The common carder bee (Bombus pascuorum) is one of the most common bumble bees in the UK. Credit: Dr Thomas Timberlake.
Against the general backdrop of declining insect populations in the UK over recent decades, pollinators such as bees are showing variable, and often alarming, trends in their numbers. Here, Dr Thomas Timberlake, a senior research associate at the University of Bristol, highlights his work which has led to the novel theory that Britain’s gardens could provide a huge boon to UK bee numbers during periods when farmland plants are producing less food.
ScienceVega: Can you give me an overview of bee populations in the recent past?
TT: There is a thing called the windscreen phenomenon when car windscreens, in the 1970s and 80s, would be covered in insects after driving, particularly at night. Today that doesn’t really happen. A realisation of that was one of the first things that got people thinking about how different things had become, that it was a really good ‘canary in the coal mine’ of what was happening.
Essentially what has been going on started as far back as the post-war era of 1950s when there was a desperate push for food and that the UK really needed to grow more. We needed to be more self- sufficient and the message went out to farmers; rip out your hedges and broaden your fields – start using pesticides and fertilisers. It was also going on in a lot of other parts of the world as well. This ‘green revolution’ was really intensifying farming.
What that did in removing all the hedgerows and getting rid of every little patch of bare ground with weeds or flowers, was it removed all of the food that was out there for pollinators.
A study from a few years ago showed that the total amount of nectar in the UK has dramatically fallen by around 30%, which means there is much less food for pollinators and that then cascades down onto pollinators and you can’t have as many bees if there’s not the same amount of food. Nesting sites have been removed and we have also seen an increase in pesticide usage. All of that has meant we have seen a roughly 25% decline in bee numbers across the UK from the 1980s onwards.
There has been a bit of a recovery, or rather a slowdown in the decline, because farmers and governments have noticed something is happening and that because the pollinators have declined so much, it’s actually starting to affect crop yield. That has led to efforts to reverse that: the agri-environment schemes – wider field margins with hedgerows being promoted. We have started to see a little bit of a return, a little bit of an increase in the amount of food, the amount of nectar, in the countryside. It shows a slowdown in the decline but it’s still not great.
Another perhaps more serious issue happening is that the number of different types of flying insects is also declining. In the UK all of the rarer and more specialist bees have declined faster and a lot have gone extinct locally. At the same time a few more common insects have actually become more abundant and that is masking the overall effect of what is happening. We have a decline in the overall numbers, but an even greater decline in the number of different types of bees and other insects.
The buff-tailed bumblebee (Bombus terrestris) is a frequent visitor to UK gardens. Image © Dr Thomas Timberlake.
ScienceVega: Can you give examples of the different fortunes of pollinators?
TT: The bumblebees are perhaps the best known group and within that there is the buff-tailed bumblebee, which is what you are most likely to see flying around your garden. That is doing really well and is therefore one of the rare ‘winners’ of the big shift; it’s actually become more common. At the other end of the spectrum you have the shrill carder bee, another type of bumblebee, and that is doing really badly.
A lot of the bumblebees and butterflies that live in higher altitude areas, such as our hills and mountains, are doing really badly and that is the case with this one. The central rule is the more specialist a pollinator is, the worse it has done. If it lives in a particularly niche kind of habitat, or it can only feed on a few different types of plants, those types of bees have done much worse than the ones like the buff-tailed bumblebee which will eat almost anything and can survive in a lot of places.
A final point to make is that a lot of the time people confuse what’s going on with honeybees with what is happening with wild bees. They are two quite different things. The honeybee is to the bee world what the chicken is to the bird world; in this country they’re mostly domesticated, not wild. Their populations are more driven by the number of beekeepers or the diseases that are going around beehives and not, for example, by declines in habitat availability. It is the wild bees that we need to be really worried about.
The shrill carder bee (Bombus sylvarum) lives in higher altitudes and numbers are suffering greatly in the UK. Credit: Ivar Leidus, CC BY-SA 4.0. <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons.
ScienceVega: Are there bees that have gone extinct globally, or are we talking about bees that have been lost to the UK?
TT: It’s both. There are some bumblebees that have gone completely from the UK; they have literally disappeared as a result of the intensification of farming. There are also some that have become completely extinct globally. But on a side note, one interesting thing happening because of climate change is we are now seeing a lot of new insects that are arriving in Britain for the first time on our southern shores, which is quite exciting.
ScienceVega: How is it that the specialist hill- and mountain-habitat bees that are the faring worst when those habitats are probably the least impacted by the intensification of farming?
TT: That’s a good point and there are a couple of reasons for that. Firstly there are a few specialist species which live in higher altitude areas like the Lake District and the Cairngorms, and they have been affected by a couple of things, the big one being climate change. The reason they live in those mountains is because they are more cold-adapted, they’re specialised on plants that are also cold- adapted. With climate change the temperatures on those mountains is going up and up, leaving no space for them, and it’s not like they can move to another mountain because there’s nothing else nearby. That is a big problem.
The other thing is although our mountains have not been farmed in the conventional way we might think of, they are still very human modified landscapes. If we consider burning grouse moors and heavy sheep grazing, these are things that are reducing the number of flowers and so the amount of food that is available up in those mountains.
ScienceVega: Pollinators are busiest in early spring and late summer; does this typically coincide with flowering seasons on farms?
TT: If we look at the bumblebees, the queens come out of hibernation in February or March, they are really hungry and they need to find food to start setting up their new nests for that year. They are very busy very quickly, then once they’ve found enough food and built up some reserves, they’ll set up a nest and start laying eggs, which is where the colony comes from.
But the problem on farmland is that we have got rid of so many of those early flowering species such as willows and dandelions, and a lot of hedgerow trees, shrubs and flowers that are missing now because everything has become much more homogenised and simple. When the bee comes out of hibernation, they find there isn’t really that much food to go around. But on farmland in later spring there is often a surge in the amount of food available as a lot of things flower all at once, such as big fields of oil seed rape. The natural habitat provides little patches of different flowers, but on farmland they are huge blocks of the same thing.
Ideally you would want lots of different things to balance everything out and provide a nice continuous supply of food. The research we have been doing has shown that gardens really do provide that. They are unusual in that they have so many different things flowering because gardeners love to plant loads of different species, and every garden is different. Together those different plants and those different gardens create a really nice
continuous supply of food through the year rather than the ‘boom and bust’ of farmland. That is much more useful to pollinators; they don’t just need food for a very short period of time and then nothing else, they need that consistency through the year. It seems to be that gardens are playing this amazing role in buffering that kind of boom and bust and having little parcels of food scattered throughout the countryside.
Fields of oil seed rape may provide plenty of food for pollinators, but their flowering season is short. Credit: Daniel Schwen, CC BY-SA 2.5 <https://creativecommons.org/licenses/by-sa/2.5>, via Wikimedia Commons.
ScienceVega: How can gardeners maximise their offering to pollinators?
TT: The best thing about gardens is the diversity of flowers and things flowering throughout the year rather than just in short periods. So try and make sure in your garden that there’s something flowering at every different point in the year from early spring right through to the end of the normal flight season in October. Instead of one big border full of a single flower, try to have a scattering of different things. Perhaps you can have a little flowering shrub in the early spring, then maybe a willow, and leave some dandelions in your lawn. You then have that sequence of different things that come out at different times of year that collectively give insects a nice breadth of options available to them.
ScienceVega: What impact are initiatives such as wild flower borders at the edge of farm fields having?
TT: That is another interesting and somewhat controversial thing because a huge amount of government money has been spent on these agri-environment schemes. Farmers have been paid a certain amount of money to set aside these field margins to support pollinators and other insects. They are useful, but they definitely haven’t been designed as well as they could have been. I don’t want to sound too critical, but just like a field of oil seed rape, often these margins are filled with a couple of different species that might produce loads of flowers, but if those flowers all flower at the same time at a period of the year when there’s already lots of flowers around, which is what they normally do, then they’re not actually helping pollinators because that is not when they need that food the most.
What some of our work has shown is that we might think of urban areas as worse habitats, but actually little patches of gardens can be so much more valuable to pollinators than those field margins. There might be some other better ways than just paying for field margins by perhaps changing it so that farmers have to have a range of different things flowering throughout the year. It might be controversial, but as those little gardens are worth more than a typical field perhaps we should look a bit broader and actually incentivise gardeners to make sure their garden is really beneficial for pollinators?
The UK has this amazing little scattering of gardens. And from the mapping we did for this project, if you are a pollinator and you can fly a kilometre, which is most of the bigger pollinators, then across 90% of the UK they are in range of a garden. It’s amazing that those little gardens could almost be enough to keep things going if they’re really well managed. It is really good that farmers are being incentivised to do positive things for biodiversity, but a lot of researchers are working on how to improve outcomes because the current schemes haven’t been as effective as hoped.
Early spring flowers, Credit: Dr Thomas Timberlake
ScienceVega: Are farmers typically just not ploughing the edges of their fields, or are they actively planting flowers at the edges of their fields?
TT: It differs. A lot of these things are not well policed, but as an absolute minimum the farm margin must not be ploughed. I have done lots of surveys on farms and often we are talking about a tiny strip, perhaps a metre wide, between hedge and field which is not ploughed. At the same time it probably gets all the run-off of the fertiliser from the fields, perhaps with a lot of pesticide residue in it, and it is often just home to grasses and a few weedy flowers. That’s not very good; it’s not going to do anything for pollinators.
In fact, some studies have shown that because you get a huge build-up of pesticides in these margins running off the field, that can actually be a negative because they can accumulate pesticides in the plant. At their worst, they’re really not effective. But there are some much better ones, perhaps five metres wide and actually planted with a seed mix, although they are expensive for the farmers with a lot of land sacrificed.
The point we make in the paper is that gardens are tiny little areas of land, and the density of flowers you can get into a little garden, which doesn’t need to be paid for by the taxpayer and there are ways to incentivise it, is potentially a better way of creating little food islands throughout the landscape.
ScienceVega: What research would you like to do following on from this study?
TT: One theory I have been thinking about for a while is the fact that one of the big things that stops pollinators thriving and bouncing back is that although we’re increasing the number of flowers in the country, we haven’t been doing it at the right times. We still have hunger gaps, bottlenecks, at certain times of the year. I would love to try to fill those gaps by planting on farms to see whether pollinators respond and that that removes those bottlenecks and they can increase their populations.
If we could do that we could suggest to farmers or to policymakers the very best things in terms of investment that you could plant or farm so we are not wasting taxpayers’ money and we’re not wasting land, but we are getting the best value out of it.
