The CrowdScience team like a challenge. And listeners Jenny and Kai in the UK have come to us with a big one. They want to know how many flies have ever existed.

Flies first appeared around 270 million years ago, so presenter Caroline Steel prepares herself to calculate a very, very large number indeed. She enlists the help of Dr Erica McAlister, Curator of Flies at the Natural History Museum in London. As Erica introduces her to specimens from the Museum’s collection of over 30 million insects, they start with the basics. Like... how do you define a fly in the first place?

Caroline also explores the incredible diversity of flies… from fast-moving predators like robber flies which catch other insects on the wing to midges which are a vital part of chocolate-production; and from blood-sucking mosquitoes which transmit fatal diseases to the housefly buzzing lazily around a room.

And that leads to another fly-related question. Listener Brendan in Colombia wonders why they always fly in circles around a particular area of his apartment. For an explanation we turn to Prof. Jochen Zeil from the Australian National University who reveals that this apparently aimless behaviour is, in fact, a battle for sex.

And Collin in Barbados has e-mailed to ask how flies and mosquitoes benefit us. He’s had first-hand experience of their negative effects through contracting the disease chikungunya from a mosquito bite so he’s wondering if these insects are anything other than a nuisance. However, passionate fly advocate Erica McAlister is ready with plenty of reasons that we should be extremely grateful for them!

Contributors:

Presenter: Caroline Steel

(Image: Close-up of insect on leaf, Kageshwori Manohara, Bagmati Province, Nepal. Credit: Aashish Shrestha via Getty Images)

It’s hard to imagine something as mind-bogglingly small as an atom.

But CrowdScience listener Alan has been attempting to do just that. All things in nature appear to be different and unique; like trees and snowflakes, could it be that no two atoms are ever the same?

Alan isn’t the first person to wonder this. Philosopher and scientist Gottfried Leibnitz had a similar idea in the 17th century; in this episode, philosopher of physics Eleanor Knox helps us unpick the very idea of uniqueness.

And with the help of physicist Andrew Pontzen, presenter Anand Jagatia zooms into the nucleus of an atom in search of answers. Listener Alan has a hunch that the constant movement of electrons means no atom is exactly the same at any given moment in time. Is that hunch right? We discover that the world of tiny subatomic particles is even stranger than it might seem once you get into quantum realms.

Can we pinpoint where uniqueness begins? And if the universe is infinite, is uniqueness even possible?

In the podcast edition of this show, we peer into that expansive universe, as we discover that the quantum world of hydrogen - the tiniest and most abundant of all atoms - allows us to observe galaxies far, far away.

Presented by Anand Jagatia

(Photo: Twelve snow crystals photographed under a microscope, circa 1935. Credit: Herbert/Archive Photos/Getty Images)

Listener Julie lives close to the coast in New Zealand and wants to know why the water that washes up on the beach isn't fresh. How exactly does all that salt get into the world's oceans?

In India, a country where salt became symbolic of much more than well-seasoned food, host Chhavi Sachdev visits coastal salt farms and a research institute dedicated to studying all things saline, to better understand our relationship with salty seas.

The team also ventures to a very briny lake on the other side of the globe in Salt Lake City, Utah, to learn how salt makes its way into water bodies.

Speaking to an expert in deep sea exploration, we learn how hydrothermal vents may play a role in regulating ocean saltiness, and how much the field still has to explore.

Meanwhile, listener Will wants to know how much melting ice sheets are affecting ocean salinity. But ice melt isn’t the only thing affecting salt levels when it comes to the impacts of climate change.

And... how many teaspoons of salt are in a kilogram of sea water anyway? We do the rigorous science to answer all these salient saline questions.

Featuring:

Presenter: Chhavi Sachdev

(Photo: Shiv Salt Works, Bhavnagar, Gujarat in India. Credit: Chhavi Sachdev, BBC)

CrowdScience listener Eleanor was lying in bed one rainy evening, listening to the radio. She lives in New Zealand, but happened to hear a weather forecast that told her it was raining in the UK too.

She started wondering: could it be the same rain falling there and outside her window in New Zealand? Can a raindrop really travel all the way around the world?

There are a number of routes the droplet could take, including traveling as moisture in the air. Presenter Caroline Steel meets meteorologist Kei Yoshimura, who puts his powerful weather simulation to work plotting the raindrop’s journey through the sky.

What if the raindrop falls along the way and gets trapped? Where might it end up? Hydrologist Marc Bierkens talks Caroline through the detours it could take, ranging from short stop-offs in plant stems to extremely long delays in deep groundwater.

Finally, could the drop of water make it to New Zealand by circulating through the world’s ocean currents? Oceanographer Kathy Gunn maps the droplet’s path through the ocean – and explains how climate change might affect its journey.

Featuring:

Presenter: Caroline Steel

(Photo: Textures of rain on the surface of the ocean. Credit: Philip Thurston/Getty Images)

It’s often said that fine wine gets better with time, and this week’s oenophile listener Jeremy has a cellar full of dust-covered bottles. He is curious whether chemistry can account for the range of flavours that develop as wine matures, but also wonders why some of it tastes like vinegar if you leave it too long?

(Photo: Aged bottles on wine racks in a cellar. Credit: Morsa Images/Getty Images)

The Blue Ridge Parkway is 469 miles of beautiful vistas, a mountainous road that winds from Virginia to North Carolina in the USA. The route is peppered with elevation signs, telling you how many metres above sea level you are. Which has CrowdScience listener Beth wondering: as we are told that sea level is rising, will all the elevation signs need repainting?

It’s a task she’s passed over to the CrowdScience team, who like a difficult challenge. The height of an enormous pile of rock like Ben Nevis, or Mount Everest feels unchangeable. But we measure them relative to the nearest patch of sea, which is where our story becomes complicated. Unlike water in a bath, sea level is not equal around the world. The east coast of America has a different sea level to its west coast. And as host Marnie Chesterton discovers in Finland, in some parts of the world the land is being pushed up, so sea level is actually falling.

In fact, when nothing on earth - not the sea, the shore or the mountains - seems to be stable or constant, the question of what you measure from and to becomes incredibly tricky. But that hasn’t stopped oceanography and geography scientists risking life and fingers to use an ever-evolving array of technologies to find answers. In this show we find out why they care so much, and why we should too.

Featuring:

Presented and produced by Marnie Chesterton

(Photo: Sea Level Elevation Sign in Death Valley, California. Credit: Mitch Diamond/Getty Images)

Prayer and meditation are key features of religious and spiritual practices around the world, suggesting they’re intimately linked to the human condition. But what is going on in the brain during prayer? And is praying beneficial for our mental health?

CrowdScience listener Hilary is keen to find answers to such questions. She’s a counsellor with a strong Christian faith, and is curious to know whether science can illuminate religious and spiritual practices.

Presenter Caroline Steel talks to neuroscientists researching how our brains respond to prayer and meditation; and practices mindfulness herself to explore its similarities to prayer. She discovers that having a relationship with God may depend on more than religious practice. And is there a ‘spiritual part’ to our brains? Or is prayer just one activity among many - like going for a walk or playing music - that can have similar effects on our state of mind?

Featuring:

Presenter: Caroline Steel

(Photo: A crowd of people praying. Credit: Digital Vision/Getty Images)

Mosquitoes are responsible for more human deaths than any other animal. These tiny creatures transmit many diseases, but the most devastating is malaria. It kills over half a million people every year, most of them children.

So why are people still dying of malaria in such large numbers, when so much time and money has been invested in trying to eradicate it? What do we know about mosquitoes and malaria, and what do we still need to learn? CrowdScience visits Malawi, one of the African countries leading the way against malaria, with the rollout of the world’s first malaria vaccine programme.

Presenter Caroline Steel is joined by a live audience and a panel of experts: Wongani Nygulu, Eggrey Aisha Kambewa and Steve Gowelo. Together they explore questions from our listeners in Malawi and around the world, like why female mosquitoes feed on blood while males drink nectar; why some people are more likely to be bitten by mosquitoes than others; and how we might modify the insects’ DNA to stop them spreading diseases.

About half a million children across Malawi have been vaccinated since 2019. We visit a clinic in nearby Chikwawa to meet the staff involved in the vaccination programme there, and the mothers embracing the opportunity to protect their babies against this deadly disease.

Recorded at Malawi Liverpool Wellcome Trust (MLW), Blantyre, Malawi.

Contributors:

Presenter: Caroline Steel

(Photo: A mosquito, that is silhouetted against the moon, bites a human arm. Credit: LWA/Getty Images)

When CrowdScience listener Israel from Papua New Guinea received a bad grade on a maths test in third grade, he looked around the class and realised that almost all the other students had received a better result. Since then, he has always wondered: why are some people better at maths than others?

(Photo: Boy scratching head in front of blackboard. Credit: Jose Luis Pelaez Inc/Getty Images)

Coastlines around the world are changing, causing serious problems for the many communities living near the sea, as well as vital and fragile coastal ecosystems.

In the second of a two-part special on coastal erosion, CrowdScience explores the best ways to tackle this problem. Presenter Caroline Steel visits the Caribbean island of Puerto Rico to see the various methods they use to protect their coasts.

First up: ‘riprap’ – rocks strategically placed to keep the encroaching sea at bay. The problem is, while it protects the area immediately behind the rocks, riprap can exacerbate erosion nearby.

But there are other, more nature-friendly solutions, including sand dune restoration. Caroline picks up her shovel and helps to re-plant dunes, destroyed in the past by erosion as well as sand extraction for the construction trade. The roots of these plants stabilise the dunes, while building boardwalks prevents further damage from humans.

Nature also offers the perfect offshore protection against coastal erosion: coral reefs. These are the first line of defence in absorbing the power of the ocean’s waves. Down on the beach, we see for ourselves just how effective they are. The reefs face threats, but restoration plans are afoot. We visit a nursery that grows corals to plant out on the reefs – and find out about corals’ surprising cannibalistic tendencies in the process.

Featuring:

Presenter: Caroline Steel

(Photo: Coast restoration measures at Ultimo Trolley Beach, Puerto Rico. Credit: BBC)