Dear Readers, I was really looking forward to this talk – I’ve learned a bit about pollinators and pollination over the years, but Jeff Ollerton has spent his life researching the relationship between plants and the creatures that pollinate them, so I knew there would be much to ponder, and I wasn’t disappointed. If you want to watch the talk for yourself, you can access it (and all the other LNHS talks) from their website here or from Youtube here.
Ollerton starts out by talking about the sheer variety of insect species that pollinate plants in the UK. Of course, we automatically think about honeybees, but they are actually atypical, being larger than most of the other 270 UK bees species (only bumblebees are larger) and having the most complex social structure. The ‘solitary’ bees are probably the most diverse group of bee pollinators, although we know little about the life cycles of some of them.
Hoverflies (of which there are approximately 270 species too) are also important pollinators. Of the 60 species of butterfly and 80 species of moth, not all visit flowers – Purple Emperors, for example, feed only on honeydew and plant sap, and some moth species don’t have mouthparts at all. The Noctuid moths are important pollinators, however, especially of plants such as bramble, though this aspect is rarely studied because they are nocturnal.
So, why do insects visit flowers? Different groups come for different reasons. Bees come for nectar and pollen: the first is fuel for themselves, the second protein-rich food for their larvae. Wasps and predatory flies may hang around flowers in order to capture other insects. Beetles and some fly species hope to meet their mates on flowers: who can forget the infamous ‘bonking beetles’ who seem to use blossom as their personal speed-dating site?
Some other insects that visit plants are seed-parasites, but some plants, such as the cuckoo-pint, repay the favour by giving visiting insects no reward at all. Insects are drawn in by the warmth the plant generates and its distinct smell of cowdung – once the insects are inside, they are trapped overnight, get completely covered in pollen, and presumably, once released, visit a different plant the following night.
In other countries, a wider range of animals act as pollinators – not just birds and bats, but small rodents, lizards, and even cockroaches. But what makes an effective pollinator? Ollerton had an interesting list of characteristics.
- The size of the pollinator must be appropriate for the flower – too small and it probably won’t pick up the pollen correctly, too large and it will destroy the flower
- It must be hairy (or feathery) enough to pick up the pollen
- It must be abundant enough to transfer the pollen to enough other plants to make reproduction effective
- It must behave properly on the flower – some bees ‘nectar-rob’ for example, biting a hole in the base of a flower to get at the nectar without actually pollinating the flower
- It must behave properly between flowers – i.e. it must regularly visit the right kind of flower. if it chops and changes on a whim, the pollen might end up on the stamen of a completely different species.
- It must not be too keen on cleanliness – this was something I’d never thought about. Honeybees, for example, often groom between flowers, stuffing the pollen into their corbicula (pollen baskets) from where it can’t pollinate any other flowers that the bees visit.
All this means that there are a wide number of criteria that have to be met before effective pollination can take place. And it is extremely important – for one thing, pollination underpins the effective survival of most terrestrial ecosystems, because without plants, there are no animals, and if pollination doesn’t take place, the plants can’t reproduce.
From the point of view of human beings, over 75% of food crops are animal-pollinated, and this produces over 35% of our food overall. Furthermore, crop-pollination has been found to be more effective if there are a variety of pollinators – the famous honeybee only performs about 30% of pollination in the UK, with the remainder being done by wild pollinators.
So, what is the state of wild pollinators? There have been some drastic declines, and there is little doubt that there is at least as much, and probably more, pollinator diversity in suburban and urban gardens than there is in the countryside, largely due to the use of biocides and the destruction of mixed grassland and meadows.
Climate change is also altering the mix of pollinators: bumblebees, which were originally tundra-adapted, are likely to be at risk whilst many of the smaller bees might have an advantage. However, nothing is absolute – the tree bumblebee (Bombus hypnorum) arrived in 2001 and is now moving north and west at a rate of knots. This is the bee that is most likely to make its home in a nest box or (as the name suggests) in a tree, and very handsome it is too.
So, if we want to encourage pollinators in our gardens, what do we need to do? Ollerton has developed a model called the pollinator requirement triangle.
First of all, pollinators require flowers. Some species are specialists – you’ll have noticed this if you ever watch the bees and hoverflies in your garden. In mine, the common carders are especially attracted to the bittersweet (Solanum dulcamara) flowers because they have the technique of buzz-pollination down to a T, while the heavier bumblebees like the foxgloves and penstemons. For this reason it’s important to have a diversity of flowers, and to have a long flowering season. Furthermore, it’s good to plant in drifts so that there’s plenty of the same thing for the pollinators to use – you can watch the bees returning again and again to the lavender in the front garden, for example.
Secondly, pollinators require somewhere to aid their reproduction. This can include host plants for larvae, nesting sites, and sometimes specific microhabitats, such as close-cut turf in a sunny spot for many solitary bees.
Finally, there might be supplementary requirements. Leaf-cutter bees like the leaves of roses or vines, for example, and some carder bees like the woolly leaves of Stachys byzantina. Bumblebee queens need hibernation sites such as mouseholes. The larvae of hoverflies can have a wide range of requirements, including aphids to munch upon. In short, too much tidying up can be a bad thing, which is a great relief to me, scatter-brained gardener that I am.
However, Ollerton’s final comments also give food for thought. A garden should be seen in the context of the area roundabout – a bumblebee can fly for about 2.5 kilometres in search of food. So, what’s in your local area? For me, the presence of remnants of ancient woodland clearly influences the animals that come to the garden – the greater spotted woodpeckers spend most of their time in the wood and pop in to see me when food is short there or when they have youngsters to feed. The same is undoubtedly true of the bats that I sometimes see. What I’ve taken away is the thought that I need to find out more about the pollinators that are in the area naturally so that I can help to support them.
This was a great talk, with much to think about. And I already have an order in for Jeff Ollerton’s new book Pollinators and Pollination. Well worth a read, I think.
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Photo Two By Charles J Sharp – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=31980634