Judicious poisoning

By Athayde Tonhasca

Bright lemon-yellow globeflowers (Trollius europaeus) bring a bit of gaiety and colour to damp and shady areas such as woodlands, river banks, upland pastures and meadows across Scotland, northern England and northern Wales. These globe-shaped flowers are unusual: they have tightly-closed sepals that encase the true petals, which have nectaries at their base. They look like big yellow buds at the top of long stems, and rarely open fully. 

Globeflowers © BerndH, Wikipedia Creative Commons

This type of arrangement does not encourage most pollinators because they have hard times getting to the pollen and nectar. But one group of insects doesn’t mind: the root-maggot flies of the genus Chiastocheta, of which five species have been recorded in the UK. These are anthomyids – from the family Anthomyiidae, a name derived from the Greek anthos (flower) and myia (fly). The less flattering ‘root-maggot flies’ comes from the fact that their larvae grow inside stems or roots of various plants.

A fly investigating a globeflower © Uoaei1, Wikipedia Creative Commons

Male and female flies wiggle their way towards the flower’s nectaries. Once inside, they feed and mate, pollinating the flower in the process. Male and female are hairy, so pollen gets attached all over their bodies. But females need more than food: as true root-maggot flies, they deposit their egg on the carpels (the flower’s seed-bearing structures), and the resulting larvae develop and feed on the seeds. So Chiastocheta spp. are simultaneously pollinators and seed parasites.

A female Chiastocheta setifera © Janet Graham, Wikipedia Creative Commons

Insect pollination is a mutualistic relationship, where each partner benefits from the other: the pollinator gets food or some other reward, while the plant gets fertilized. Another way of seeing it is as reciprocal exploitation: flowers produce as little pollen and nectar as necessary to attract pollinators, and insects would take away as much of those resources as flowers allow. So flowers must maintain a fine equilibrium between attractiveness and the metabolic costs of producing pollen and nectar. In the case of globeflowers, there is the added burden of seeds lost to root-maggot flies.

Seed head of a globeflower: cosy growth chambers for root-maggot flies © Ivar Leidus, Wikipedia Creative Commons

To avoid over-exploitation by Chiastocheta spp., globeflowers resort to chemical defence. Like other species of the buttercup family (Ranunculaceae), globeflowers are slightly poisonous: they produce compounds that discourage plant feeders. One of these chemicals, adonivernith, plays a regulatory role in the pollination/seed parasitism balance. Adonivernith is spread all over the plant, but concentrates in the flowers (it contributes to their bright yellow coloration). If the number of larvae growing inside the flower increases, the amount of adonivernith also increases, eventually inhibiting larval growth and feeding. It’s the globeflower’s way to regulate the loss of valuable seeds for the sake of pollination: when flies become a liability, they are curtailed by intoxication.  

Male flies are also important for maintaining the right balance between pollination and seed predation. They are smaller and transport less pollen than females, but make about twice as many flower visits during the same time period. Male pollination incurs no seed losses, so they help reduce the pressure on their host. 

In nature, it’s often a matter of harmonizing antagonistic interests.   

Utrecht’s new treaty

Perhaps not since 1474, when the Treaty of Utrecht signalled the end of the Anglo-Hanseatic War, has the ancient city of Utrecht been so prominently in the news. I exaggerate of course, but the war on biodiversity loss and climate change has thrust this old university town into the public eye once more. Today bus shelters rather than naval power are amongst the weapons of choice.

In a bold and innovative move to help pollinators Utrecht city council has teamed up with partners to transform over 300 bus stops into ‘bee stops’. This has been achieved by giving the roofs of the adjacent bus shelters a make-over which includes pollinator-friendly sedum planting.

There is a climate change mitigation bonus beyond this as the plants have the capacity to capture fine dust particles and store rainwater.  And we shouldn’t overlook the health and wellbeing angle as the additional greenery in the city makes for a visually more appealing urban view.

Why has Utrecht gone down this route?

The city, the fourth largest in the Netherlands, has declared an intention to deliver a circular economy and is striving to reach a net-zero position as quickly as possible. The buses that call at these bus stops are increasingly electric and by 2028 Utrecht’s administrators predict they will have a ‘clean’ urban transport system.  

Not surprisingly perhaps, the energy for these buses taps into the numerous windmills and turbines that pepper the local landscape.  Even the wildflowers and grasses on the roofs of the city bus shelters are watered by a team using electric vehicles. By using sedums widely in the planting schedule that watering is effectively minimised and supplements the service offered by rain.

Much of the progress here leans heavily on the expertise and drive of the EIS Insect Knowledge Centre. They have monitored the bus stops and made an inventory of 30 of the shelters to see just which insects are making use of this new resource.

The EIS team visited their chosen shelters twice between May and August and counted a total of 8 bee species and 5 hoverfly species. It’s important to bear in mind that a very dry and warm summer will contribute to dry roofs and late blooming of flowers. This, and the fact that the sedum roofs are relatively small, helps account for the smallish numbers (the Netherlands does indeed have around 360 species of bee).

The Utrecht project was born out of seizing the moment. When the local authority realised that 481 of its shelters needed to be renewed they saw a moment of opportunity and elected to cover 316 of them with a sedum roof. It’s a low maintenance solution to tackle issues around potentially damaging rainwater incidents, pollinator pressures and air quality concerns. 

Mind you there was nothing low maintenance about the survey challenges for John Smit and Tjomme Fernhout who often found themselves at the end of a ladder waving a large inset net around to collect samples.

The role of EIS is important to Utrecht’s council in helping to take stock of the success, and challenges, behind bus shelter greening.  Monitoring and research are essential if we acknowledge that not everything succeeds first time.  

Given that the roofs are in an urban setting and that many bees look to feed near their nesting site the smaller than anticipated pollinator numbers is perhaps not such a surprise. It’s also worth bearing in mind that a lack of bloom wasn’t ideal, nor have three consecutively particularly dry spring and summer seasons helped.  However, such problems – which the EIS team picked up – can be tackled in coming years with a little more watering than initially anticipated, and perhaps a wider mix of plants. The council has tweaking the composition of plants on some bus stop rooftops in hand already.

187 km to the north of Utrecht lies the city of Groningen which revels in the strapline ‘Nothing surpasses Groningen’. As far as cycling is concerned that is a fair claim. But the city does much more than encourage that healthy and booming form of transport to adapt to the challenges of climate change. For example, the intriguingly-titled promote green facades is part of their forward-thinking climate policy. The council and major employers have worked hard to make building facades in the city greener. Where walls were once uniformly harsh brick and concrete they are increasingly vibrant green vertical gardens. That’s another step along the road to cleaner air and better flood management systems.

Groningen and Utrecht are all fine urban examples. They fall within a nation where, since 2015, the national government has been committed by law to cutting emissions and ensuring greater climate change mitigation efforts are enshrined in law. Back in 1953 1,835 people died in a catastrophic flood. It’s instilled a belief that prevention is better than tackling any aftermath.

What’s happening in the Netherlands is now gaining momentum in other European cities.

Nature based solutions are a win-win. The introduction of porous pavements, restoration of wetlands, and increasingly greening of our cities not only slows down surface water, it connects people with nature and creates more pleasant urban environments. And for wildlife all of the above is a triumph.  For pollinators in particular Utrecht’s new treaty promises to help address many issues they face.

All images courtesy of Tjomme Fernhout (except the one of him swinging the net)


Find out more about the Utrecht bus shelter project

Find out more about the EIS knowledge centre

Quietly riding off into the sunset

By Athayde Tonhasca

In 2019, four American and Australian enthusiasts set off to Indonesia on a bold mission: to find the Wallace’s giant bee, Megachile pluto. This bee was first described in 1858 by naturalist, explorer and co-author of the theory of evolution Alfred Russel Wallace (1823-1913). After its official discovery, the Wallace’s giant bee – aka the giant mason bee – disappeared from the records and was thought to be extinct until it was rediscovered in 1981. The bee vanished again for the next 37 years, until the 2019 search expedition: the team found and filmed the Wallace’s giant bee. 

A female Wallace’s giant bee and a worker honey bee © Abalg, Wikipedia Creative Commons

Denizens of tropical jungles are expected to be elusive and mysterious, but the Wallace’s giant bee lives up to its name: it is the largest bee on Earth. If a bee of this size can go unnoticed and believed to be extinct for most of its recorded history, it’s not surprising that less spectacular species can go unrecorded for a long time. The bee Pharohylaeus lactiferus, sighted this year in Australia, was previously seen in 1923; the bone skipper fly (Thyreophora cynophila) was first described in 1794, remained undetected until 1850, then disappeared again until its rediscovery in Spain in 2009. There are many other examples of what is known as ‘Lazarus fauna’: species believed to be gone, only to ‘come back from the dead’ when rediscovered.

Extinct… Not. The bee P. lactiferus (© Natural History Museum, Wikipedia Creative Commons) and the fly T. cynophila (© Carles-Tolrá et al. 2011, Boletín de la Sociedad Entomológica Aragonesa 48: 217‒220)

Small size and secretive lives are only partially responsible for the patchy or absent recording of insect species: rarity is a huge factor. 

Rarity is one of the quirks of life on Earth; for almost every ecological community (a group of species living in the same location), most species are represented by few individuals, and most individuals belong to a few common species. Reams of paper and gallons of ink have been spent trying to explain why it is so, with no consensus so far. Whatever the explanation, there are many rare species and only a few common species.

Relative species abundance of beetles sampled from the river Thames © Aedrake09, Wikipedia Creative Commons

Rarity is a big headache for conservationists because for most species it is difficult to say with confidence they are declining or no longer present (i.e., extinct): some of them may just have been overlooked because of low numbers or obscure existences. The International Union for Conservation of Nature (IUCN) considers a species extinct when ‘there is no reasonable doubt that the last individual member has died’. This is a sensible approach, but ‘no reasonable doubt’ is a tall order for insects. So it is not surprising that the IUCN has registered fewer than 50 extinct insect species worldwide, and that the list of 23 American species declared extinct last month by the Fish and Wildlife Service does not include any insects: conservationists just don’t have enough data.

The Wallace’s giant bee may be a naturally rare species, but much of its habitat has been wiped out and replaced by crop fields and palm oil plantations. So it may very well become extinct. But if it does, it will take us many years to know. 

These uncertainties are vexing and underplay the trouble faced by insects. The only way to deal with the problem is by keeping a finger on the pulse of populations to notice signs of decline, and this is done by meticulous, long-term monitoring. Thanks to the work of enthusiastic and determined volunteers, we know that in Britain at least thirty species of larger moths have become 40% less abundant in the last 10 years, on average the distribution of 112 species of solitary bees have contracted between 1980 and 2013, and over 40% of dragonfly species have increased since 1970. As incomplete and tentative as these figures are, they reflect Britain’s long tradition of biological recording. We have only a nebulous idea of what’s happening in most of the world. 

Serendipitous rediscoveries of species thought to be extinct are heart-warming, but they are far and between. Considering the relentless shrinkage of natural habitats across the globe, species vanishings are more likely to be permanent. By monitoring, we can raise the alarm and trigger action. If we don’t monitor, inconspicuous species, the very fabric of biodiversity, may slip quietly into oblivion. 

The Franklin’s bumblebee (Bombus franklini), last seen in the western United States in 2006: perhaps gone forever © Project Noah

Garnock’s Buzzing

In conversation with … Lorna Cole of SRUC, and Gill Smart of the Scottish Wildlife Trust, working together on Garnock’s Buzzing.

Garnock’s Buzzing is one of 28 projects being undertaken by Garnock Connections, a landscape partnership funded by the National Lottery Heritage Fund.  The project will enhance, improve and promote both natural and cultural elements of the area around the River Garnock. As Lorna and Gill explain, great strides have been made for people and pollinators through targeted habitat creation and citizen science in the Garnock Connections study area. 

Why would you say projects like Garnock’s Buzzing are important?

Since the end of the Second World War it is reckoned that we have lost 97% of our wildflower meadows. As a result we are losing the joy of seeing an explosion of colour during the summer months, and leaving some of our most precious bees, and other pollinators short on food and habitat. Through the Garnock’s Buzzing project we aim to do our bit to change this and make the Garnock Connections landscape a haven for pollinators.

What sort of projects have you developed?

Well, where to begin? There have been so many successful elements that the list is quite lengthy. So far, we have actively involved almost 100 school pupils and trialled different cutting regimes to identify pollinator friendly verge management practices.   We’ve also put up around a dozen information signs, created many new meadows, put up 14  bee hotels or bee banks and created 0.9ha of bare earth habitat for mining bees.

The white rectangle to the top right of this image is a wonderful wildflower meadow in Irvine

Where can people go to see these new meadows for themselves?

Meadow areas have been established on both Irvine Beach Park and Stevenston Beach Park, giving large numbers of people access to enjoy the flowers and insects.

Lochshore in Kilbirnie is another large public open space with an area given over to wildflowers. 

Which element are you, Lorna, most pleased about with your Garnock’s Buzzing work?

Garnock’s Buzzing kicked off just about the same time as COVID 19. With the country in lockdown we were no longer able to undertake the visits to schools we had originally planned. To help teachers and pupils alike SRUC developed a wobbly apple experiment to highlight the important role that insects play in pollinating crops. This allowed us not only to engage with children in the Garnock Connections area, but also throughout Scotland.

I’ve seen the stunning meadow near the boating pond at Irvine Beach Park. That’s a fantastic resource for pollinators. Can you tell us a little about how that area was created and how you manage it?

This was collaboration between the Scottish Wildlife Trust and North Ayrshire Council, made possible by Garnock Connections.  In autumn 2020, a tractor was used to lightly plough the ground and mechanically sow a wildflower mix containing both annual and perennial species.  The annuals flowered profusely in summer 2021 and we could see the leaves of future perennials developing.  The trick to keep the flowers blooming is to cut in autumn and remove the clippings while allowing lots of seeds to fall to the ground.  We plan to use some of the clippings, which will still contain plenty of seeds, to start new meadow areas nearby.

If anyone reading this wants to help with Garnock’s Buzzing and get involved in projects, what should they do?

Email Garnock Connections Natural Heritage Officer, Neal Lochrie neal.lochrie@rspb.org.uk or visit their website https://www.garnockconnections.org.uk/

Find out more:

Garnock’s Buzzing is led by SRUC, the Scottish Wildlife Trust and Buglife.

Garnock’s Buzzing


The Green Infrastructure Fund is part of the Scottish Government’s current European Regional Development Fund programme, which runs through to 2023.  This is one of two ERDF Strategic Interventions led by NatureScot – the other is the Natural & Cultural Heritage Fund.

You can follow the European Structural Funds blog for ESF activities, news and updates. For twitter updates go to @scotgovESIF or use the hashtags #ERDF and #europeanstructuralfunds

Hazardous neighbours

By Athayde Tonhasca

Since their discovery in the 1800s, viruses have confounded scientists and philosophers because they raise questions about the very nature of life. Viruses consist of genetic material (DNA or RNA) coated with protein, and that’s about it. They draw a blank on six of the seven fundamental indicators of a living organism: movement, respiration, response to stimuli, feeding, excretion, and growth. They do better on the seventh – reproduction – but to a point. They do multiply, although only by seizing the cell machinery of a host to make copies of themselves. But viruses have one essential asset: genetic heredity, which allows them to evolve. So viruses are considered living or non-living, depending on who you ask. That’s why they have been defined as ‘biological entities’, ‘at the edge of life’, and ‘existing at the border between chemistry and life’. Considering the viral upheaval that hit us in 2019, we could settle for the definition offered by immunologist and writer Peter Medawar (1915-1987): ‘a virus is a piece of bad news wrapped up in protein’ (although you may be surprised to hear that viruses are fundamental to life on Earth). 

Bacteriophages (viruses that infect bacteria) mobbing a bacterium © Graham Beards, Wikipedia Creative Commons

Living or non-living, viruses act as intracellular parasites, and insects certainly are not immune to them. Some viruses are used as biological control agents against agricultural pests and vectors of diseases, but others are harmful to insects that benefit us, such as the European honey bee (Apis mellifera).

Beekeepers have to deal with a number of pests and diseases, including RNA viruses with ominous names such as acute bee paralysis virus, black queen cell virus, Israeli acute paralysis virus and slow bee paralysis virus. Among this disagreeable family, the deformed wing virus (DWV) is particularly damaging to apiaries in Europe and other temperate zones; DWV variants are among the world’s most widely distributed and contagious insect viruses. Infections are generally detected in workers with shortened abdomens and deformed or missing wings.

A honey bee with deformed wings © Shawn Caza, Wikipedia Creative Commons

The virulence (i.e., the capacity for causing disease) of DWV and other viruses is dramatically heightened by another honey bee scourge: the varroa mite (Varroa destructor). This pest transferred – ‘host jumped’ – from the Asian honey bee (Apis cerana) to the European honey bee in the early 1900s, and since then it has caused havoc to the beekeeping industry around the world. The mite depletes bees’ reserves by sucking up their fluids, and it also injects virus particles into its hosts. The synergistic combination of varroa mite and DWV has had a devastating impact on managed honey bees, with sharp increases of overwintering mortality and colony losses.

A honey bee pupa infested with the varroa mite, a vector of DWV. Image in the public domain

Harm to honey bees is bad enough, but DWV can do much worse. It has been found in bumble bees, mason bees, mining bees, wasps and at least one species of ant and one species of beetle. We don’t know how badly DWV affects most of these non-Apis hosts because infections are typically asymptomatic. Hosts’ immune system may suppress viral replication, or the virus may just be picked up accidentally by feeding on pollen or nectar. But some bumble bees are not so lucky: they die or develop wing deformities when infected by DWV. 

Bumble bees are not parasitized by varroa mites, so they get infected by DWV some other way. The most likely route is through feeding; bumble bees pick up the virus when collecting nectar or pollen from a flower that was visited by a diseased insect – probably a honey bee. Direct virus transmission from honey bees to bumble bees has not been demonstrated, but there is plenty of circumstantial evidence to suggest it: honey bees deposit viruses on the flowers they visit, and apparently viruses occur mostly on flowers near apiaries; bumble bee rates of infection are higher when honey bees are present and almost non-existent when honey bees are not around. 

A dangerous encounter: a bumble bee and a honey bee sharing a flower © Uroš Novina, Wikipedia Creative Commons

Putting all the clues together, flower sharing seems to be responsible for honey bee to bumble bee ‘pathogen spillover’, which happens when a pathogen transfers – or ‘spills over’ – from a reservoir species to another receptive species. There is much to be discovered about bee viruses and hosts’ responses, but what we know suggests we should keep honey bees apart from bumble bees and other pollinators, especially when rare or endangered species are involved. That’s one of the reasons why some countries such as Australia and the United States restrict beekeeping in national parks and other conservation areas.  

Honey bees are incredibly important and valuable: but they can also be a health hazard to fellow pollinators. Awareness of this risk can help us manage bee hives and pollinators’ habitats, for example by planting more flowers throughout the growing season so that the likelihood of spillover is reduced. Which is good for honey bees, for wild pollinators, and for us.

The apple bumble bee

Given the popularity of apples in Britain you could be forgiven for expecting the apple bumble bee (Bombus pomorum) to be one of the species found here. However, think again. The Bumblebee Conservation Trust’s website records sightings on the south coast in the mid-1800s, whilst the equally highly-reputable NBN Atlas, which holds more than 198 million UK species records, has only two mentions for the apple bumble bee. They are both historic sightings.

The apple bumble bee (Bombus pomorum) © Picto Sauvignet louis didier, Wikipedia Creative Commons

Dave Goulson’s highly regarded and hugely enjoyable ‘A Sting in the Tale’ makes reference to the apple bumble bee as maybe having never been resident in the UK. The four specimens known were, he explains, found on the dunes near Deal (Kent) in 1865. And whilst he reckons the sightings likely to be genuine, given the stature of the recorder and the existence of specimens, no further records have been confirmed in the 150 plus years since.

We can surmise with some confidence that this isn’t down to under-recording. Given the long-standing and very efficient history of studying bumble bees on these shores it would hardly be missed. As things stand you need to visit central and eastern Europe to catch a glimpse.

In 1999 Lithuania marked several important events on postage stamps. The 400th anniversary of the printing of the first book in the Baltic state was one, two bumble bees which featured on their red list – one being the apple bumble bee – were also of sufficient national interest to feature. 

Bombus pomorum has seen its range alter on the continent. It hasn’t been recorded in Denmark, Spain, or Belgium in recent years. Unlikely to be found near the coast, it is fond of flowers such as thistles, and as agriculture continues to intensify, and so-called weeds are marginalised, it is now viewed as being in an unfavourable or vulnerable condition within its current range.  Additionally, the species is considered to be at risk due to the threat of climate change.

That said there was interesting news recently when two specimens were collected in Siberia.  This was a first for this species, although it could be that rather than expanding its range it had simply gone unnoticed previously.

Apple blossom in the Battleby orchard. ©Lorne Gill/SNH.

We can’t always take a species name as definitive or too literally. Why was the apple bumble bee so named?  That may be lost in time. Sometimes even well known names can be plain misleading, rather like the Koala Bear (which isn’t a bear) or, stepping beyond nature, the Hundred Years War (which lasted 116 years). In the case of the apple bumblebee the name almost suggests it specialises exclusively on apple blossom, which is unlikely given the very limited flowering period.

On Steven Falk’s splendid Flickr Album (a hugely informative and enjoyable resource) he has images of Bombus pomorum and says this: “Only ever known in Britain from Deal Sandhills and adjacent Kingsdown area (three males thought to date from 1857 and a queen from 1864). Considered by some to be a windblown vagrant or temporary colonist rather than a permanent resident, though the Kent population might also have represented a relic population from the pre-agricultural revolution landscape.”

It is estimated that we import around 476,000 tonnes of apples, a figure perhaps made higher than expected because of an apparent 36% decline in the number or orchards here since the mid-1980s. But as a fruit that can be easy to store, is a key element of many ciders, and in a nation where apple pies and apple crumbles are popular winter-warmers, their popularity shows no signs of waning.

In our own apple industry names such as Cox, Smith and Bramley are indelibly linked to our appreciation of apples. The Bramley apple alone, for example, is produced in impressively huge numbers (reckoned in some quarters to be around 83,000 tonnes each year).

There have been many studies looking at how apples are pollinated. All agree that insect pollination is key to apple production, but there is still some way to go in identifying the most successful pollinator of this fruit.  

There are a variety of reasons for scientists being cautious in making sweeping statements. Apples are many and varied. Firstly, there is a widely acknowledged varying nectar and pollen availability between different apple blossom varieties, thus making them more or less attractive to particular species. Secondly the four main guilds of apple pollinators – bumble bees, honey bee, solitary bees, and hoverflies – have different feeding specialisms so will have certain preferences. Thirdly, apples flower at a time when the weather is hugely variable, so the range of species visiting is likely to vary considerably between years.

Science will undoubtedly unravel the mysteries. 150 years on from those sightings in Kent scientists continue to discover more about species. Research examining pollen preserved on the hairs of Natural History Museum specimens has made it possible to gain a better insight on many species’ foraging preferences.

What isn’t in dispute is the major contribution made by a range of insects, especially bees, to apple production, even if we don’t have the services of the apple bumble bee on our shores. When you next bite into an apple remember to thank our insect pollinators.

Fig wasps, evolutionary marvels

By Athayde Tonhasca

When people talk about keystone and indicator species, often what they mean is ‘my favourite species’, or ‘the important species I work with’. But one group of organisms truly deserves the label of keystone species: figs. The genus Ficus comprises over 900 species spread throughout the tropical and subtropical regions as shrubs, lianas (woody vines), or trees. Strangler trees – which don’t strangle anything – are one of the best known types of fig plants.

Many fig species produce fruit asynchronously throughout the year, so many animals have a steady supply of abundant and nutritious food. This is especially important during the dry season, when most plants do not fruit. Figs are often preferred even when other fruits are available because they are rich in calcium, a mineral usually in short supply. So figs are essential for a wide range of birds and mammals such as pigeons, toucans, parrots, macaws, bats, peccaries and monkeys. Over 1,200 vertebrate species feed on figs.

The strangler fig Ficus aurea © Forest Starr and Kim Starr, Wikipedia Creative Commons, and the diversity of fig characteristics © Lomáscolo et al. 2010. PNAS 107(33):14668-72

Figs support the diversity and functioning of ecosystems around the world, but they can only do that thanks to some tiny wasps.

Chalcid wasps are an enormous group of insects, estimated to contain over 500,000 species. Most of them are parasitoids of other insects, but a small group belonging to the family Agaonidae has one purpose in life: to get into a fig to reproduce. By engaging in fruit breaking and entering, these wasps, appropriately known as fig wasps, pollinate the fig plant. 

A female fig wasp © Robertawasp, Wikipedia Creative Commons

The mission is made immensely complicated by figs’ morphology. Botanically speaking, a fig is not a fruit but a type of inflorescence known as a syconium (from the Ancient Greek sykon, meaning ‘fig’, which originated ‘sycophant’, or ‘someone who shows a fig’; a term of curious etymology). A syconium is a fleshy, hollow receptacle containing simplified flowers or florets, and each floret will produce a fruit with seeds in it. A fig harbours dozens to thousands of florets and fruits, depending of the species. The crunchy bits of the fig we eat are not seeds but fruits.

Florets need pollination, not an easy proposition when they are bunched up and locked inside a container. So the fig wasp’s first hurdle is to get inside the fig. A female wasp does it through a hole at the bottom of the fig (the ostiole), which loosens when the fig is ready for pollination. 

Longitudinal section of a syconium. The inner wall of the hollow chamber is covered with florets, and the ostiole at the bottom is the door for female wasps © Gubin Olexander, Wikipedia Creative Commons

A receptive fig does not make life much easier for the female wasp. She has to chew her way through, pushing and squeezing, often having her wings and antennae snapped off in the process. She will find a floret, insert her long ovipositor into it and lay an egg. As she’s busy doing that, pollen grains attached to her body get rubbed off onto nearby florets, assuring their pollination. With the job done, the female wasp dies.

The ovules of florets that receive eggs will form galls in which the wasp larvae develop, while pollinated ovules turn into fruit. The adults chew their way out of the galls, males first. Sometimes they help females get out from their own florets and mate with them. Males will then chew a hole through the fig wall to let the females escape. Males stay behind: they couldn’t go anywhere, as they have no eyes and no wings. After an ephemeral life spent entirely inside a fig and marked by moments of glory such as fertilising females and setting them free, males die. 

A male (L) and a female fig wasp recently emerged from their galls. The male is using his mandibles to open a gall containing a female to let her escape and be the first to mate with her © van Noort et al. 2013. African Invertebrates 54(2): 381-400

A female collects pollen grains from intact florets or picks them up by accident before braving the world outside. She will follow the trail of chemicals released by a host plant to find another fig receptive to pollination and start the cycle again. But she must be quick: she has a few hours to three days to live, depending on the species. And to complicate things, not any fig will do. Each species of fig tree is pollinated by one or a few host-specific fig wasps, which is an outstanding case of coevolution

The great majority of female wasps don’t make it, but a few do: they catch rides on wind currents above the canopy to find host plants over 10 km away, farther than most pollinators. This is a remarkable achievement for such small, fragile, and short-lived insects. 

You can learn much more about figs and fig wasps at Figweb from Iziko Museums of South Africa.

Perhaps nothing exemplifies better the wonders of fig pollination than the exploits of Ceratosolen arabicus in Namibia. This wasp pollinates the African fig tree (Ficus sycomorus) along the Ugab river in the North Namib desert. This is one of the most inhospitable and remote corners of the planet, famous for its Skeleton Coast, a place of shipwrecks and marooned sailors. African fig trees occur in isolated clumps along the riverbank, but that’s not a barrier for the wasp: it covers average distances of near 90 km and a maximum of 160 km over the desert at night in search of a receptive fig. As the wasp survives for 48 h or less, this quest must be quick and efficient.

Dry Ugab riverbed, Namibia © Theseus, Wikipedia Creative Commons

How do figs and fig wasps relate to us, denizens of fig-less countries? This pollination system has a profound influence on global biodiversity and ecosystem functioning, so it affects us as well, even if indirectly. The story of figs and wasps also illustrates the capabilities, drive and hardiness of minute, easily overlooked insects that are so important for us and nature.

Lights-out, please

By Athayde Tonhasca

As the human population increases and concentrates more and more in cities, the world becomes more illuminated. Artificial light at night (ALAN) is an ever growing phenomenon because of the lighting of streets, parking lots, roads, buildings, parks, monuments, airports, stadiums – basically any manmade structure. This artificial light is scattered into the atmosphere and reflected back, particularly by clouds, creating a night-time sky luminance known as ‘sky glow’. Excessive illumination and artificial sky glow spread way beyond urbanized areas, essentially contaminating the whole landscape with light: night-time darkness is disappearing.

Sky glow over Kent © Chris Isherwood, Wikipedia Creative Commons

The Milky Way galaxy has awed civilizations and inspired many philosophical thoughts about mankind’s insignificance, our place in the big scheme of things, the fleeting nature of life, and what it’s all about. But if young Europeans or Americans are asked to share their impressions about the Milky Way, chances are the responses will be limited to a shrug or a puzzled look: the Milky Way is hidden from about 60% of Europeans and 80% of North Americans because of light pollution. When Los Angeles went through a blackout in 1994 because of an earthquake, emergency services received several calls from nervous citizens about a giant, strange, silvery cloud in the dark sky. These Angelinos were seeing the Milky Way for the first time.

The Milky Way, unseen by many © Creative Commons Attribution 3.0 Unported license

Light pollution is an ecological disturbance with multiple consequences. ALAN disrupts natural day-to-night rhythms such as singing and migration of birds, the activity period of small mammals, mating of frogs, nesting of bats and the orientation of sea turtle hatchlings. There is increasing evidence that humans are also sensitive to ALAN: it affects our circadian rhythm (the sleep–wake cycle repeated approximately every 24 hours), resulting in irregular hormone production, depression, insomnia and other maladies.

Insects couldn’t be immune to the effects of ALAN since much of their behaviour is dependent on light. We don’t know how insects see the world, but they recognize forms, detect movements and discern colours based on lighting patterns. Insects can monitor the position of the sun by the polarization of light, so they can navigate with precision. Light detection helps them to keep track of the photoperiod (day length), which is fundamental to preparing for the winter months. 

Many beetles, flies, lacewings, aphids, dragonflies, caddisflies, wasps and crickets are drawn to light, but moths’ compulsive and apparently suicidal attraction to lightbulbs or flames is the most familiar case of positive phototaxis (moving towards a light source) among insects. Moths are our better known nocturnal pollinators, so naturally their possible vulnerability to killer lights is a matter of concern.

© Fir0002, Wikipedia Creative Commons

It turns out that moths’ fatal attraction doesn’t seem to be that fatal because they are only drawn to light at relatively short distances. A few moths come to a blazing end, but most of them are beyond light’s dangerous pull. This is not to say that moths are safe from ALAN. When it’s not sufficiently dark, the production of sex pheromones and egg-laying are inhibited for some species, so that their reproduction is affected. Also, the window of time for courtship and mating can be severely reduced. Light pollution interferes with moths’ perception of colours and shapes, signals necessary for flower location. It also makes them more vulnerable to parasites and predators, either because they are easier to find, or their defence mechanisms (e.g., bat avoidance manoeuvres) are less effective in over-illuminated environments.

Light pollution disturbs many aspects of moths’ physiology and behaviour, although we can’t tell whether whole populations are being harmed: not all species respond equally, and there are many variables to be considered about the light source, such as wavelength, intensity, polarization and flicker. But from the little we know, excessive illumination can be added to the list of pressures on our moth fauna and consequently on pollination services. 

At a time of growing concern about global warming, light pollution may sound like a secondary problem. But the more scientists look into it, the more they learn that this is a serious environmental threat. And while sorting out the climatic mess will be tricky and complex, the light pollution problem is relatively easy. The first, obvious and straightforward measure is to turn off unnecessary lights. When illumination is needed, it could be dimmed, shielded or limited to specific areas such as pavements or roads.

Light designs and their impact on nearby biodiversity © AlexCairns, Wikipedia Creative Commons

Light dimming is good for the environment and for the economy too. When in 2018 the city of Tucson, USA, converted nearly 20,000 of their street lights to dimmable LED lights, the city saved £1.4m from its annual energy bill.

Preserving and protecting the night time environment is an important but neglected aspect of conservation. A darker world would benefit moths and other species, and it would be good for us as well. We could sleep better or go stargazing again. 

European artificial sky brightness on an increasing scale (black, blue, yellow, red) © Falchi et al. 2016. Science Advances 2(6) e1600377

Phoenix rising from the sand

By Athayde Tonhasca

As the waters subside in Germany and the country recovers from July’s catastrophic floods, naturalists may soon be able to evaluate the damage to one species caught in the deluge: the grey-backed mining bee (Andrena vaga). This bee is at home on river flood plains, grasslands, meadows, coastal areas, anywhere with alluvial soils – soil derived from sand and earth deposited by running water – and plenty of willows (Salix spp.) nearby.

A grey-backed mining bee © Ocrdu, Wikipedia Creative Commons

Female grey-backed mining bees dig their nests on spots of firm, sandy soil with sparse vegetation. The species is solitary, although females tend to nest close to each other in aggregations that can be thousands strong. Willows are their only source of pollen, but nectar is taken from a variety of flowers.

A grey-backed mining bee nesting aggregation © Mohra et al. 2004. Solitary Bees: conservation, rearing and management for pollination

Calamitous floods aside, to build a home on flood plains seems like a disaster waiting to happen. Water levels rise and fall, waterways change courses, river banks are washed away: riparian habitats are fragile and ephemeral. But none of this is the end of the world for grey-backed mining bees. Although floods may destroy large numbers of nests or even wipe out whole populations, these bees are well-adapted to disperse and colonise new places. In fact, fragmented populations dispersed over large areas are genetically similar, which suggests free and frequent interconnections between them.

Seven grey-backed mining bee nesting aggregations (red dots) in Germany © Mohra et al. 2004. Solitary Bees: conservation, rearing and management for pollination

Moreover, finding a new neighbourhood has a health benefit. Local populations of grey-backed mining bees grow steadily over the years, with more and more females sharing a nice nesting spot. These agglomerations do not go unnoticed by predators and parasites such as the nomad bee Nomada lathburiana. This parasite invades mining bee nests and lays an egg in the host’s brood cell; the invader’s larva emerges, kills the host’s egg or larva, then eats its provisions. A grey-backed mining bee aggregation targeted by parasites may contract by 50% in four years. But these population crashes are not all caused by natural enemies; some females just up sticks to build new nests on parasite-free sites.

The parasitic bee Nomada lathburiana © James K. Lindsey, Wikipedia Creative Commons

The grey-backed mining bee has been recorded intermittently in Britain since the 1930s, although its identification has not been confirmed until 2014. Currently this bee is confined to a few colonies is southern Britain: its populations may expand or be eliminated if nest aggregations are to be hard hit by rising waters. But even in this doomsday scenario, the grey-backed mining bee is not likely to be gone for long: wandering females in continental Europe should have no problem in crossing the English Channel and making themselves at home in Britain. This ‘here today, gone tomorrow’ lifestyle helps explain the difficulty in tracking the grey-backed mining bee and assessing its conservation status: it was labelled ‘endangered’ in 1987, ‘believed extinct’ in 1991, and ‘data deficient’ in 2020. As a species fine-tuned to transitory and unstable habitats, and highly adept at dispersing and colonising new territories, this unassuming bee takes natural disasters in stride; they are just facts of life.    

Spooked hikers and choughs chuffed to bits

By Athayde Tonhasca

During these unprecedented/strange/challenging times (pick your favourite cliche), many Britons have swapped their holidays abroad for the domestic great outdoors. This shift may help explain a spike in the number of bee swarm sightings along trails and in open spaces. In most cases, people are witnessing the comings and goings of the heather colletes (Colletes succinctus). This bee is usually found on heathlands, drier parts of moorland and coastal dunes – places with abundant heather (Calluna spp.) and heath (Erica spp.), its main sources of pollen.

A heather colletes © gailhampshire, Wikipedia Creative Commons

The heather colletes nests underground in bare or thinly-vegetated south-facing spots; sandy banks quickly warmed by the sun are particularly favoured. Each female digs a burrow, stocks it with pollen and lays an egg on the pollen mass. The larva feeds on the pollen and emerges as an adult the following year. 

Like many solitary bees, heather colletes nest close to each other, usually cheek by jowl. These aggregations can be massive: in one case, 60 to 80,000 tightly packed nests along a 100-m stretch of a river bank. Not surprisingly, these concentrations of swarming bees have prompted many a rambler to turn back or give a wide berth to the restless mob of honey bee lookalikes. Such precautions are unnecessary because these bees are harmless. They are not at all aggressive, and their stings are too weak to penetrate human skin. People who stop to admire them may catch a sight of clusters of bees rolling around. These are mating balls, comprising several males jostling furiously to mate with a female, who is hidden in the middle of the melee. As soon as a male succeeds – usually the larger one – the mating ball breaks apart. Females are monandrous, that is, they have one mate at a time, so they are not receptive to other males. 

Nest aggregations, which are common among several species of mining bees, are a bit puzzling because of the risks they represent. The abundance of provisions (pollen and nectar) stored by female bees, and so many juicy larvae and pupae in the same place are godsends to predators and parasites. 

So why do bees aggregate? It could be that adequate nesting sites are scarce: the ground has to be within certain physical specifications for secure tunnelling – the right type of soil, texture, drainage, slope and temperature – so several local bees may be attracted to the few good spots. Nesting needs help explain why many solitary bees display natal philopatry, which is the tendency to return to the site of their birth. It makes sense for a newly emerged bee to stick around: why take chances somewhere else when its place of birth ticks all the boxes? So the colony keeps growing, sometimes for decades. Aggregation may also result from having food nearby: broods have better chances of success if their mothers had easy access to pollen and nectar.

Whatever the reason, aggregations are quite handy for farmers who take advantage of the crop pollinating skills of some species such as the alkali bee (Nomia melanderi).

Alkali bee nests at the edge of an alfalfa field in America © Jim Cane, Agricultural Research Service, US Department of Agriculture

On the island of Colonsay, another species appreciates heather colletes nest aggregations: the red-billed chough (Pyrrhocorax pyrrhocorax). This bird feeds mostly on arthropods, and ants, beetles, moths and spiders are its usual prey. The choughs on Colonsay have learned to excavate heather colletes nests to get a nutritious, plentiful meal. 

A red-billed chough, a heather colletes predator © gailhampshire, Wikipedia Creative Commons

Hungry choughs are not likely to threaten heather colletes populations, considering the small number of birds on the island and their preference for farmland food such as crane flies and dung beetles; bee meals are probably opportunistic.

The heather colletes has experienced a small decline throughout Britain in the last 10 years or so for unknown reasons, but the population is still widespread and abundant in many places. They will probably carry on amazing and sometimes unintentionally startling nature ramblers for years to come.