Scottish Expert Beemaster Ann Chilcott considers invasive species in Britain and their link to pollinators.

Relax and read on if you will, I’m not going to be discussing beings from a far-off planet. Rather, species, on this planet, arriving in Britain from other countries under their own steam, or via animal and plant collectors, and settling very easily to proliferate in their new environments. Too easily in most cases, and many of these plants and animals have out-competed native species whilst ousting some from existence.

The Victorians were unremitting in their propensity to conquer the natural world as they did with the foreign lands of the British empire. However, they can hardly be held totally responsible and blameworthy. During the previous century, Carl Linnaeus, the deeply religious Swedish botanist responsible for creating the binomial system of species classification in use today, believed that humans had a divine mission to both take care of the world and to exploit it for their own benefit.

Captain James Cook’s voyages of discovery in the 18th century not only brought home information on new lands to colonise but returned with plants and animals completely unknown till then. Some of these were useful to the economy such as potatoes from South America and later, the tremendously successful tea trade between British India and Britain. Botanist Joseph Banks accompanied Cook to Tahiti and Australia discovering and collecting many plants for the Royal Botanic Gardens Kew and giving his name to some found in Australia. Later, Banks was to become president of The Royal Society in London, a scientific role he maintained for forty years whilst continuing to encourage plant collection and botanical studies.

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Skunk cabbage

The scene was thus set for continued collecting and the 19th century Victorians were keen to enhance the gardens of their stately homes and outdo each other in displays of colourful horticultural extravaganzas.

An example of a plant now commonplace in Scotland is the rhododendron which was brought back from the Himalayas by the Victorians. It escaped and flourished to paint the landscape pale purple and become a nuisance and so it is now illegal to plant or propagate it in the wild. Fortunately, Rhododendron ponticum is not an attractive nectar source to British honey bees because it contains a toxin called grayanotoxin which will harm humans and honey bees in Britain. Bumble bees are unharmed here as are honey bees in Turkey where the honey produced is known as “mad honey” and much sought after by thrill seekers and those interested in alternative medicines.

Looking more seriously now at invasive non-native species it helps to understand what they are and why they are such a threat to our British wildlife. They are species that are introduced to areas outside their normal ranges. The group includes birds, mammals, reptiles, amphibians, fish, invertebrates, viruses and insects. The problem is that those surviving species do so with such vigour that they take over the habitats and feeding grounds of the natives.

There are estimated to be around 2,000 established non-native species in Britain and the cost to the government is about £1.7 billion annually. These species are so adaptable and strong that they have compromised and displaced some of our natives. Interestingly, there have been introductions to the UK from every continent of the world apart from Antarctica.

A good example of a bad outcome is the North American mink which escaped from UK fur farms and has proceeded to decimate our water voles, moorhens, kingfishers, ducklings amongst many other victims.

After habitat loss, invasive non-native species are thought to be the biggest global threat to biodiversity so are taken seriously by our government, and the Non-Native Species Secretariat (NNSS) was established to tackle the threats. To this end a hit list was drawn up by the NNSS in 2016 under European Union (EU) regulations. It comprises 37 species which can be viewed at nonnativespecies.org .Of course it remains to be seen what happens after Britain leaves the EU.

On this list are 14 plants and 23 animals including racoon, Asian hornet, Siberian chipmunk, muntjac deer, ruddy duck, signal crayfish, water hyacinth, water primrose and skunk cabbage. This means that it is illegal to import any of the listed species or grow, breed or sell them, in an effort to limit damage to our native species. They must also not be released into the environment without a permit. Incidentally, the rather attractive skunk cabbage is prolific in Scotland where it thrives in damp environments.

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Himalayan balsam on the banks of the River Nairn, Scotland. Photo: Tom Seeley

The Himalayan balsam, Impatiens glandulifera, has an important relationship with pollinators, especially honey bees for some of whom this plant might just be essential. Himalayan balsam is a well-established non-native plant that was brought back from India in 1839 by Dr John Forbes Royle, a keen botanist born in India and educated in Scotland. He gave his specimens to The Royal Botanic Gardens at Kew, where it was first grown in Britain and from where it escaped. It rapidly spread reaching Middlesex in 1855, and by 1892 it was established in the north of England. From there it spread to Scotland and can be found today over large parts of Great Britain, Ireland, mainland Europe, the United States of America and Canada.

Himalayan balsam was advertised as a great plant for ordinary gardens because of its ability to proliferate in the British climate. A packet of seeds was affordable by most gardeners and they could then compete with the wealthy orchid owners for a colourful and unusual garden. The landed gentry liked it too so it was a popular new plant.

The common names, policeman’s helmet, bobby tops, copper tops and gnome’s hat originate from the hat-shaped appearance of the flower, and bee’s bums from the fact that bumble bees disappear far into the flower leaving only the ends of their abdomens visible. It is also known as poor-man’s orchid and stinky pops.

The Latin name Impatiens means impatient and refers to the way that the seeds are instantly fired out of the flower up to seven metres when contact is made with the seed capsule. Each plant can produce around 2,500 seeds annually.

Having the reputation of being the tallest annual plant in Europe and growing higher than 250 cm, Himalayan balsam favours riparian situations which means that it spreads quickly in the waterways. The greatest damage caused appears to be erosion of river banks when the plants die back at the end of the season leaving bare soil to be washed away by rain. Waterways can get clogged causing flooding.

However, the greatest controversy relates to pollination. It has been posited by some scientists that the very high nectar production and sugar concentration attracts pollinators away from native plants. Scientist, Rinke Vinkenoog (1) conducted research and discovered that most bumble bees actually preferred native plants like common knapweed and bird’s foot trefoil. Hoverflies also preferred other food sources but honey bees were strongly attracted to Himalayan balsam at an important time when they needed to build up honey stores in order to get through the winter successfully.

My own bees visit the River Nairn for Himalayan balsam nectar and pollen from August till October. I know this because of the tell-tale white sheen that they sport on their return, and from the pale off-white pollen on their back legs.

So, what would happen if Himalayan balsam were not here at all? Would our bees be able to find other good sources of nectar at this crucial time of year when other floral sources are diminishing?

Clearly more research is needed.

Reference (1) Vinkenoog, R. 2017, Himalayan Balsam-the impact of an invasive species on the plant-pollinator network, ISBN: 978-1-904379-31-7, The Central Association of Beekeepers, Essex.