May these mosquitoes live long and prosper. — Dan

We call “bugs” bugs because they bother us — they’re not something you typically want around. And among the most annoying of bugs are, perhaps, mosquitos. Mosquitos are a disease vector and spread a lot of the world’s most scary illnesses, including malaria, dengue, West Nile virus, and yellow fever, according to the World Mosquito Program (WMP). Efforts to stop the spread of these diseases often center on efforts to stop the spread of mosquitoes themselves.

But there may be another, better solution: make more mosquitos.

As Scott O’Neill, founder of the WMP, told the University of Chicago’s Big Brains Podcast, the problem with attacking mosquito populations is that we just can’t do it at scale — “they’re really hard to kill, and we really haven’t worked out good ways to kill them.” So O'Neill and his team at the World Mosquito Program tried something different. Instead of killing mosquitoes, they decided to breed them — millions upon millions of them.

The work started in a factory in Curitiba, a city in southern Brazil. It’s not like any other factory, though — there aren’t any self-sealing stem bolts being attached to random widgets by reverse-ratcheting routing planers or the like. Here, you have a lot of people in hazmat suits pouring loads of mosquito larvae into large vats of water. Once the mosquito eggs hatch and the grow, per NPR, they’re transferred to another room, where “mesh cages teem with mosquitoes that feast on small bags of blood.” Only after the bugs reach the appropriate stage of maturity are they collected and brought to the location needed, and then released into the wild.

These mosquitos, though, contain a secret weapon — a bacteria called Wolbachia that appears in about 60% of insects worldwide, according to the CDC. And also according to the CDC, mosquitoes with Wolbachia can’t make people sick — the bacteria essentially crowds out the pathogens, preventing them from replicating inside the mosquito's body. A mosquito that can't grow dengue virus can't spit it out when it bites you. So for us humans, at least, there’s little to no downside of having these mosquitoes flying around.

But for the bad mosquitoes that want to reproduce? That’s where the real value of these special bugs come into play. Wolbachia-carrying mosquitoes can be used to, effectively, inoculate wild populations against the disease they spread. When factory-raised males mate with wild females, either the eggs don't hatch (reducing the population) or the offspring carry Wolbachia too (reducing disease transmission). Either way, the humans win.

The factory in Curitiba is just one of many now open throughout the world. The program has already been deployed in Brazil, Colombia, Indonesia, Australia, and Mexico — and it's working. Communities in Texas and California that have released Wolbachia-carrying mosquitoes report significant drops in the regular mosquito populations, and the CDC notes that Singapore, Thailand, and Puerto Rico have tested the approach as well. The mosquitoes aren't genetically modified, the bacteria dies when the insect dies, and the EPA has determined that releasing them poses no environmental risk.

There's a catch, though. Once you stop releasing the factory-bred mosquitoes, the wild population slowly returns to normal levels. Lab-raised mosquitoes are not a one-time fix but an ongoing intervention — which is why having a factory that can churn out millions of disease-fighting bugs matters. O'Neill's goal is ambitious: he wants his nonprofit to eventually go out of business because the problem is solved. Until then, the mosquito factories will keep humming, mass-producing one of humanity’s strangest public-health tools: more mosquitoes.

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Today’s Bonus fact: In 1900, an American doctor named Jesse William Lazear wanted to prove that mosquitoes spread yellow fever, so he purposefully let an infected mosquito bite him. He turned out to be right — he came down with the illness shortly thereafter. But it was among one of the last things he did. Lazear died from yellow fever just seventeen days after the mosquito bite.

From the Archives: It Doesn't Stand for “Eradicating Dangerous Mosquitoes”: but maybe it should?

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And thanks! — Dan