Sex, Interrupted: How Humans Are Disturbing Animal Reproduction

Inspired by a lonely glowworm, a British zoologist investigates how humans are disturbing mating rituals of the natural world.

By Jules Howard
Oct 2, 2014 6:00 PMNov 12, 2019 6:23 AM
Jonathan Bartlett


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This is not only about how boy meets girl; it’s also about how boy flies straight past girl and chooses instead to try to have sex with a lamppost.

It’s 10:05 p.m. I am sitting on the curb in a pub car park. Many guided nature walks start this way. Wildlife groups think it’s so easy when they organize guided walks for the public. “Meet at the Robin Hood pub car park!” they say in their ads. “10 p.m.!” Well, that’s all well and good, but it’s dark at 10:05 p.m. and I feel a bit weird wandering up to people outside a pub, bumbling about like Hugh Grant, asking strangers, “Excuse me, are you guys here for the glowworms?” Then I notice them: about 30 people standing in the street opposite, all of whom are wearing good, sturdy walking boots.

David Seilly, our glowworm expert and guide, is addressing the crowd. Already he weathers a polite rain of questions from the other attendees. “How many might we see?” “Will I need my waterproofs?” “Will there be toilets?” The usual.

I have never seen glowworms before. The thought of seeing even one excites me, though. I love what they stand for: an animal that throws caution to the wind, screaming not through feathers, or through squawks, songs or dances, but through the medium of photons pumped out of its backside. “Come to the light, baby,” she says gently to the males. “Come to momma.”

Off we go to our venue for the night, Cherry Hinton Chalk Pit. The former quarry provided hard chalk to build the colleges of Cambridge University up the road and lime for the cement.

After we move through the gates, David, our expert, stops. We form a compact circle around him. The summer sun has been down for almost an hour, and we are almost totally invisible to one another. Our eyes adjust to the restricted wavelengths.

Jonathan Bartlett

“Excuse me,” says a quiet voice to my right. “But what is a glowworm?” “The glowworm is a beetle,” responds our sage. “We’ve only got one species in Britain. They belong to the firefly family. This one’s strategy is rather simple: Large flightless females emit light with the aim of attracting males.”

“So, shall we go and see some?”

I had imagined that the next bit would take some time. That, like all good nature-writing stories, we would search and search and then search some more, and then, just as we were packing up, we’d see one: glowing like a beacon, a single revolutionary invertebrate in a world lit by artificial coal-fired lights. Our glowworm. We’d whoop for joy, hug, weep with the wonder of it all. But no, it wasn’t quite like that.

It happened like this: We turned a corner, looked at the first long bank of vegetation and saw them, five or six twinkling stars in the grass. And that’s the first thing you need to know about looking for glowworms — it’s remarkably easy. Look for little points of light, then, well . . . walk toward them.

Within what seems like seconds, small clusters of five or six people bend over each ghostly green point of light. I head toward the nearest. Someone shines a flashlight right into the beetle’s appendage-laden face. Even with the full beam on her, the glowworm continues pumping out her green charge, illuminating the strands of birdsfoot treefoil on which she clings. She is like an elongated woodlouse, and about three times the size. Her tapering tail is waggled over to one side, and it is from the final three segments that the ghostly glow emanates.

We amble in our own little clusters from this point on, homing in on more tiny, glowing, green bottoms among the undergrowth.

“And were they once everywhere in Britain?” asks someone to my left. David chews on this for a second. “Yes . . . they were once probably everywhere,” he says, before mulling over a thought in his head. “I’d quite like to contemplate the impact on male glowworms of all of the streetlights,” he adds quietly, looking at the reflected streetlights bouncing back off the clouds above. Those who heard him say it stand silent there, thinking about this for a few seconds. “Streetlights?” someone from behind me says.

“The trouble is, the males probably go and mate with the streetlights rather than mate with the females.” They do what? “Is that why they’re declining?” someone asks to my right. “Well, it might be,” offers David.

I stood there and imagined what a streetlight must look like to a male glowworm. Impossibly long strip, sultry red tone, that irresistible sexy hum. The males drawn in on tractor beams, flying straight past the females. I picture their final hours, bashing-bashing-bashing against a panel of illuminated glass until they expire or succumb to a passing bat. Poor little suckers. It was the first time I had ever really consciously imagined that human actions, human insight, human ingenuity, human technology, could mess up the sex life of another animal. Are we civilized folks becoming nature’s cold shower? Predictably, the answer is yes. And not only are some aspects of nature’s sex taking a battering; in some cases, it might actually be fighting back, modifying its advertising to be better heard over humanity’s din.

Nature Fights Back

Roads are one such battleground. It appears that here, natural selection is working at a rapid rate. And beside these roads, grasshoppers are becoming the study species of choice. At least some are adapting to the ruckus.

Grasshoppers make their calls by scraping rows of tiny pegs on their back legs against a thickened vein on the forewing. Each grasshopper species has its own call, simply determined by the number of tiny pegs and the rate of this “stridulation.” Because grasshoppers often share habitats with a number of other grasshopper species, natural selection has driven each to stand out from the others when calling. When comparing populations of bow-winged grasshoppers from locations near busy roads with those away from roads, some German scientists in 2012 spotted a few key differences. They found that some grasshoppers from noisy habitats try to boost the low-frequency parts of their song to get their voices better heard against the low-frequency drone of traffic. Nature is fighting back, and the low frequencies are the battle lines. In fact, the low-frequency parts of other animal songs appear to be similarly vulnerable to the blaring noise of road traffic. In early 2013, a Canadian study showed that the presence of lower-frequency elements in a song could be used to predict, to a degree, the abundance of songbirds setting up shop near a road. In human terms, it seems that low-frequency singers lose patience with roads and think, “Screw this: I’m off to somewhere quieter.” 

Jonathan Bartlett

Such results are fascinating, not least because they highlight how animals like songbirds may be unconsciously calculating the effectiveness of their efforts, and looking for the best time, and the best place, to let rip with a song. (Some research suggests that this is one reason why birds sing first thing in the morning — after all, sound travels farther on a cool morning.)

Similar studies have been undertaken comparing noisy and non-noisy habitats and looking at the birds that sing there. They hint at the same thing: Lower-frequency sex songs are being drowned out by the human din. In the Netherlands it’s observable in great tits, many of which have more high-pitched songs in towns and cities than their countryside neighbors. In Germany, it’s the nightingales. They sing up to 14 decibels louder nearer to roads than in nearby forests. And San Francisco’s sparrows are also more chirpy than they once were, particularly in the higher registers. Here, three “dialects” once flourished among sparrows. Now only one dominates: the most shrill and easy to hear over the rumble of traffic.

Animals are adapting, and relatively quickly. What’s unclear at the moment is how exactly they manage this. It could be that, somehow, they are listening and responding to the surrounding lower-level frequencies. Or it could be that a genetic shift in song behavior is occurring within the gene pool, since some of the population aren’t heard and simply die off unmated, their genes lost. Either way, the dawn chorus is losing its tenors.

Though less about it is understood, another place where the chorus may be changing is underwater. Here, a host of animals, including fish, whales, dolphins and even invertebrates, depend on sound. Some use it for hunting, others to detect predators or prey, but many use it for sex. It may be that they are being drowned out, too. Sure, cars are noisy, but have you ever heard the racket an oil-company ship makes, one towing air guns that fire fusillades loud enough to detect the bounce-backs of oil reserves under the rocks? No, neither have I, but I suspect Flipper could tell us more if we taught him the sign for “THAT IS A VERY LOUD NOISE MAKE IT STOP.” The same goes for those undersea construction operations that drive piles into the seafloor, which they then explode. These noises travel for hundreds of miles, perhaps more. To sea creatures, we may be the neighbors from hell.

What most concerns some people, though, is the rapidness of the increase in sea noise: In some places there may have been a hundredfold increase in such noise since the 1960s alone. Mind-boggling, really. And worrying. Whales and dolphins could provide a useful model for research into such impacts, largely because their sounds are relatively easy to study: They are among the loudest noises any animal has ever made, reaching as much as 188 decibels in the blue whale. (That’s only a little less loud than strapping a grenade to your head and pulling the pin.) These calls can travel more than 600 miles, which is equivalent to the blue whale hanging from the ceiling at the Natural History Museum in London having a chat with the model blue whale in the Natural History Museum in Gothenburg, Sweden.

The purpose of these calls is still being debated. They are likely to communicate a number of pieces of information, including species, activities, location, social calls and, of course, sexiness. Could the calls be affected by ocean noise? The jury is still out, but it’s becoming a hotly debated topic. Many agree that increasing ocean noise is likely to be affecting their lives and loves, at least a little. For some species it might mean nothing; they just shout louder. But for others? It’s an area of research that might provide fascinating insights in the next few years.

Lights Out

So what of streetlights? It’s well known that moths die through attraction to artificial lights (though the impact this has on populations as a whole is unknown). If serious and true, a decline in moths could have an impact on the sex lives of plants that flower only at nighttime. If the moths are too busy hanging around the lights and not pollinating the flowers, it might be lights out for both, evolutionarily speaking. (Moths have far bigger problems than this though, of course — habitat loss and fragmentation being key issues.)

Though it’s unlikely that they kill off whole populations, streetlights undoubtedly have the power to change invertebrate communities, possibly some even for the better.

Research suggests that the ground beneath a newly installed streetlight can become an attractive place for predators and scavenging invertebrates like ants, harvestmen, amphipods and ground beetles — plenty of food and, perhaps, plenty of sex for some as a result. But, as in the seas, it’s early days; there is much more research to be done, and maybe such concern is overstated. What’s surprising is that, as with marine life, so little research is being done on the impact to invertebrates that night-lights might have. After all, it’s estimated that the use of artificial lights increases at a rate of 6 percent globally each year. Might this be something we regret not studying sooner? My point is that these are known unknowns, as Donald Rumsfeld once said, and I hope that one day they will become fully fledged “knowns.”

But I digress. It’s time to get back to those glowworms.

I check my watch: 12:30 a.m. Time to leave Cherry Hinton Chalk Pit and get on the road back home and to bed.

It’s 1 a.m. by the time I pull out of the pub car park. I’m tired. It’s time for home. The road that should take me home, the A14, is closed, so I detour through the minor roads.

I smash through hundreds of moths on that tiresome journey home, some as big as ghostly bats, some little more than whirling bits of belly-button lint. They waft up in front of my headlights like steam off the road. Dozens of them, bashing into my bumper or hammering against the side mirrors. Some ricochet, or sound as if they might chip the glass. I wince each time, guilty for their stolen sex.

From the forthcoming book "Sex on Earth: A Celebration of Animal Reproduction" by Jules Howard, to be published by Bloomsbury. Copyright © 2014 by Jules Howard. Printed with permission.

[This article originally appeared in print as "Caught in the Act."]

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