When the night has come and the land is dark

By Athayde Tonhasca

Night is coming to an end in a Central American forest, and its nocturnal denizens – bats, owls, secretive rodents and cats – begin to retreat to their shelters. Before the crack of dawn, light levels are up to 100 million times dimmer than during the day, so it’s still too dark for the day shift inhabitants. 

Tropical forest understorey, which is never bright even in daytime © Bruno Henning, Wikimedia Commons.

But one creature is already busily going about in the dense tangle of vegetation: the halictid (aka sweat bee) Megalopta genalis is flying from flower to flower collecting pollen and nectar, then navigating safely back to its nest.  This is one of the 250 bee species, about 1% of the total bee fauna, known to be nocturnal (active at night) or crepuscular (active during twilight, dusk or dawn). This is a surprisingly large number, considering that bees are essentially adapted for bright sunlight.  

A Megalopta genalis from Panama © USGS Bee Inventory and Monitoring Lab, Wikimedia Commons.

Bees, like other insects and crustaceans, have compound eyes, which comprise thousands of independent light receptors known as ommatidia (sing. ommatidium). Images are formed by combining the input from the ommatidia, which are oriented in different directions – above, below, sideways and forwards. As a result of this configuration, image resolution is not very good. When a bumble bee hovers near you, it probably was attracted by the colour of your hat or your scent: it just wants to check whether you are a giant flower. Insects may not see clearly, but many of them have a large angle of view – a feature that makes flies and dragonflies so hard to catch. In some cases, they can also see polarised light, which we can’t.

Drawing of the compound eye of a drone fly from Robert Hooke’s Micrographia, 1664.

a. The single-chamber camera eye of humans: spatial resolution is achieved through the lens and a concave retina. b. An insect compound eye: spatial resolution is achieved through a series of small lenses and a convex retina. Striped areas indicate regions of photoreception. © Buschbeck & Friedrich. 2008. Evolution: Education and Outreach 1: 448-462.

In addition to their compound eyes, bees and most other insects have simple eyes (ocelli). These are single lens organs to detect movement and light, and they help bees navigate during flight. Daytime bees find their way by identifying landmarks around their nests and along foraging routes; directions and distances are also determined visually, with the help of polarised light.

Compound eyes and ocelli of the orchid bee Euglossa hansoni © Insects Unlocked, Wikimedia Commons.

But how does Megalopta genalis cope with very low light? We know that nocturnal bees can react to faint movements, see polarised light and orientate using landmarks just like diurnal bees, but how they do these things is not completely clear. Night-flying bees have larger compound eyes and ocelli when compared with diurnal bees, but there must be other factors at play such as neurological adaptations; eyes alone don’t explain their visual performance.

The ability to fly in low light evolved independently in bees from the families Andrenidae, Apidae, Colletidae and Halictidae, so there must be selective advantages for being nocturnal or crepuscular. They may be less vulnerable to parasites and predators, or there could be less competition for food. The night flyers may be responding to food availability: many plants bloom only at dawn or at night to save water, while others accumulate nectar through the night, offering rich rewards to early risers.

If you are wondering whether these night-time comings and goings have any consequences for plants, the answer is yes. Nocturnal bees pollinate a range of plants, many of economic importance. Several of these bees are good at buzz pollination, so they may be particularly important for plants with poricidal anthers such as Solanum spp. (e.g., aubergines, peppers and tomatoes). But we know little about nocturnal bees: collecting data about pollination ecology is hard enough during day time, and it becomes a real challenge when the lights are out. 

Night-flying bees are representatives of a vast number of nocturnal flower visitors such as moths, whose role as pollinators are becoming increasingly recognised. We need more night owl ecologists to help us understand better their role in our ecosystems.  

  

Nocturnal bees that visit flowers of cambuci (Campomanesia phaea), whose fruits are eaten raw or prepared into jellies, sherbets or juices. A: Ptiloglossa latecalcarata; B: Ptiloglossa sp.; C: Megalopta sodalis; D: Megommation insigne © Liporoni et al., 2020. Scientific Reports 10 15333.  

Hocus crocus, cast a spell with this magical bulb

If your mind is wandering towards spring already, and you are looking to help pollinators, chances are you are thinking what to plant in your greenspace, containers or garden.  You could do worse than to ponder on the value of the crocus.

A crocus with a bumblebee covered in pollen grains. ©Lorne Gill/NatureScot

Not only will it bring a welcome uplifting dash of early spring colour but it could be a lifeline for emerging queen bumblebees. And just as there is variety in the bumblebee world, so there is in the world of crocuses. We speak of it as if it were one variety, but there are many.

An array of colourful crocuses are available to lift the spirits come February and March. They are not far behind the snowdrop when it comes to announcing the impending arrival of a new spring. With their bright and breezy colours ranging from purple, through to a deep golden yellow they certainly do lift the spirits – a great example of the unsung health and wellbeing benefits of nature that we sometimes take for granted.

What do pollinators make of the humble but ever popular drifts of crocus?   Well, quite a lot it seems. Our spring-flowering crocus offer early nectar and pollen sources for bees coming out of hibernation. What’s more it is said that some queen bumblebees have been known to use the flowers as overnight sleeping berths.

That wonderful source of inspiration – the Bumblebee Conservation Trust website – is pushing the value of planting crocuses this October.  As they succinctly put it  “What can you plant for bumblebees in October? Our top picks are crocus bulbs, winter honeysuckle, pussy willow, and mahonia.”

The RHS website is an advocate too. Quick facts they publish include the reassuring news that although crocuses generally prefer sunny and well-drained sites, they are happy on a range of soils. 

Not surprisingly for a flower so vivid and popular there are several historical references to the crocus.

It is said that in 352BC a famous battle at ‘Crocus Field’ was written into ancient Greek history. Both the Romans and the Crusaders have been credited with introducing the bulbs to western Europe. There are references to use of the word crocus in Sanskrit, Greek, Hebrew and Latin so tracing the true roots of the name is shrouded in history. Homer, the author of the Illiad and Odyssey, is said to have lyrically compared a golden crocus to sunrise. A less cheerful association in Greek mythology is the tale of a young man called Crocus, a broken-hearted lover who was turned into a flower, two versions survive, neither ending well for the love-sick Crocus.

You might wish to bear in mind that there are both autumn and spring Crocus species. Colchium is an alternative name for the autumn crocus (and contains a drug called colchicine, which was used to treat gout).  But if you opt for the ever popular spring flowering crocus you will be helping out early emerging pollinators. And remember in that cooler time of the year you do get a chance to look more closely at the insects. 

Great fun for you, a vital lifeline for early emerging pollinators. Now that is a magic recipe.

Falkirk’s nature network

It’s been another busy year at Falkirk Council, and their work to help our hard-pressed pollinators has certainly been gathering momentum. I recently met Anna Perks, the Biodiversity Officer with the local authority, and she filled me on their fantastic progress.

“Habitat loss and fragmentation remain key issues facing our pollinators,” acknowledges Anna, “and Falkirk Council’s Sustainable Grass Management Pilot Project is one of our strands of work designed to tackle this issue.  Since 2021 we have created over 21 hectares of naturalised grass habitat, along with at least 2 hectares of wildflower meadow.”

This is impressive in its own right (bearing in mind that between 1932 and 1984 we lost over 90% of our natural grasslands in the UK), but when you consider that the Falkirk work was carried out in areas that were previously given over to short, amenity grass you can see that a shift in purpose is taking place.

The biodiversity team in Falkirk have also planted over 240,000 spring flowering bulbs and 47 fruit trees.  That’s a welcome addition to the pollinator resource, particularly as this offers a food source early in the season when we know that emerging queens are on the wing and scouring the landscape for a vital feed. 

It would be fair to say that the Falkirk approach is working well, but don’t just take my word for it.  Anna is delighted that surveys carried out on their sites are revealing improvement. “Surveys at six of their 35 pilot sites have identified 96 different plant species” she explains. “We have recorded over 90 invertebrate species in the meadow and naturalised grass areas.  That’s progress which compares very favourably to just a handful of plant species, and a maximum of 2 invertebrate species, in the short amenity grass at the same sites previously!”

The surveys have thrown a spotlight on some interesting insect species. Most of the invertebrates recorded depend on long grass and nectar-rich wildflowers to survive. Thus it was heartening to see the common green grasshopper which needs long grass to complete its life cycle, orange-tip butterflies feeding on cuckoo flower, and a variety of bumblebees as well as numerous hoverflies found feeding on the nectar-rich wildflowers. It’s amazing what can quickly thrive in areas where the grass had previously been mown short each year.

‘Second Nature’ is the 3rd Biodiversity Action Plan for the Falkirk Council area. It includes lots of actions and projects to help the area’s local wildlife. Working with many different organisations, community groups and individuals the local authority are making good progress on a range of challenges. Why not settle down in your favourite spot and enjoy this captivating booklet?   Inspiration is sure to follow.

Stop Press : Falkirk Council’s Executive Committee have now given approval for their pilot project to be mainstreamed, rolling out the changes to the way the council manages grasslands and greenspaces to other sites within the Falkirk Council area. It’s fantastic news and a real recognition by Falkirk Council of the positive benefits that the pilot project delivered for biodiversity, climate and health & well-being.

Further reading: 

Our January 2021 Falkirk update carried an interview with Anna.

In 2018 we carried a feature on the Falkirk Pollinator way.

A stinking trap or a cosy hideout

By Athayde Tonhasca

In a shady spot in a woodland somewhere in Britain, a lords-and-ladies (Arum maculatum) blooms. This plant is the only common British species of the mostly tropical family Araceae, so its flowering is nothing like what we would expect for a typical woodland dweller. Anytime from April to May, the lords-and-ladies produces a pointed shoot that unfurls into a poker-shaped structure called a spadix, which is enveloped by a hood-like membranous bract known as a spathe. The small flowers are clustered at the base of the spadix, hidden from sight. They are arranged as a ring of female flowers at the bottom and a ring of male flowers above.

L – A lords-and-ladies ©Sannse, Wikimedia Commons. R – From left to right: a fruiting stem, spadix and spathe, the spadix ringed with male and female flowers, and a tuber © M. Burnett, c. 1853, Wellcome Collection.

Spadices and spathes are typical of Araceae, the arum lilies or aroids. This morphological arrangement has enticed comparisons with certain parts of the mammalian anatomy, so Arum maculatum has been christened with colourful and suggestive names such as cows-and-bulls, stallions-and-mares, devils-and-angels, Adam-and-Eve, soldiers’-diddies, willy-lily, cuckoo pint and priest’s pintle (the meanings of old-English ‘pint’ and ‘pintle’ can be found by a quick etymological investigation). But the plant has inspired the pious as well, who preferred names such as friar’s-cowl, Jack-in-the-pulpit, or parson-and-clerk. Peter Law and Lynden Swift have written interesting pieces on lords-and-ladies’ historical aspects, including its many names, uses in popular medicine, and as a source of starch for stiffening medieval ruffs and beards.

Once the female flowers are mature and receptive, they start producing a scent whose dispersal is helped by the heat generated by the spadix. This biochemical process, known as thermogenesis, can heat the inflorescence up to 15 °C above the ambient temperature. Sharon Robinson, from the University of Wollongong (Australia), explains thermogenesis in the heat of the night.

Inflorescence of Philodendron melinonii photographed at about 19:00 h for the visible and infrared spectra © Seymour & Gibernau, 2008. Journal of Experimental Botany 59: 1353-1362.

Smell and warmth are irresistible lures to one particular customer: a female Psychoda phalaenoides. This is one of the 3,000 or so species of midge of the family Psychodidae. They are small flies (2-4 mm wingspan) covered in ‘hairs’ (actually hair-like scales). They are usually found in damp woods or near stagnant water, including drains and sewers, which are ideal places for egg laying and for the larvae to feed. Their appearance and habits explain their common names: owl midges, moth flies, drain flies or sewer flies. In warm countries, some of the 1,000 or so members of the sub-family Phlebotominae, the sand flies, feed on blood and can be vectors of diseases such as leishmaniasis. But sewer flies don’t bite, some of them don’t even feed in the adult phase. They are sometimes considered a nuisance because of their numbers.

Psychoda phalaenoides © Joseph Berger, Forestry Images.

One would expect that a creature dubbed ‘drain fly’ or ‘sewer fly’ would not be interested in run-of-the-mill, flowery scents. Indeed, botanist Cecil T. Prime, who wrote a whole book about the plant (Lords and ladies, 1960), described the aroma of its flowers as ‘foul and urinous’. That’s understandable; the scent contains chemicals such as 2-heptanone and p-cresol, which are also found in one of the fly’s favourite breeding sites – cow dung. So lords-and-ladies flowers are just irresistible to female P. phalaenoides (it’s not clear why only females are interested). The release of scents mimicking decaying organic matter to attract flies and beetles searching for oviposition sites or food is known as sapromyiophily. Besides Araceae, this type of deceitful attraction occurs in the birthwort (Aristolochiaceae), milkweed (Asclepiadaceae) and orchid (Orchidaceae) families. By the way, it’s only our human prejudice that leads us to believe that flower scents must be ‘nice’: a plant produces whatever smell it takes to bring in the right pollinator.

Venus and Cupid enjoying a garden’s aroma, with not an owl fly in sight. Allegory of smell by Jan Brueghel the Elder (1568–1625) and Peter Paul Rubens (1577–1640) © Museo del Prado.

A female midge alights on the spadix, crawl downwards through a ring of ‘hairs’ (modified sterile male flowers) and reaches a smooth-walled floral chamber at the base of the structure. She’d better like it there, because she will stay for a while: she’s trapped.

Details of a lord-and-ladies inflorescence © Fabelfroh, Wikimedia Commons.

Because of the tangle of hairs and slick walls, the midge cannot crawl back out of the floral chamber. But that’s not too bad: while confined, she can feed on nutritious secretions produced by the female flowers at the base of the spadix. From the plant’s point of view, incarceration is vital. The midge may have pollen attached to her body from previously visited lords-and-ladies; while she wanders around the chamber for 18 to 24 hours, there’s a good chance some of these pollen grains will be deposited on the receptive stigmas.

Hours go by, and things start to change. The male flowers, located higher on the spadix, begin releasing pollen, which rains on the entrapped midge. By next day, the female flowers no longer discharge scent or secrete food, the spadix stops producing heat, and the hairs wilt. Now the pollen-laden midge is allowed to leave. Alas, freedom is ephemeral: the escaped fly is soon attracted to another inflorescence, and the process is repeated. Cross-pollination ensues.

This type of plant-insect relationship involving coercive detention is known as entrapment pollination, which is one of the oldest pollination systems. Nymphaeales (the order consisting of water lilies and other plants) and beetles have been playing this game for approximately 90 million years, and it has worked nicely for both gaolers and gaoled.

Psychoda phalaenoides is the only known pollinator of lords-and-ladies in Britain, but other drain flies, fungus gnats (Sciaridae), non-biting midges (Chironomidae) and small dung flies (Sphaeroceridae) pollinate this plant and other Arum spp. elsewhere. And there’s so much more to be discovered: Gfrerer et al. (Frontiers in Plant Science 12: 719092, 2021) recorded 289 lords-and-ladies floral volatiles from different plant populations in continental Europe, the highest figure ever found in a single plant species. This high diversity of scents probably reflects the requirements of an equally diverse fauna, one that is not normally associated with pollination: the non-syrphid Diptera, that is, flies other than hover flies – “the forgotten flies” (Orford et al., 2015. Proceedings of the Royal Society B 282: 20142934). 

As we learn more about these and other seemingly drab insects and their intricate relations with plants, we may start showing them greater appreciation. Even to the humble drain flies. 

The Solomon’s lily (Arum palaestinum) has been used for millennia as food and medicine by Middle East Arabs, Palestinians and Jews © Seán A. O’Hara. Its floral scent smells like fermenting fruit or wine and attracts fruit flies (Drosophila spp.) © Aka, Wikimedia Commons.

Is the sward mightier than the pen?

Edinburgh is a city of traditions. Take the Edinburgh International Festival, and the Fringe and Tattoo which followed, all living examples of the capital city’s great love of a good time. Edinburgh Living Landscape is similarly successful in pushing a sound idea that heralds good times.

Visit the website of Edinburgh Living Landscape and you get a sense of better things in store for nature in our capital.  It tells the eager reader that “Edinburgh Living Landscape is a network for nature in our city. We think it is crucial for the future health, happiness and wellbeing of Edinburgh’s people and wildlife.

“Our  programme will demonstrate that investment in the natural environment makes economic sense, as well as increasing biodiversity and creating healthier urban ecosystems. 

“To do this we need to integrate nature into neighbourhoods across the city. Edinburgh Living Landscape will work to benefit local people and wildlife with an aim to make the city one of the most sustainable in Europe by 2050.”

That’s as good as it gets when it comes to statements of intent for nature. What’s more with an impressive list of partners you just sense that this is a project that will deliver, time after time. With bodies including Scottish Wildlife Trust, The City of Edinburgh Council, The Conservation Volunteers, Royal Botanic Garden Edinburgh,  Greenspace Trust, The University of Edinburgh, Butterfly Conservation Scotland, and RSPB you know that local people and native wildlife are in good hands.

The drivers behind changing the way we mange public spaces have never been more compelling. From the early 1930s there began a systematic loss of beneficial grasslands for nature, by the time a mere 50 years had come and gone that loss of habitat, and the food sources that went with it, was depressingly mainstream. Urbanisation, development pressures, intensive farming .. and so the list of challenges went on. 

And the damage didn’t stop there.  What was actually left even in urban areas was subject often to harsh management, including routine spraying and chemical treatments. This simply compounded the crisis. Something had to give, and thankfully it was the depressing descent into devastating loss that gave.

Today we are better informed. We know that creating and managing habitats specifically for nature is the way forward. This is particularly so if we want to achieve nature restoration and tackle climate change. It’s therefore great that our capital city is taking significant steps to ensure that on their patch habitat loss is reversed.

The method is a swing away from the old way of doing things towards a mixture of relaxed mowing regimes, sensitive planting and more sympathetic management of greenspaces for nature. Edinburgh has embraced a mixed approach. Take meadow creation and management as one example. There are a variety of meadows to find and enjoy in and around Edinburgh. By far the bulk at wildflower meadows. However, there was a stunning designed or pictorial meadow at Royal Botanic Gardens Edinburgh and this was a powerful way to get people thinking and talking about meadows. This approach can be, as the excellent Plantlife website explains, a means to an end, as it ‘… crucially, starts warming attitudes – opening minds to other possibilities beyond the mown ‘neat-and-tidy’ approach. You can see the bees and butterflies.”

Informative signage is increasingly important too. Perception has a vital role to play particularly when changing the management regime of public facing amenity grasslands leads to transformation which isn’t often an overnight fix. Where people are used to neat, clipped, mown parkland it often requires a little explaining to extol the virtue of letting the grass grow longer, planting for pollinators and letting nature take its course. 

Whist at their peak meadows speak for themselves, it is the case that when freshly mown, or lying dormant, you have to sometimes work to ‘sell’ what is going on.  Then it helps to explain that the space – viewed by some as superficially scruffy – is actually being managed for nature and that what lies before the curious onlooker is perfectly normal … and beneficial. It will offer a home for nature and not just a forage for food source, it’s a habitat that offers shelter, nesting sites and overwintering opportunities. Generally people get that and are receptive to positive messaging.

So when next you visit Edinburgh and soak up the cultural delights, bear in mind that across the city there are good things happening for nature. Nature restoration is rarely a quick fix, but in a city famed for being more cerebral than most it is arguably culture at its highest.