee tongues measure (6.6mm) in length, which is roughly 1∕4in, although they can extend their tongues to 7mm in order to access the smaller late-season flowers of red clover. Early red clover flowers are larger in size and only accessible to bumblebees – an observation made by Charles Darwin in the 19th century.
Having a range of tongue sizes spreads the bees around and helps pollination. When a bee laps up nectar with the spoon-shaped structure at the end of its tongue, pollen sticks to its body. When it visits another flower of the same species, fertilisation takes place and seeds or fruits are produced. Most plants need cross-pollination and that’s why bees are so vital for the human race. Very few plants are self-fertile, so we need bees with furry bodies that transfer pollen as they go.
If a certain bee is only able to visit a limited range of flowers, due to tongue length, fertilisation has more of a chance of happening. There’s also less competition among bees with different tongue lengths, because they visit different flowers and can co-exist without outcompeting each other.
It’s fascinating to watch bees in action. You can see bees unfurling their tongues when they reach the flowers. In most species, the bee’s tongue is guarded by a long two-sided beak of a sheath, which folds under the body when the bee flies. I’ve never been able to see this – so far!
We have a wilding in the garden, a field scabious called Knautia arvensis, and it’s a bumblebee favourite. It’s not a great garden plant because the blue flowers set too much seed, so I rip out handfuls in late summer in a vain attempt to rein it in. This native wildflower grows on limestone verges and it’s a good bumblebee plant in summer, but it’s not visited by honey bees because each flower has a deep corolla tube so honey bees struggle to get any nectar.
Not all bumblebees have long tongues. The abundant and widespread Bombus terrestris, the buff-tailed bumblebee worker, has a tongue measuring 5.8-6.3mm. The huge bufftailed queens are the first to emerge, in early February here, but in warmer cities of southern England the workers are flying throughout winter. They are fond of hellebores and crocuses in spring, and then they visit brambles and hardy geraniums later in the year.
However, buff-tailed bumblebees are adept at robbing nectar and they will bite into the back of long-tubed flowers such as honeysuckle, or into the long spurs of aquilegia. The red-tailed bumblebees also have short tongues, estimated to be 6mm. The early bumblebee (Bombus pratorum) is another robber of nectar that bites into flowers it cannot reach with its 6.4mm tongue.
The longest tongues belong to the garden bumblebee (Bombus hortorum) at 12mm or roughly 1∕2in. The workers visit foxgloves, flying from flower to flower with their tongues extended. They also like red clover, cowslips, vetches and lavender.
“Not all bumblebees have long tongues”