Cimex lectularius, the common bedbug, was so thoroughly beaten back in American and European homes by the early 1950s that entomologists at the time openly wondered whether the species was on its way to becoming a rarity in developed countries. The insect had lived on human blood since at least the Bronze Age, but a decade of DDT spraying after World War II collapsed infestations to the point where a young pest-control worker in London or Chicago could go an entire career without seeing one. Then, starting in the late 1990s, the bugs came back — and the reason, traced through the genomes of the survivors, is that the descendants of the few bedbugs that lived through the DDT era carry mutations that make modern pyrethroid sprays roll off them like water.
The story of that comeback is one of the cleanest examples of evolution-in-action ever documented in an urban pest.
The vanishing act of the 1950s
Before the war, bedbugs were a routine misery. British surveys from the 1930s found infestations in roughly a third of working-class housing in some London boroughs. American tenement inspectors reported the same. The bugs hid in mattress seams, in cracks behind wallpaper, in the frames of iron beds, and they fed at night with a bite most people didn’t feel until the welts came up hours later.
DDT changed that almost overnight. Cheap, persistent, and lethal to a broad spread of insects, it was sprayed directly onto bed frames, baseboards, and mattress ticking through the late 1940s and into the 1950s. By 1960, entomology textbooks were describing bedbugs in the past tense in most of the developed world. The bugs held on in parts of Africa, South Asia, and eastern Europe, but in New York, London, Paris, and Sydney they had effectively vanished from ordinary homes.
That collapse is what makes the return so striking. For roughly forty years, two full human generations grew up without ever encountering the insect their grandparents had spent lifetimes battling. Pest-control companies stopped training staff to identify them. Hotel housekeeping manuals dropped the section. The knowledge quietly aged out of the industry.
The comeback, dated to the late 1990s
Reports of bedbug infestations began climbing in the United States, Australia, and western Europe around 1997 and 1998. By the mid-2000s the increase was steep enough that public-health agencies were tracking it. Pest controllers reported a surge across multiple cities. Paris made international news in September 2023 when infestations turned up in Métro carriages, cinemas, and the Charles de Gaulle Airport, prompting a government task force and a wave of coverage including detailed reporting in The Atlantic on the resistance biology behind it.
Cheap international air travel is part of the story. Bedbugs are excellent hitchhikers, riding in luggage seams and clothing folds, and the volume of international travel increased dramatically between 1990 and 2015. But travel alone doesn’t explain why the bugs, once reintroduced, no longer collapsed under standard chemical treatment the way they had in 1955. The reason is inside the insect itself.
The mutations that survived DDT
DDT and the pyrethroid insecticides that replaced it after DDT was banned in the United States in 1972 work through the same basic mechanism: they jam open sodium channels in insect nerve cells, causing uncontrolled firing, paralysis, and death. Any mutation that changes the shape of those sodium channels — even slightly — can blunt the drug. In bedbugs, specific point mutations in the voltage-gated sodium channel gene do exactly that. Bugs carrying these mutations survive doses of pyrethroids that would have killed their ancestors many times over.
Those mutations didn’t appear in the 1990s. They were already circulating at low frequency in bedbug populations during the DDT era, and the few individuals that carried them were the ones most likely to survive spraying. Their descendants are what came back. Detailed genetic analysis of the bedbug genome has confirmed that modern infestation strains around the world share the same suite of resistance alleles, consistent with a bottleneck-and-rebound pattern rather than a fresh emergence.
The layered defenses go further than the sodium-channel change. Modern bedbugs also overproduce cytochrome P450 detoxifying enzymes that chemically break down pyrethroids before they reach the nerve, and they have thickened cuticles that slow chemical absorption through the exoskeleton. Research on resistance mechanisms in bedbug populations describes strains that tolerated pyrethroid doses several thousand times the lethal dose measured in a susceptible laboratory colony maintained since the 1970s.
Why this is textbook natural selection
Bedbugs reproduce quickly — a female can lay several hundred eggs in her lifetime, and generation time is measured in weeks at room temperature. In a heavily treated apartment building, a chemical spray becomes a filter: the 99% of bugs without resistance mutations die, and the 1% with them inherit an empty apartment full of sleeping hosts. Within a few generations the entire population is resistant.
The same process has been documented in cockroaches, houseflies, mosquitoes, and agricultural pests. Genomic monitoring of pesticide resistance has found the pattern is now routine enough that resistance alleles can be tracked in near real time as they spread through populations. In urban cockroaches, the same kinds of sodium-channel mutations and detoxification-enzyme upregulation appear again and again, in different cities on different continents, evolving in parallel wherever the same chemicals are used.
What makes bedbugs unusual is the completeness of the historical record. Because they were nearly eradicated and then came back, there is a clean before-and-after. The pre-DDT museum specimens sitting in entomology collections at institutions like the Smithsonian and the Natural History Museum in London can be sequenced and compared directly to modern infestation samples. The mutations that spread are visible in the genomes.
Paris, 2023, and the shape of the problem
The Paris episode of autumn 2023 became a public illustration of what resistance means on the ground. Videos of bedbugs on Métro seats circulated widely, France’s transport minister convened a meeting with operators, and the government announced an anti-bedbug plan ahead of the 2024 Olympics. Analyses by Beyond Pesticides and other groups tracking the Paris surge pointed directly at pyrethroid resistance as the reason ordinary sprays weren’t clearing infestations, and at the way over-the-counter treatments had been selecting for resistant strains in French housing for years.
Modern professional treatment now leans away from chemistry that the bugs have already defeated. Heat treatment — raising the temperature of an entire room to lethal levels for several hours — kills bedbugs at every life stage, including eggs, and there is no obvious evolutionary route around it. Insects cannot easily evolve resistance to physical denaturation of their own proteins. Steam, vacuuming, encasement of mattresses, and desiccant dusts like diatomaceous earth and silica gel work on similar physical principles. Chemical treatments are still used, often in rotation with neonicotinoids or insect growth regulators that attack different biological targets, but the era of a single spray solving the problem is over.
The bite that goes unfelt
A bedbug feeds for several minutes, injecting saliva that contains an anesthetic and an anticoagulant so the host doesn’t stir and the blood flows freely. Adults are about the size and shape of an apple seed, flat enough to slide into the gap between a mattress and a bed frame, and they can survive without a blood meal for months — in some laboratory conditions, more than a year. They find hosts largely by tracking exhaled carbon dioxide and body heat.
Reinfesting the developed world required only a handful of resistant founders arriving in luggage or secondhand furniture. Once inside a building with shared walls, they can spread through wall voids and electrical conduits from one apartment to the next. In New York and Paris the pattern of spread through multi-unit housing looks almost identical, generation after generation quietly filling in the map.
What the resurgence really shows
The bedbug comeback is often described as a failure of hygiene or a consequence of banning DDT, but neither framing fits the evidence. Bedbugs are indifferent to cleanliness — they need blood, warmth, and hiding places, all of which a spotless five-star hotel offers as generously as a shared dormitory. And DDT would not work today either. The same mutations that block pyrethroids also confer strong cross-resistance to DDT, because both compounds target the same sodium channel.
What the bedbugs demonstrate is a slower, more sobering point about chemical control of any organism that reproduces quickly and lives in close contact with humans. Selection pressure applied for long enough, in large enough populations, will find a way through. The bugs that came back in 1997 are, in a real biological sense, the great-great-great-grandchildren of the ones that survived the sprays of 1947. They have been quietly evolving inside our walls the whole time.
The itch that a New Yorker or a Parisian wakes to at three in the morning today is being delivered by an insect whose ancestors were, half a century ago, considered nearly extinct in that city. The bugs did not come back because we forgot how to kill them. They came back because a small number of them had already learned how not to die.
