Sleeping with the enemy

Humanity hates nothing more than an insect that bites. But the dreaded bed bug keeps finding novel ways to fight back against our assaults.

Illustration by Arpita Choudhury

Illustration by Arpita Choudhury

Peering at the fig jam-coloured oval-shaped specks in their partially sealed containers, I couldn't help but stifle a chortle at having once been frightened by them — a fright so gripping that I devoted a week's worth of my allowance to buy a magnifying glass at my local stationery store when I was seven, just so I could unmask the bandits I was sure were giving me dime-sized itchy welts across my arms and legs that summer.

Bed bugs.

The flattened bugs lazily reclined in their 12 makeshift domiciles, paying no mind to me visiting Rutgers University's Department of Entomology. The little movement I noticed came from a slightly smaller specimen in one of the emptier jars, possibly going through the last of the insect's five nymphal stages, as it momentarily tried to shimmy up the accordion-folded piece of paper stacked horizontally in each one, but even that might have been a mirage.

"We like to keep it interesting for them," explained Dr Changlu Wang, an urban pest researcher and head of his own namesake lab at the university, with soft-spoken sincerity as he pulled the jars out from their dark and presumingly warm storage space.

I had made my way to Wang's lab on a scorching August Friday morning to better know my one-time foe, but I was far from the only one with a piqued interest in them. Bed bugs, and the winding evolutionary journey they've made since they first shacked up with our hominid ancestors, are fast becoming the talk of the town. Unfortunately, it's because they've stepped out of the shadows of our childhood fears and once again become a near-universal pest since the turn of the millennium.

 
Bed bugs aren't the cutest critters out there, let's be honest. Gilles San Martin/Flickr (CC BY-SA 2.0)

Bed bugs aren't the cutest critters out there, let's be honest. Gilles San Martin/Flickr (CC BY-SA 2.0)

 

The prevailing theory of how the common bed bug, or Cimex lectularius, became common goes back to at least the earliest days of modern humanity, that distinct split in the evolutionary branch when Homo sapiens first appeared on the world stage, roughly 200,000 years ago in Africa. The actual species predates us though — 250,000 years at least, but likely even older, according to Dr. Warren Booth, an evolutionary biologist at the University of Tulsa. 

In either case, back then bed bugs were cave bugs, already having shed their capacity to fly and serving as the crawling, blood-feeding pests of bats (much like our tailbones, though, the vestigial trace of their wings can still be seen even today). The research of Booth and others indicates that a population of humans in Europe or possibly the Middle East sought out the warmth of these caves only to come across a population of bat bugs that mosied on over and took a keen liking to our blood. It’s also possible that our hominid relatives may have first picked up the bugs and then given them to us. Whether this chance encounter, which may have originally occurred some 225,000 years ago, was an isolated event or repeated itself numerous times is still unknown, though Booth’s money is on the latter. 

Eventually, this subset of bugs became uniquely tethered to us, and their innate traits morphed to suit their new hosts, especially as we began to establish permanent settlements and resting places. As Brooke Borel details in her recent charming biography of the bed bug, Infested: How The Bed Bug Infiltrated Our Bedrooms And Took Over The World, human bed bugs became nocturnal to suit our sleeping schedules; their mouthparts through which they slurp up our blood expanded and became longer to accommodate our wider blood cells and better pierce our skin, respectively; their legs became sleeker to run away from us faster (faster by bed bug standards at least) and the hairs along their body shortened to make climbing the surfaces of our homes and hotels easier. Importantly, they also became specially tuned to our pheromones, which when combined with the carbon dioxide we regularly exhale, turned napping humans into an easy target. 

Vision and touch also play a key role in their survival, Wang and others have found. Bed bugs gravitate towards darker colors like black and red, colors more likely to represent safe haven, and their admittedly low-resolution sight can still tell apart the height of objects to a certain degree, perhaps aiding them in finding their way up our bedposts. And they prefer to walk on coarse but not too coarse surfaces, a trait that many past and present pest control experts — Wang included — have tried to exploit by crafting enticing traps that can entangle the bed bugs as they walk on through. Go one level deeper and you’ll find the bed bug has its own codependent relationship with a parasitic genus of bacteria called Wolbachia. Unlike many of the other insects Wolbachia infects, however, bed bugs have plenty to gain from the transaction. In exchange for a cozy place to stay, Wolbachia supplies the bug with much needed vitamin B.

The fact that males court females by stabbing their penises in her abdomen, though? That’s a squicky trait that belongs to all the member species of the parasitic Cimicidae family, most of which, like human bed bugs and bat bugs, tend to stick to their specialised host of choice.

 
We're only a recent host for bed bugs — before us, they happily feasted on the blood bats. AlphaLu/Flickr (CC BY-NC 2.0)

We're only a recent host for bed bugs — before us, they happily feasted on the blood bats. AlphaLu/Flickr (CC BY-NC 2.0)

 

For all these adaptations, though, the bed bug was seemingly wiped off the face of the earth starting in the 1940s, thanks mostly to the widespread development and deployment of incredibly effective insecticides like dichlorodiphenyltrichloroethane (more commonly known as DDT). For a brief moment in history, DDT and similar products allowed us to think we had bested the insect once and for all. Bed bug eradication was hardly the primary goal as we dusted DDT across the globe for several decades —  that was reserved for mosquitoes and agricultural pests — but it sure was a nice perk. By the 1970s, though, scientists and the public worried about the broader impact of DDT on the surrounding wildlife, namely birds, and countries like the U.S. banned the chemical from being used within its borders (DDT is still used in some areas of the world today, but in a limited fashion and largely only for mosquito control). Other less toxic classes of insecticide, like pyrethroids (synthesised from the naturally occurring pyrethrins), became the standard and oftentimes only legal chemical of choice for household use.

Unbeknownst to most of us, save for some prescient scientists, was that insects were steadily gaining resistance to these chemical weapons — even the mythical DDT — this whole time. If anything, DDT only prepared the critters for the advent of pyrethroids, since they kill in a similar fashion. The chemicals overwhelm insects by stapling open the voltage-gated sodium channels found in their nerve cells, causing the cells to ceaselessly fire and leading to paralysis, convulsions, and ultimately death for their owner.

But as potent as these chemicals were, it was equally, and elegantly, simple to beat them. In the case of the bed bug, it largely took one or two precise mutations in the gene that regulates the molecular receptors found in sodium channels. Known as knockdown mutations, they’re the genetic equivalent of changing your Netflix password by swapping out one letter with another so your ex can’t watch the next season of Stranger Things on your account. Today, close to 90% of tested bed bug populations have at least one of these mutations, and nearly 50% have both. 

But the bed bug has other tricks up its chitinous sleeves. Compared to their vulnerable counterparts of the past, modern bugs literally have thicker skin, by which I mean a thicker cuticle, the term for its tough fingernail-like exoskeleton. While this added armour functions as a hardier physical barrier against insecticides, there’s even more going on. Most of the other resistance genes expressed by bed bugs are found in the cuticle, a trait unique to the species. These include genes that produce detoxifying enzymes and protein pumps that transport away toxins before they can cause harm. Only if the insecticide can make it through this gauntlet will they reach the bug’s nervous system, where they’ll still have to contend with the knockdown mutations. These latter mechanisms of resistance are particularly troubling for the future of bed bug control. While the knockdown mutations are keyed to pyrethroid and DDT resistance specifically, the other mechanisms aren’t, and there’s already evidence the bugs are using them to evade the next generation of insecticides, called neonicotinoids.

Say what you will about them, the bed bug is nothing if not a worthy adversary.

DDT was a very common ingredient even in domestic insecticides in the 1940s and 1950s, and bed bugs quickly became resistant. Kevin Krejci/Flickr (CC BY 2.0)

DDT was a very common ingredient even in domestic insecticides in the 1940s and 1950s, and bed bugs quickly became resistant. Kevin Krejci/Flickr (CC BY 2.0)

Though we’re still not sure exactly when and where the bed bug resurgence first broke through, it likely began in earnest sometimes around the early 2000s, aided not only by increased resistance but greater global travel as well. 

That would have made my encounter with them in the summer of 1996 an early skirmish, the bed bugs having retreated to poorer areas of the world, and to Brooklyn, New York, where they wouldn’t be relentlessly pursued and could steadily build up their strength again. Bed bugs, like many pests, have long been considered a problem of the poor, which is only half right — bugs aren’t swayed by nationality or income, but poorer neighborhoods are less able to devote the resources, which include chemical and non-chemical approaches, needed to control them. Being the second-generation son of an Ecuadorian family who lived in a very modest and cramped apartment, I was a juicy target for the bugs, or chinches as they’ve called in my native Spanish tongue. 

Or least I would have been, had, as I embarrassingly learned a week later after visiting Rutgers, actually been bitten by them. 

“No, we never had them!” exclaimed my bemused mother at dinner, as she began to recite the laundry list of extended family members who had. A great aunt there, an older sister after she left the home here, but not us. One story in particular, of a young cousin who marched back and forth to the doctor’s office after an especially nasty series of rashes that refused to clear up and were eventually diagnosed as bed bug bites, felt all too familiar. Near as I can tell, the magnifying glass hunt certainly happened, but my recollection of having pleaded for my mother’s attention, the doctor’s visits, the handsomely paid but still effective exterminator, and spending weeks tugging loads of steam-pressed laundry had all been lifted from my cousin’s account. I had been a plagiariser for years worth of late-night bar sessions and didn’t even know it. 

I wonder if there’s a hallmark card for that sort of faux pas.

Even if my own bed bug tale turned out to be nothing more than pilfered fantasy, though, the story of the bed bug is far from over. Specialised as common bed bugs are, they’re not a completely genetically distinct species from the bugs that infest many species of bat. Bat and bed bugs can still feed from the other’s hosts and can even breed with one another, though not as effectively as they can with their respective clans. Booth’s research suggests that this divide has been widening since bed bugs first hitched a ride onto humanity and may someday lead to a definitive fork in the road. Our ongoing arms race against them has certainly sped things along — bat bugs don’t have the resistance genes of their human counterparts — but for now, the bug’s evolutionary path is unchartered.

Cringe and stress-inducing as bed bugs are (though not disease-causing, thankfully), there’s something eerily poetic about their unwittingly intimate relationship with us. Hundreds of thousands of years before people thought to receive salvation by drinking the metaphorical blood of Christ, bed bugs had used ours to nourish themselves and accomplish ecological success on a global scale. And even when we had seemingly pushed them to the brink of destruction, they fought back and trounced us within the span of a few decades. Somehow, I doubt the next generation of pest control methods will do much better than earn us a tenuous truce, and who’s to say they won’t outwit us again? 

It’s been hard not to walk away with a begrudging respect and admiration for the bed bug. That and a deep-seated paranoia about every new bed or couch I spend my time on for the rest of my life.

Edited by Jack Scanlan