Canary Media’s Down to the Wire column tackles the more complicated challenges of decarbonizing our energy systems.

This is part two of a three-part Down to the Wire series this week on how the federal government should design rules for the hydrogen tax credit under the Inflation Reduction Act. Read part one.

Truly ​“green” hydrogen needs to be made with truly carbon-free power. But will strong hydrogen tax-credit rules that require the use of truly carbon-free power make it harder to create a green hydrogen industry that can compete economically against fossil fuels?

Yesterday we walked through the case for the federal government to set rigorous rules for the 45V hydrogen production tax credits, which will be worth tens of billions of dollars; clean-energy advocates want to require producers to meet a high bar for the clean energy that fuels their process. Today we consider the opposing case, which argues that looser rules are needed to get the clean hydrogen sector off the ground.

Many of the parties calling for strict rules have cited an analysis by Princeton’s Zero Lab that finds that hydrogen made from grid electricity will lead to net increases in carbon emissions unless production is paired with clean energy on an hourly basis. It also indicates that hydrogen production that uses genuinely carbon-free power can be cost-competitive with hydrogen made with fossil gas, thanks to the generous size of the tax credits — even when the clean hydrogen producers are required to follow strict applications of the principles of additionality, deliverability and hourly matching (see part one for definitions of these terms).

But Zero Lab’s analysis is not the only one out there. Many of the companies submitting comments to the IRS say that requiring additional, deliverable and hourly matched clean energy to power electrolysis could push costs above those for hydrogen made with fossil gas, limit production to only those parts of the U.S. with the highest amounts of clean energy, and undermine the country’s push to become a leader in low-cost hydrogen production.

As Jesse Jenkins of Princeton’s Zero Lab told Canary Media, ​“There isn’t really much of a question about the veracity of the emissions analysis we’ve performed. The main response from those seeking to develop electrolyzer projects and make the most money is that this is too onerous and would raise project costs too high to be profitable.”

Even a recent report by energy consultancy Wood Mackenzie that’s being cited by NextEra and other opponents of strict rules finds that ​“green” hydrogen production could lead to increased carbon emissions. WoodMac determined that ​“absolute emissions increase marginally” under the scenario it modeled for low levels of hydrogen production in Arizona and South Texas — even though those two states have relatively high percentages of renewable energy in their grid mixes.

“It is expected that the outcomes would vary significantly on a regional basis and may also vary as hydrogen production scales well past the addition of a 250 MW electrolyzer in a region,” the report’s authors write in a March op-ed.

The arguments against strict clean-energy accounting: Cost and competitiveness

WoodMac’s analysis is more clear regarding its findings on the cost of hydrogen made via annual matching versus hourly matching of clean energy. It found that making hydrogen under hourly-matching requirements would be 60 to 175 percent more expensive than making it under annual matching — a cost increase that ​“could result in unfavorable economics for green hydrogen adoption.”

That cost increase is central to arguments made by Plug Power against strict rules for the hydrogen tax credits. The company, a maker of hydrogen fuel cells, is planning to invest more than $1 billion in hydrogen electrolysis facilities in California, Georgia, Texas and its home state of New York.

“Until all those renewables are available on the grid, you’re still going to have to [power production with] natural gas and other resources,” said Roberto Friedlander, the company’s director of investor relations. Plug Power plans to buy renewable energy credits for all its sites to meet ​“green” hydrogen production requirements, directly use solar power to make cleaner hydrogen in Texas and hydropower in New York, and eventually build clean power to supply its electrolyzers, he said.

But if eligibility for those tax credits is restricted to hydrogen produced with newly built clean energy delivered from where it’s produced to where it’s consumed on an hourly basis, Plug Power’s electrolyzers won’t be eligible for the credits and thus won’t be able to compete on cost with hydrogen made from fossil fuels, he said. That’s particularly true if today’s ​“gray hydrogen” producers are allowed to qualify by adding carbon-capture-and-storage systems to their steam-methane-reforming sites to produce so-called ​“blue hydrogen” — something that’s not cost-effective today, but would be eligible for tax credits if the Treasury Department’s final eligibility rules deem it sufficiently low-carbon to earn the incentive.

“You have to have government intervention to help these nascent clean-energy industries,” Friedlander said. ​“How else can you inspire people to take on the risk of these investments?” 

These cost concerns are echoed broadly in comments to the IRS and Treasury Department from a range of companies and trade groups arguing against hourly matching. 

BP America, a division of U.K.-based oil giant BP, stated in comments to the IRS, ​“Stringent requirements such as hourly zero-emission matching have the potential to devastate the economics of clean hydrogen production. Moreover, such restrictive requirements are likely not practical or feasible in these early stages. If a green hydrogen production facility can only produce during hours when wind and solar are available, the low utilization rate will dramatically increase the price of the hydrogen produced.”

NextEra’s comments to the IRS use the same phrasing as BP America’s in claiming that hourly time-matching would ​“devastate the economics of clean hydrogen production,” adding that it ​“would not align with legislative intent to accelerate progress towards a clean hydrogen economy.”

NextEra — the parent company of utility Florida Power & Light and clean-energy developer NextEra Energy Resources — has made hydrogen central to reaching its goal of zero carbon emissions by 2045. The company’s large-scale hydrogen electrolysis plans include a project in Florida at its Gulf Clean Energy Center fossil-gas power plant that would be powered by Florida Power & Light solar projects and a project in Arizona in partnership with industrial-gas producer Linde, NextEra Chief Communications Officer David Reuter said in an email.

“An hourly match requirement would drive up the price of clean hydrogen and reduce investment by equipment manufacturers,” he wrote. 

NextEra also stated in its IRS comments that an internal analysis it conducted indicated that hourly clean-energy matching ​“would increase the cost of green hydrogen production by around 70%–170% versus annual matching, eliminating the ability of the [production tax credit] to make green hydrogen cost competitive with other forms of hydrogen.”

That cost estimate was echoed in comments from the Edison Electric Institute, a U.S. utility trade group, which used language nearly identical to NextEra’s. Like the cost estimate from Wood Mackenzie, it is significantly higher than the estimates from Zero Lab, which found cost premiums for hydrogen produced via hourly matched clean energy on the Western U.S. electricity grid would be only 20 to 50 cents higher than a base price of $2.50 to $3.50 per kilogram.

Location matters: Deliverability and geography

NextEra and Edison Electric Institute lay out some key reasons why they say hourly matching will drive up costs. One has to do with location, or more precisely, the fact that some parts of the country have less clean energy than others.

Edison Electric Institute noted that requiring hourly matching would disadvantage producers in some geographical areas. ​“Although hourly matching may be achievable more quickly in certain regions of the United States with the appropriate renewable generation mix, it will take longer in many other parts of the United States,” it wrote.

And NextEra wrote that hourly clean-energy matching would require green hydrogen projects to ​“buy time-correlated renewables during periods of under-generation, which corresponds to higher market price periods.”

But proponents of strict hourly matching rules point out that the availability of clean energy ought to be a primary factor in deciding where to produce green hydrogen. That’s not just because clean energy is a vital input to producing carbon-free hydrogen, they say. It’s also because electricity prices — a major factor in hydrogen costs — are usually lower at times when clean energy is plentiful and higher at times when electricity demand spikes and a higher proportion of fossil fuels are used to make up the balance.

“The levelized cost of hydrogen is very much driven by the cost of energy,” said Beth Deane, chief legal officer at Electric Hydrogen, which is advocating for stringent tax-credit rules. ​“And the fortunate thing is that the cost of energy is also lowest when the carbon[-intensity of grid electricity] is lowest — when you have a grid that’s pouring off energy because it’s not needed.” Those price differentials are likely to become more pronounced as the country adds increasingly more low-cost solar and wind power to meet its climate goals.

In its comments to the IRS, Electric Hydrogen cited data from the California grid, which is awash in low-cost solar power at midday but sees energy prices spike when gas generators are cranked up to serve peak demand on hot summer evenings. This graphic from Electric Hydrogen cites data from CAISO, California’s grid operator, showing that the cost and carbon-intensity of electricity are generally correlated in that state. But this dynamic is not currently replicated across all parts of the country.

Deane pointed out that some of the arguments against strict hourly matching are being put forward by companies that have already made plans to invest in hydrogen production in areas that lack ample renewable resources today. Plug Power’s first hydrogen facility is being built in Georgia, a state with a current power mix of 47 percent natural gas, 16 percent coal, 24 percent nuclear and 8 percent renewables. Florida, the home of NextEra-owned utility Florida Power & Light, gets 75 percent of its power from natural gas, 5 percent from coal, 13 percent from nuclear power and less than 1 percent from renewable energy.

Under current accounting methodologies based on annual renewable energy credits, those plants would be able to claim to be powered by clean energy produced anywhere in the country — including clean energy that has no connection to the grid that actually powers them.

That’s why calls for hourly matching of renewables are being married with calls for deliverability, or requiring that the clean energy being claimed is physically capable of reaching the electrolyzers using it.

Such deliverability rules would, by their nature, privilege hydrogen being produced in more renewable-rich regions. The American Clean Power Association, an industry trade group that counts NextEra Energy Resources as one of its members, said in its comments to the IRS that if electrolyzers can only produce during hours when clean energy resources are available, ​“the low utilization rate can dramatically increase the price of the hydrogen produced.”

Image: Elvis Tam / 500px via Getty Images

Research into sun and heat-deflecting technologies to tackle climate change are proceeding at a rapid pace around the globe, prompting the United Nations Environment Programme (UNEP) to investigate their potentials and dangers while stating that these controversial interventions are humanity's "only option" to quickly cool the planet within years.  

“Solar geoengineering is getting mainstream in a way that’s almost inevitable that we’re going to do it”

“SRM technologies, should they be considered at some point in the future, do not solve the climate crisis because they do not reduce greenhouse gas emissions nor reverse the impacts of climate change. The world must be crystal clear on this point,” she said in a UN media release.

The biggest argument against solar geoengineering is that pursuing it draws attention and funding away from the effort to reduce greenhouse gas emissions. 

“Solar geoengineering is about modifying the climate for everyone”

Stephens is also skeptical that it’s even possible to coordinate an international effort to first study then keep geoengineering in check, she said, when that hasn’t been possible for other climate change efforts. 

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When Nicola Kagoro returned to Zimbabwe after a five-year stint as executive chef at one of Cape Town’s premier vegan restaurants, her vision had been to take what she had learned about affordable plant-based food and bring it home to Harare.

“Our dinners were six-course vegan meals with an international vegan chef: me,” she says. However, she soon had a bruising realisation: back in 2016, when she was first setting up, local people simply had no interest in buying what she was selling.

“There was no vegan culture in Zimbabwe,” says Kagoro, founder of the cookery business African Vegan on a Budget, who goes by the professional name Chef Cola. “[People] didn’t understand how you could have a six-course meal without meat. We were literally charging just US$1 for people to come to the dinners.”

After a while, however, attracting people to Kagoro’s table became less of a struggle. Her reputation from Cape Town reached the Zimbabwean capital and veganism, or at least plant-based food, became almost trendy. “[The dinners] went from $1 to me charging close to US$60 [£50] to have a seat at the table,” she says.

Now Kagoro, 34, has fronted a cooking slot on Zimbabwean television, is launching a takeaway service in March, and has thousands of followers on social media to whom she extolls the virtues – ethical, health and economic – of ditching animal products. “I think there are more African vegans coming out of the closet now,” she says. “They just didn’t speak about it before.”

For the past 40 years or so, Africa’s middle class has been growing, albeit with huge geographic variations – and linked to that growth are changing lifestyles and consumption patterns. Fast-food giants arrived on the continent and tapped into a clientele with more disposable income than ever before.

One of the results, say vegan entrepreneurs, chefs and activists, is that in many places meat and dairy have gone from rare luxuries to everyday staples. And that, they say, is not good for anyone: not for the planet, for animals, for people’s health – or their wallets. Together, they are trying to fight back, and although the number of people identifying as vegan is still tiny, the 1.2 billion-strong continent could yet prove vital for the direction of the global vegan movement.

“Nigeria will be the third most populous country in the world in 25 years,” says Hakeem Jimo, 51, co-founder of Nigeria’s first vegan restaurant, Veggie Victory. “So all the veganism in the UK and the Netherlands … sorry, it’s great, but the numbers are going to be decided somewhere else.”

What gives people such as Jimo and Kagoro hope is that while the term “veganism” is still viewed by most Africans as a diaspora-driven western import, plant-based diets are deeply embedded in the continent’s traditional way of life.

Marie Kacouchia, the Franco-Ivorian author of the cookbook Vegan Africa, published in English last month, says that during her research she did not encounter anyone calling themselves a vegan in Ivory Coast “who was really from [there] and not an expat”. But she did meet a lot of people who stick steadfastly to a plant-based diet simply because that is what they have always known. “They will not label themselves vegan, because … it’s not something that is in their representation,” she says.

That does not mean they are any less vegan. Kacouchia recalls a woman in her family’s village who told her she could not even conceive of regularly eating meat or other animal products. “She did not grow up eating meat and her diet would be completely transformed if she had to include it,” she says.

Kacouchia’s book is replete with coconut milk and cacao, plantain and cassava, watermelon and mango, at least in part a capturing of her childhood memories: of her mother’s fragrant stews, of fried plantain on the beach after church. It is also, she says, an attempt to bust some myths about the traditional African diet, namely that it is inherently meat-heavy and unhealthy.

“It was about inspiring Africans and people of African heritage to look at their diet differently and to also understand their origins, away from this European-centric vision that we have that is narrated by colonialism,” she says. “We want to make African people proud again, and we want them to regain faith in themselves, and to reinvent a veganism that is not European-centric.”

One country with its own distinctive form of veganism is Ethiopia, where the Orthodox Christian community (with about 32 million members, according to a 2007 census) fasts for at least 180 days a year. When breaking their fast, or tsom in Amharic, the nation’s Orthodox Christians must not consume any animal produce and therefore eat a diet that is vegan by another name.

For Helen Mebrate, a UK-based Ethiopian vegan who shares mouthwatering recipes on Instagram as @Ethiopianfoodie, this rich food tradition provides all anyone could need, from shiro wot (roasted and ground chickpea stew) to alech (seasoned carrots, potatoes and beetroot).

But she fears it is increasingly at risk. “It’s a bit sad to see so many burger places, so many meat places [in cities such as Addis Ababa]. And nowadays when you Google Ethiopian food … one of the first images that you see is meat dishes and I’m like, ‘since when did this become a thing?’ It’s changing so much. But when I was growing up, it was very much like a rainbow plate, with loads of pulses and greens.”

It is to try to fight back against this rapidly changing landscape that people such as Nabaasa Innocent, founder of the Uganda Vegan Society, are mobilising. In January the Kampala-based activist coordinated the first ever Africa Vegan Restaurant Week, an effort to showcase dozens of venues across the continent that are either vegan or offer vegan dishes.

“Some of these local restaurants don’t even have an online presence. So we thought as Africa it’s high time we united … [to] promote the options, because they are readily available,” she says. A concern for animal welfare drives Innocent’s veganism but more persuasive arguments for most Ugandans, she admits, are health and cost.

“Plant-based foods are more affordable and more available,” she says. “For example, to buy a kilo of goat meat I need about 20,000 Ugandan shillings [£4.50]. But then to buy a kilo of beans I need 5,000 Ugandan shillings or even less. Now that’s the best quality of beans but even at 3,000 Ugandan shillings, which is basically less than $1, I can still find a kilo of nice beans.”

A big part of the challenge, she and others say, is showing Africans that vegan food is not alien and not just about limp bits of bland tofu. “I mean, there’s only so much tofu one can eat, right?” jokes Olaoluwa Fashola, a British-Nigerian who moved to Lagos to open Casa Vegan, a business selling plant-based meat alternatives out of ingredients including jackfruit, cassava and locust beans: “That gives it that African-ness that we wanted.”

Born out of frustration with the lack of vegan options available to him when visiting family in Nigeria, Fashola’s vision was given extra impetus when his father died of cardiovascular disease in 2021. “It gave me the drive to push things forward,” he says, noting the health problems that a growing number of Africans face due in part to changing lifestyles and consumption habits, a connection that “a lot of people don’t appreciate”.

To begin with, Fashola says, his father had a typical reaction to his business idea: “If you speak to every African parent, they probably laugh at you when you say you’re vegan, and they offer you chicken or they offer you fish,” he says, laughing. “Initially, it was the same thing [with my dad]. It took a lot of education and I had to send him a lot of articles. And I think the more time he had to understand it, the more he came on board.”

Before he died, his father had come full circle, even nurturing a vision of a fully plant-based restaurant in a hotel he wanted to build. The change in his attitude, Fashola believes, could be mirrored across the continent. “He was coming along gradually. I think that’s the process within Nigeria, within Africa. I think it’s a slow burner. But with the right strategic influencers that can help us create the right noise … I feel like there’s a percentage of the market that would appreciate what we’re trying to do.”

There are some goals, however, that remain elusive, at least for now. Jimo, who spent years coming up with the right formula for his meat alternative – just chunky and chewy enough to suit the Nigerian palate – has now set his sights on something more complicated. “We’re still trying to fake a goat head,” he says, laughing. “That’s one of the delicacies here. The first plant-based goat head!”

Cauliflower yassa with olives

Prep 15 min
Rest 1 hr
Cook 35 min
Serves 4

You may have already heard of yassa, a traditional Senegalese dish made with chicken or fish. Yassa is a staple of west African cuisines. This is my vegan version using cauliflower. Its dense texture makes it a lovely substitute for chicken. Serve with white rice.

Juice of 1 lemon
2 tbsp mustard
2 garlic cloves, minced
1 tsp freshly grated ginger
Salt
Black pepper
1 large cauliflower, chopped
6 medium onions, thinly sliced
½ cup (65g) green olives, pitted
3 tbsp olive oil
1 bunch parsley, chopped
1 tbsp coconut sugar
2 bay leaves

1 Mix the lemon juice, mustard, garlic, ginger, salt and pepper in a large bowl. Add the cauliflower, onions and olives, and toss to coat. Marinate for at least an hour (or overnight in the refrigerator).
2 Remove the cauliflower from the bowl and set aside.
3 Heat 2 tbsp of the oil in a non-stick saucepan over a medium heat. Add the onions and marinade mixture and cook until translucent, about 5 minutes. Add the parsley, sugar and bay leaves and mix well. Add 3 tbsp water, cover and simmer until the onions have softened, for 10 to 15 minutes.
4 Heat the remaining oil in a frying pan over a medium-high heat. Add the cauliflower and cook until tender and golden brown, 15 minutes.
5 Stir the cauliflower into the onion mixture. Adjust the seasoning to taste and enjoy while hot.

• Recipe from Vegan Africa: Plant-Based Recipes from Ethiopia to Senegal by Marie Kacouchia © Éditions La Plage, 2021. Translation © The Experiment, 2022. Reprinted by permission of the publisher.

Pulling greenhouse gases out of water is an odd-sounding idea, but the oceans are the planet's number one carbon sink, and direct air carbon capture has pretty serious problems: it costs a lot, and uses a lot of energy. According to IEA figures from 2022, even the more efficient air capture technologies require about 6.6 gigajoules of energy, or 1.83 megawatt-hours per ton of carbon dioxide captured.

Most of that energy isn't used to directly separate the CO2 from the air, it's in heat energy to keep the absorbers at operating temperatures, or electrical energy used to compress large amounts of air to the point where the capture operation can be done efficiently. But either way, the costs are out of control, with 2030 price estimates per ton ranging between US$300-$1,000. According to Statista, there's not a nation on Earth currently willing to tax carbon emitters even half of the lower estimate; first-placed Uruguay taxes it at US$137/ton. Direct air capture is not going to work as a business unless its costs come way down.

It turns out there's another option: seawater. As atmospheric carbon concentrations rise, carbon dioxide begins to dissolve into seawater. The ocean currently soaks up some 30-40% of all humanity's annual carbon emissions, and maintains a constant free exchange with the air. Suck the carbon out of the seawater, and it'll suck more out of the air to re-balance the concentrations. Best of all, the concentration of carbon dioxide in seawater is more than 100 times greater than in air.

Previous research teams have managed to release CO2 from seawater and capture it, but their methods have required expensive membranes and a constant supply of chemicals to keep the reactions going. MIT's team, on the other hand, has announced the successful testing of a system that uses neither, and requires vastly less energy than air capture methods.

In the new system, seawater is passed through two chambers. The first uses reactive electrodes to release protons into the seawater, which acidifies the water, turning dissolved inorganic bicarbonates into carbon dioxide gas, which bubbles out and is collected using a vacuum. Then the water's pushed through to a second set of cells with a reversed voltage, calling those protons back in and turning the acidic water back to alkaline before releasing it back into the sea. Periodically, when the active electrode is depleted of protons, the polarity of the voltage is reversed, and the same reaction continues with water flowing in the opposite direction.

In a new study published in the peer-reviewed journal Energy & Environmental Science, the team says its technique requires an energy input of 122 kJ/mol, equating by our math to 0.77 mWh per ton. And the team is confident it can do even better: "Though our base energy consumption of 122 kJ/mol-CO2 is a record-low," reads the study, "it may still be substantially decreased towards the thermodynamic limit of 32 kJ/mol-CO2."

The team projects an optimized cost around US$56 per ton of CO2 captured – although it's not fair to compare that directly against full-system direct air capture costs. The study cautions that this does not include vacuum degassing, filtration and "auxiliary costs outside of the electrochemical system" – analyses of which will have to be done separately. Some of these, however, could potentially be mitigated by integrating the carbon capture units in with other facilities, for example desalination plants, which are already processing large volumes of seawater.

There are some other benefits too; increased carbon buildup in the ocean over recent years has already caused problems with acidification, threatening coral reefs and shellfish. The alkaline output of this process, if directed where it's needed, could help redress the balance.

The team has a practical demonstration project planned for sometime in the next two years, and says there are plenty of things that still need work. For one, the researchers would love to be able to separate the gas out without a vacuum system. And mineral precipitates are fouling the electrodes on the alkalinization side, so there's plenty of progress yet to be made.

The study is open access in the journal Energy & Environmental Science.

Source: MIT

In a small windowless room on a sweltering summer’s day, I find myself face-to-face with an entomological rock star. I’m at the University of Lincoln in eastern England, inside an insectary, a room lined with tanks and jars containing plastic plants and dozing insects. Before I know it, I’m being introduced to a vibrant-green katydid from Colombia.

“Meet Copiphora gorgonensis,” says Fernando Montealegre-Z, discoverer of this six-legged celebrity. The name’s familiar: It’s been splashed across the world alongside photos of the insect’s golden face and miniature unicorn’s horn. The renown of this katydid rests not on its looks, though, but on its hearing. Montealegre-Z’s meticulous studies of the magnificent insect revealed that it has ears uncannily like ours, with entomological versions of eardrums, ossicles and cochleas to help it pick up and analyze sounds.

Katydids — there are thousands of species — have the smallest ears of any animal, one on each front leg just below the “knee.” But their small size and seemingly strange location belie the sophisticated structure and impressive capabilities of these organs: to detect the ultrasonic clicks of hunting bats, pick out the signature songs of prospective mates, and home in on dinner. One Australian katydid has capitalized on its auditory prowess to capture prey in a very devious way: It lures male cicadas within striking distance by mimicking the female part of the cicada mating duet — a trick requiring it to recognize complex patterns of sound and precisely when to chip in.

Awesome? Absolutely. Unexpected? That, too. I’d never given much thought to insect ears until now. Insect eyes and antennae stand out, but ears? Even the eagle-eyed could be forgiven for wondering if insects have them. Yet obviously, some must hear: The summer air is filled with the trills, chirps and clicks of lovelorn crickets and grasshoppers, cicadas and katydids, all trying to attract a mate.    

Curiosity piqued, I call neurobiologist Martin Göpfert at the University of Göttingen in Germany, who studies hearing in the fruit fly Drosophila melanogaster. Amazing though katydid ears are, he tells me, they’re just one of many with astonishing capabilities: Evolution has made so many attempts at shaping ears, the result is a huge diversity of structures and mechanisms. Most are hard to spot, if not invisible, and in many cases insects produce and sense sounds so far beyond our own range that we overlooked their abilities entirely. But with the advent of new tools and technologies, ever more examples are coming to light.

Sensory biologists, acoustics experts and geneticists are working together to pin down how they all work, how and when they evolved, and why. And thanks to some of this newfound knowledge, and an assortment of fossil insects, there’s even the tantalizing prospect of being able to eavesdrop on the ancient past, adding a new dimension to our understanding of the life and times of some long-vanished animals.      

When insects first appeared some 400 million years ago, they were deaf, Göpfert tells me. These ancestral insects went on to diversify into more than 900,000 species, and while most remain as deaf as their ancestors, some gained the means to hear. Of the 30 major insect orders, nine (at last count) include some that hear, and hearing has evolved more than once in some orders — at least six times among butterflies and moths. The 350,000 species of that most dazzlingly diverse group, the beetles, are almost all deaf, yet the few that have ears acquired them through two separate lines of evolution. All told, insect ears arose more than 20 separate times, a sure-fire recipe for variety.

Ear, there and everywhere

Location is the most obvious difference between one insect’s ears and another’s: There are ears on antennae (mosquitoes and fruit flies), forelegs (crickets and katydids), wings (lacewings), abdomen (cicadas, grasshoppers and locusts) and on what passes for a “neck” (parasitic flies). Among moths and butterflies, ears crop up practically anywhere, even on mouthparts. The bladder grasshopper has an abundance of ears with six pairs along the sides of its abdomen. Praying mantises have a single, “cyclopean” ear in the middle of their chest.

This anywhere-goes approach might seem a little weird but there’s a simple explanation: In every case where an insect ear evolved, the starting point was an existing sensory organ: a stretch detector that monitors tiny vibrations when neighboring body segments move. Those detectors occur throughout the insect body but evolution typically only modified a single pair — apparently, almost any pair — to perceive the airborne vibrations generated by sound.

From there on, each new attempt to forge ears went even further in its own direction as other structures were co-opted and reconfigured to capture, amplify and filter sound, extract the relevant information and convey it to the nervous system. In mosquitoes and fruit flies, sound causes fine antennal hairs to quiver. Most other hearing insects have “eardrums”: thin, membranous patches of exoskeleton that vibrate when sound waves hit. Some eardrums are backed by air-filled acoustic chambers, others by fluid-filled ones. The number and arrangement of sensory cells that detect and decode those vibrations — and the neurons that send the signals to the brain — also vary from ear to ear. So while some moth ears function with just one or two neurons (making moths the most rapid responders), a male mosquito’s ear has around 15,000 (making it exquisitely sensitive).

Some ears are relatively simple; others have extra bells and whistles linked to their lifestyle. Take the parasitic fly Ormia ochracea, which deposits its larvae on a particular species of cricket after identifying and locating it from its characteristic call. The fly’s ears sit side by side on its “neck” and are theoretically too close together to pinpoint its target. Yet they take the prize for accurate location, thanks to an elastic band connecting the eardrums so they rock up and down like a seesaw, ensuring sound hits one ear fractionally later than the other.

Katydid ears, as so neatly demonstrated by Montealegre-Z and his colleagues, are unique both in their complexity and their similarity to a mammal’s. Using a micro-CT scanner, the scientists reconstructed the insect’s entire hearing system, discovering two previously unknown organs in the process. The first is a small, hard plate behind the eardrums; the second, a fluid-filled tube containing a line of sensory cells. Through painstaking investigation that included shining lasers at the eardrum and recording the light bouncing back, the team showed that the small plate transmits vibrations in the insect’s eardrum to the fluid in the tube — the same role played by the bones in our middle ear. The signal then travels in a wave along the tube and over sensory cells tuned to different frequencies — making this organ a miniature, uncoiled version of our own, snail-shaped cochlea.    

The team has now gone on to show why female katydids are so good at finding a mate in the dark, even though their ears are close together (not so close as those of the parasitic Ormia, but near enough to make pinpointing sound a sizeable challenge). Our own ears lie on either side of our (large) heads and are far enough apart for a sound to reach them at different-enough times and loudness for the brain to compute and locate the source.

Katydids solved the problem (again, in a unique way) by enlarging a breathing tube that runs from a pore in the side of the chest to the knee; sound reaches the eardrums both from outside the body and from the inside via the tube. Montealegre-Z and his colleagues showed that sound travels this inner, back route more slowly — so each sound hits the eardrum twice, but at slightly different times, dramatically improving the insect’s ability to locate the source.

The katydid’s remarkable ears haven’t yet given up all their secrets, and Montealegre-Z’s team is now trying to pin down how the receptors in the insect version of the cochlea pick out different frequencies. The star of this study is Phlugis poecila, a “crystal” katydid named for its transparent outer cuticle, a feature that allows the team to record and measure processes as they happen. “We’ll be able to watch hearing at work and see processes never seen before,” Montealegre-Z says.     

If how insects hear varies enormously, so does what they hear. Mosquito ears are good for maybe a meter; the many-eared bladder grasshopper can hear from a kilometer or more away. Cricket ears detect low frequencies; mantis and moth ears are tuned to ultrasound, way beyond anything humans (or their dogs) can hear. Still others, such as a katydid’s, have broadband hearing. “Insects only hear what they need to hear,” says Göpfert. “And evolution provided what was necessary.”

But what drove evolution to turn stretch receptors into ears in the first place, and so bring sound to the insect world? That’s a question still on many entomologists’ minds. A reasonable guide is how insects use their ears today, but it’s only a guide, since an ear originally acquired for one purpose might easily have been co-opted over the eons to serve another. One thing’s certain: As biologists investigate more insect groups in greater detail, some long-held notions may bite the dust.    

An ear for danger

In modern insects, one of the primary functions of ears is to hear the approach of a predator in time to take action and avoid it. For night-flying insects, the greatest threat comes from insectivorous bats that detect and track prey with ultrasonic sonar, and so their hearing is tuned to the frequencies of the bats’ echolocating clicks. The insects then respond with characteristic moves to escape the sonar beam: sharp turns, loop-the loops, air-to-ground power dives. Certain tiger moths even jam the bat sonar with clicks of their own. Experiments have shown that bat-detecting ears dramatically improve an insect’s prospects of surviving attack: In one study, mantises escaped 76 percent of bat attacks, but that number fell to 34 percent when they were deafened.

If predation is a powerful driver of evolution, so, too, is sex. And sound is an efficient way for an insect to identify itself to prospective mates: Sound travels well, works in the dark and provides the means to develop signature songs and private communications that no one else can hear. 

So, successful sex or survival? Which lies behind whose ears?

In some cases, researchers are reasonably sure. Cicadas seem to have evolved hearing for mating purposes: Only singing species have ears and they are sensitive only to their own low-pitched songs. For moths, bats were the trigger. Lepidoptera have been around some 150 million years, yet no moths had ears before echolocating bats arrived on the scene about 60 million years ago. And many of the eared moths are sensitive only to the frequencies employed by their local bats — strong evidence that the ears evolved as bat detectors.

What, though, to make of the mantis, owner of the cyclopean ear? Today, mantises seem to use their ears exclusively as bat detectors. But entomologists now have vast amounts of data on the varied anatomy of mantis ears and an accurate DNA-based mantis family tree, from which they traced the original mantis ear. It belonged to a species that lived 120 million years ago, rather earlier than those sonar-guided bats. There’s growing evidence that predators other than bats might have spurred the evolution of their ears and those of some other insects — perhaps reptiles, or birds, or early mammals. Animals moving through the undergrowth, pattering over rocks or landing on a leafy branch are rarely silent. The noises they make include audible and ultrasonic elements.

Flying birds, which have existed for 150 million years, are increasingly seen as contenders. In groundbreaking research, Canadian biologists recorded sounds generated by the beating wings of chickadees and eastern phoebes as they moved in on insect prey, and found that the wing beats included a wide range of frequencies that insects can detect, from low-pitched sounds audible to cicadas, butterflies and grasshoppers, to ultrasonic sounds picked out by moths and mantises.         

And what of the katydids, possessors of the most ancient ears of all? Modern katydids use their ears both in communication and as bat detectors. But the katydid sound-producing apparatus can be traced back through the fossil record to an early type of ancestor that lived 250 million years ago, well before bats did. So the prevailing theory up till now has been that the evolution of katydid ears took some turns. The ears’ initial function was to enable katydids to hear one another, and later on, the thinking goes, those ears were co-opted to serve as bat detectors. This led to the extension of their hearing from the audible range (below 20 kHz) to the ultrasonic (beyond the reach of human ears) — and that, in turn, allowed evolution of the more complex, higher-pitched songs that katydids exhibit today. Today, only a minority of katydids sing in the audible range, while about 70 percent have ultrasonic songs and a few have extraordinarily high-pitched songs. The record holder, so far, is the recently discovered Supersonus aequoreus, which calls at an astonishing 150 kHz.

But is that story right? To get at the answer, scientists needed to know what katydids were hearing in the distant past, and that meant taking a close look at katydid fossils. The fossilized ears are not themselves very informative: They are rare and their structure hard to make out. But there’s another way of getting at hearing: from the detailed anatomy of the sound-producing file-and-scraper apparatus on fossilized katydid wings. “Those structures are much larger and clearer, and we can use them to recreate the sound they made very accurately,” says Montealegre-Z — and from that, infer what katydids must have heard.

Blast from the past

In 2012, Montealegre-Z and fellow bioacoustics expert Daniel Robert at the University of Bristol made headlines when they used this approach to reconstruct the song of a katydid from Jurassic times, a sound unheard for 165 million years. What made that possible was the discovery of a Chinese fossil katydid with almost perfectly preserved wings. Archaboilus musicus, as the extinct insect has been named, would have “sung” musical songs at frequencies around 6.4 kHz, sounding more like a cricket than a modern katydid. That fits nicely with the story that katydids first evolved hearing to communicate. 

Since then, though, the team has been studying more fossil katydids, and what they are finding suggests that the theory might need an overhaul. It seems that some ancient katydids were using ultrasound long before bats existed, says Montealegre-Z. Katydids also hear a much wider range of frequencies than they’d need just to hear themselves. To his mind, this suggests that their ears first evolved not for singing but, much like mantises, for self-preservation. “I think their ears evolved to hear predators,” he tells me. “Predators make a diversity of sounds and so ears must be able to pick them out.”

If studies like these are helping to unravel the evolutionary history of insect hearing, they also promise something more: the opportunity to eavesdrop on the ancient past and gain new insights into insect behavior. They’ve also made me impatient for next summer and the chance to explore the rich insect life of the gently rolling chalk hills hereabouts with new eyes — and ears, especially ears.

In summer, the air over the Sussex Downs is alive with a symphony of insect sound as grasshoppers and katydids chirp, buzz and click in their quest for love. If I strain my ears to the limit, I might be able to pick out the sewing-machine rattle of a great green katydid or the soft hissing song of a conehead, and if I’m very lucky, perhaps even the rapid-fire clicks of the wart-biter, the UK’s rarest katydid. But how much more will I be missing? I’d give a lot to have ears that can pick out the songs and sounds scientists are piecing together, but that insects alone can hear.