The importance of insects

Insects and other invertebrates dominate virtually every ecosystem in the world. They represent about 80% of Earth’s biodiversity, and insects alone comprise over a million species. But this figure is just for the described species: their total number has been estimated to lie between 3 million and as many as 80 million. Scotland is the home to at least 24,000 invertebrate species, more than 12 times the number of all UK bird, mammal and vascular plant species combined.  By Athayde Tonhasca (Scottish Natural Heritage).

Pauline Smith image 1

Invertebrates form the basis of most food chains, and play vital roles in ecological processes which humans depend on such as seed dispersal and pest control. They are the engineers of soil ecosystems, enhancing microbial activity, decomposition and nutrient cycling. As most, if not all, terrestrial organisms depend directly or indirectly on biological processes in the soil, soil invertebrates are keystone organisms, underpinning life on Earth: without them the world’s ecosystems could collapse. These ecosystem services are estimated to be worth billions of pounds to the global economy each year.

Pollination alone is a crucial ecological service; most flowering plants depend on animal pollination for reproduction, and the productivity and quality of around 75% of the world’s main food crops are increased by animal pollination. Additionally, animal-pollinated crops contribute with vital nutrients, vitamins and minerals, and their shortage would aggravate the worldwide ‘hidden hunger’ of micro-nutrient deficiency that afflicts two billion people worldwide. The economic benefit of this ecological service has been estimated to be £132 billion annually, or 9.5% of the world agricultural production value. In Scotland, pollination by insects (mostly bees and flies) has a market value of about £43 million, or around 5% of the value of all crops.

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A number of studies indicate that some insect populations have been decreasing since the late 20th century. These declines are a warning of possible impacts of insect losses on biodiversity and ecological services, but we simply don’t know enough about the overwhelmingly majority of insects. For the species and groups for which declines have been demonstrated, habitat loss and fragmentation, land conversion, agricultural intensification, landscape homogenisation, urbanization, pesticides and pollution are considered the main causes. It is not possible to quantify or rank these factors because every species is affected in different ways and at different degrees; some species adapt to disturbance, others do not.

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Climate change has increasingly becoming one of the greatest threats to the planet’s biodiversity. Models predict that UK species will respond to global warming by migrating northwards at a regional level and upwards at a local level to keep up within their temperature tolerance ranges. Indeed, Scottish species in upland and boreal habitats have become rare or extinct elsewhere in the UK or Europe.

Climate change may have significant indirect effects: seasonal life cycles (phenology) of many plants, herbivores, predators and pollinators are synchronised; changes in temperature and humidity patterns can disrupt these interactions, leading to segregation between plants and their pollinators. However, our understanding of the processes involved is poor and therefore the magnitude of climate-induced effects cannot currently be predicted.

What should we do to protect insects and other invertebrates?

  • The greatest obstacle to insect conservation is the scarcity of basic information about species taxonomy, biology and ecology; millions of insect species remain undiscovered and undescribed, and the abundance and distribution of identified species are mostly unknown. We need to support and encourage efforts to close these gaps.


  • We need to boost the public awareness and profile of insects; except for charismatic (e.g., butterflies), commercially important (honey bees), or medically-relevant (mosquitoes), invertebrates are not always viewed as important.


  • We need to promote the conservation of semi-natural habitats, reduce pollution, and prevent the spread of invasive species.


  • We need to expand integrated pest management (IPM) practices to reduce pests to economically and ecologically sustainable levels.

However, much more is needed to protect “the little things that run the world“.

All images courtesy and copyright of Pauline Smith

Text by Athayde Tonhasca (Scottish Natural Heritage)


Wildflower hub at granton:hub

Making use of derelict land for nature always grabs our attention. And when it includes a wildflower nursery, we’re extra intrigued. That led us to visit Granton:hub, a volunteer-run community arts charity and garden based at historic Madelvic house in north Edinburgh. The work they’ve achieved in creating an open and inviting social space in a built-up area to include a community garden, scrap-store and event space is a huge achievement, creating an excellent area for pollinators as well as people.

Now, the outdoor space of Granton:hub is developing as a raised-bed community garden. Previously concreted, the raised beds are a great solution to growing on sites with thin soil depth. The garden is open to everyone throughout the week, with a gardening drop-in session every Wednesday between 10am and 1pm, encouraging people to get hands on and gain confidence in gardening.

Recognising the importance of pollinators to the success of fruit, vegetables and plant growth, there is a wildflower nursery located within the community garden. Volunteers help grow native wildflowers from locally sourced seeds or seeds purchased from Scotiaseeds. This not only teaches volunteers about the different species pollinators prefer and their growing conditions, but plug plants can be bought, helping to encourage more pollinator-friendly habitat creation across the city.

Leonie Alexander, a volunteer of Granton Hub who also works for Royal Botanical Gardens as their Urban Biodiversity Project Officer talked about the importance of manging expectations when encouraging others to create wildflower meadows. You can never predict or guarantee what will flourish, and you never know what might come up in year three or four that hasn’t flourished before then. That’s one of the interesting and exciting things about growing wildflowers – the result can be a surprise!

Although aspects of what will flourish are left to nature, what you can control is how you prepare the site for wildflowers and how you manage it. The nutrient-levels, depth and type of soil all influence successful establishment. Wildflowers flourish on low-fertility soil, which can make degraded brownfield sites perfect for wildflower establishment. If managed sympathetically, your wildflower site can have ample benefits in offering food and shelter for a range of pollinators and other wildlife.


If establishing a wildflower patch or meadow, wildflower plug plants are good alternatives to growing from seed. They can be planted straight into existing or new grassland areas, bare ground, under trees, in glades etc., and have greater chances of successful establishment. Granton:Hub sell their wildflower plug plants, and can grow to order if requested.

For more information on the great work Granton Hub are up to and how to get involved yourself, visit:


Finding dead bumblebees

The sight of large numbers of dead or dying bumblebees on the ground may be alarming, but the phenomenon is fairly common and usually not related to human actions, and as Athayde Tonhasca reveals, there are several natural causes of bumblebee mass mortality.

Garden Bumblebee, bombus horotorumNormal life cycle. Worker bumblebees have relatively short lives — four weeks is the average lifespan. At the end of the season, only the new queens will live to establish new colonies the following year – the rest of the colony dies. Old bumblebees often can be identified by their ragged wings. Additionally, all bees chuck out debris and dead bees from their nest to maintain hygiene, so a cluster of dead bumblebees could mean that there is a nest nearby, even though you may not see it.

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Cold weather. A spell of cold weather after a reasonable warm period may kill bumblebees and other bees as well. Large number of deaths may also happen if the temperature dips suddenly and severely, usually in the early evening, catching bees outside the nest.

Flooding. Many bumblebee species live as small colonies in burrows in the ground, or within walls and banks. If heavy rainfall floods the nest, the bees become waterlogged and may drown or be killed by the cold.

Predation by birds. Several species of birds, great tits in particular, attack bumblebees. Bumblebees killed by birds often have the contents of their abdomen removed, as the birds usually attack the hind end first to remove the bee’s sting.

Parasites. Bumblebees are victims of several viruses, bacteria and other microorganisms that debilitate and often kill their hosts.


Bumble Bee feeding on a Buddleia bush. ©Lorne Gill/SNH

Do lime trees kill bumblebees? Large numbers of dead or dying bumblebee are often found around some species of lime trees (particularly silver lime, Tilia tomentosa), and it has been proposed that natural chemicals in the nectar of these trees are poisonous to bumblebees. However, recent research has failed to detect any harmful components in lime nectar. Seasonality is the most likely explanation for the phenomenon; lime trees produce lots of nectar, but its volume drops considerable towards the end of the flowering season. Bumblebees keep visiting lime trees, as there are few alternatives at that time of the year. But by then bumblebees are reaching the end of their lives, and have less vitality to get going. So they waste a lot of energy for a meagre return, and eventually they become lethargic and die. We don’t fully understand this process, but the starvation hypothesis would explain why honey bees are immune to the lure of lime tree nectar – they have honey stores back at the hive.

What if a bumblebee seems to be too weak to fly? A grounded bumblebee may be sick or old; there is nothing you could do. But it may be just too cold or have run out of energy. In these cases you could pick her up with a piece of paper or card, put her somewhere warmer, and feed her with some sugar dissolved in water (about 1 part sugar, 2 parts water).

Place a few drops of this solution within her reach, but be careful not to wet her or let her drop in the liquid. When she has warmed and fed, she may fly off.

However, this is an emergency measure to try to recover a single lethargic bee; do not leave a supply of sugary water in your garden. The solution contains carbohydrates of poor nutritional value and incubates pathogens, so bees feeding repeatedly on sugar water solution may die.



Creag Meagaidh – thinking big for pollinators

It was around this time of year, back in 1986, that Creag Meagaidh was declared a National Nature Reserve.  Many people will know it as a reserve in which mountain terrain features heavily.  And whilst that’s true, this can at times overshadow the merits of the lower stretches of the reserve where fabulous tracts of woodland are being slowly returned to life. Now there is another feature to enjoy – an easy pollinator trail within easy striking distance of the car park and visitor shelter.


Initially everything seems to be on a big scale at Creag Meagaidh.  Perhaps no surprise on a reserve which stretches to almost 4,000 hectares.

Exposed munro summits, an impressive mountain ridge and gullies that in winter fill with ice and snow are popular features. Even the fauna here can be big. Red deer being a case in point.

Add to the mix golden eagles, leggy mountain hares and dramatic big views and you can see that things are not on an obviously small scale.


Yet pause for a moment and take in what lies beneath your feet, what is flying around, and your opinion can change.

That is the case even on the high tops where arctic-alpine plants find a home, move off the tops and woolly willow and a rich array of woodland flowers vie for your attention. And where there are a range of flowers there are insects.

That’s why reserve manager Rory Richardson was delighted to install a pollinator trail on this popular reserve.  With admirable determination he worked out what features on the reserve were beneficial for our vital pollinating insects and set about installing a trail route that tapped into the low-level paths around the reserve.

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Rory’s commitment to making a home for pollinators here stretches back some time now. “We have been adding hedges on a regular basis at Creag Meagaidh, we have two Hawthorn hedges and a further 400 metres of mixed tree hedging,”  he revealed, and “we also plant around a quarter of an acre of wildflower mix each year.”  The result is a trail that is therefore well suited to explore species and habitat as well as offering advice to take home.

Tempted to go and see for youself ?  You should.

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The all-abilities trail weaves a route alongside fields and beneath trees allowing visitors to absorb information panels which explore the stories here around flowers, nesting sites, verges and margins, trees and hedgerows.

Find out more about Creag Meagaidh National Nature Reserve.


Records on rooftops

Today’s guest blog comes from Apithanny Bourne who recently completed an MSc research project looking at the pollinating insects on green roofs in Edinburgh.  Apithanny is also the Chair of the East Scotland Butterfly Conservation Branch so her insight is particularly welcome.

Garden roof

Green roofing has been popular in many European countries since the 1960’s but has only started to catch on here in the UK relatively recently.

A quick walk up Edinburgh’s Calton Hill reveals the city is something of a hotspot for the trend, with a number of businesses now adorned in greenery. Whilst there are many well-known benefits – including building thermoregulation and water filtration – there has been surprisingly little research into the ecological benefits of green roofing.

Not one Scottish study exists, and those occurring elsewhere in the UK have focused largely on ground dwelling invertebrates and bees. This is worrying, as many conservation charities now promote installation of the structures on the grounds that they support urban wildlife.

To test these claims, I decided to spend last summer on various green roofs around Edinburgh, recording pollinators.

Seven green roof owners agreed to take part in the study and were visited weekly from June through to September. This covered the peak flight periods for Hymenoptera, Lepidoptera and Syrphidae, which were recorded along a 10m transect.

Sedum roof

Seven ground level partner sites were also sampled and represented the closest area of accessible greenspace to each green roof site. I’m pleased to report that green roofs supported a far greater abundance and diversity of pollinators than expected.

No significant difference was detected in pollinator communities between roof and ground level habitat – indicating green roofs to be a worthwhile extension of existing greenspace. Roof area and height were also found to be unimportant – diversity of flowering plants was a far greater predictor of pollinator abundance and diversity.

Tree bumblebee

This is an important finding, suggesting that popular “Sedum carpet” roofs, may not be the best choice for conserving pollinators. A total of 21 species were recorded foraging on rooftops, including many other invertebrates not considered in this study. Seven species of common bumblebee were abundant and records of leafcutter bees (Megachile willughbiella) on one roof were a particular highlight.

Four species of Lepidoptera were spotted on the more florally diverse green roofs – with small tortoiseshell (Aglais urticae) and small white (Pieris rapae) being the most prevalent. To my surprise one green roof also hosted breeding common field grasshoppers (Chorthippus brunneus) and a very curious family of ducks.

Common field grasshopper

Whilst this study had a limited sample size and many confounding variables – it has made a good first attempt to address gaps in the literature. We now know that green roofing in Edinburgh is providing foraging habitat for a diverse community of pollinators. This is even more promising considering that the rooftops were not necessary created with pollinators in mind.

London alone boasts over 26,000 hectares of unused roof space – cities therefore offer considerable potential in providing habitat for declining pollinators, without sacrificing valuable ground level space. As urban populations continue to rise and connection to nature rises on the political agenda, greenspace availability will become even more important. I believe that green roofing can support both people and pollinators, whilst offering exciting opportunities to engage people with nature.

This summer I’ll be venturing back onto rooftops again with an ambitious citizen science project in mind – I can’t wait to see what’s up there.


All images courtesy of Apithanny Bourne