In the latest episode of the 80,000 Hours podcast, Kevin Esvelt talks about the New World screwworm. He claims that there is a potential for a massive animal welfare win, if we can eliminate this parasite. 

This feels worthy of a discussion, so I'm starting this thread. Is this issue on anyone's radar? Has anyone looked into these claims? They seem potentially important/actionable, if true! 

Relevant section from the podcast:

Kevin Esvelt: [...] the New World screwworm, which has the amazing scientific name of Cochliomyia hominivorax: “the man devourer.” But it doesn’t primarily eat humans; it feeds indiscriminately on warm-blooded things, so mammals and birds. It’s a botfly that lays its eggs in open wounds, anything as small as a tick bite. And it’s called the screwworm because the larvae are screw-shaped and they drill their way into living flesh, devouring it. And as they do, they cultivate bacteria that attract new gravid females that lay more eggs and continue the cycle.

So you have this macabre dance of parasitisation that results in the animal being devoured alive by flesh-eating maggots. And we know that it’s horrendously painful, because people get affected by this, and the standard of treatment is you give them morphine immediately so that surgeons can cut the things out — because it’s just that painful; it’s unbelievably agonising. And by my back-of-the-envelope calculations, there’s about a billion hosts of this every year — so a billion animals are devoured alive by flesh-eating maggots every single year.

We even know that we can eradicate this species from at least many ecosystems and not see any effects, because it used to be present in North America too, and we wiped it out using nuclear technology, oddly enough. Some clever folks noticed if you irradiate the larvae, then they grow up sterile. And if you release enough of them, then the wild ones will mate with a sterile one, and they only mate once, so you can suppress the population to the point of not being there anymore.

So we did this first up through Florida and then across the West, and then down through Texas to the Mexican border. The US Department of Agriculture then inked a deal with the Mexican government to eradicate them from Mexico because the southern border was shorter and therefore cheaper. And then they just went country by country down Central America to Panama. The southern border of Panama is the shortest, so American taxpayer dollars today contribute to the creation and maintenance of a living wall of sterile screwworm flies released in southern Panama that prevents the South American screwworm from reinvading North America — 10 million released every week.

Luisa Rodriguez: Wow.

Kevin Esvelt: But there’s too many of them in South America to wipe out by that means. And so the way forward is obviously gene drive. If the Mercosur countries agree that they want to get rid of the New World screwworm, they can start with something like a daisy drive locally — and Uruguay is working on this — then they can wipe it out from their country. Uruguay loses about 0.1% of their total country’s GDP to the screwworm because they’re so dependent on animal exports. I mean, Uruguay and beef is… To those listeners who eat beef, I’m going to start fights here, but it’s better than beef from Argentina, even. But anyway, they’re all very concerned about their beef, and screwworm is horrific.

It also, of course, preferentially hurts poor farmers who struggle to afford the veterinary treatments for their animals. And of course, they hate to see it, because here you’re watching these animals that you’re caring for literally get devoured by flesh-eating maggots, and it’s agonisingly painful.

But from an animal wellbeing perspective, in addition to the human development, the typical lifetime of an insect species is several million years. So 10⁶ years times 10⁹ hosts per year means an expected 10¹⁵ mammals and birds devoured alive by flesh-eating maggots. For comparison, if we continue factory farming for another 100 years, that would be 10¹³ broiler hens and pigs. So unless it’s 100 times worse to be a factory-farmed broiler hen than it is to be devoured alive by flesh-eating maggots, then when you integrate over the future, it is more important for animal wellbeing that we eradicate the New World screwworm from the wild than it is that we end factory farming tomorrow.

The ethics of CRISPR [02:38:34]

Luisa Rodriguez: What a take. I also love the application of gene drives for animal suffering in particular. I’d heard of many applications for human benefit, but the idea that we could make a dent on some wild animal suffering was just really moving to me. I feel like there are loads of concerns about kind of messing with an ecosystem. In this case, it’s already happening, just through a different method that can’t be scaled up — so it just seems like a really great case of how we’ve got this way to scale it up much bigger, eradicate this horrible insect in more places.

Kevin Esvelt: It might matter to some listeners, they might be concerned about the moral implications of actually driving a species to extinction. Which, of course, is also what we’re proposing for the malaria parasite (but not the mosquitoes) and also for the schistosoma. But for something that is not a major human disease, that’s [not] a microbe, here we’d be proposing eradicating the screwworm itself — the fly, the macroscopic thing from the ecosystem everywhere in the world.

But it’s worth noting that this is actually reversible, because screwworm is one of those comparatively few insects whereby you can freeze the larvae and unfreeze them decades later and they’re perfectly viable. So we don’t have to drive them extinct, we just need to remove them from the wild and then we can keep them on ice. So if for some reason we decide we need them again later, we can reintroduce them. It’s just we’ve got to ensure, if you want the animal welfare benefit…

One of the things that really I find attractive is, when you think about how much suffering humans have inflicted on animals in the course of our species, it almost certainly does not outweigh 10¹⁵ mammals and birds devoured alive by flesh-eating maggots. So to the extent that we’re now net negative on the scale, all we have to do is, before civilisation collapses, or we disassemble the Earth or whatever futurists think we’re going to be doing — or even if we lose, even if we fail and civilisation collapses, or even we go extinct — as long as we remove the New World screwworm first, we will be in morally net positive territory when it comes to our impacts on other species’ wellbeing. That’s tremendously inspiring.

Luisa Rodriguez: Yeah, I completely agree.

Kevin Esvelt: But it’s none of my business, because I don’t live in South America. It’s their environment; it’s their call. And so I would urge folks, if you want to reach out and know who to support in South America to fund that project, I’d be happy to connect folks — but moralising about how they have this moral duty to do this for the benefit of all humanity, probably not very helpful. If they decide to do it, it’s going to be for their own reasons, and us hectoring them is not going to be useful to the cause if you care about seeing it happen.

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