Since they first terrified viewers in the 1979 classic Alien, xenomorphs seem to have only gotten harder to beat. In the soon-to-be-released Alien: Covenant, they are even better at rapidly colonizing their victims, using warm bodies as incubators before blasting offspring outward — not just via the traditional chestburster route but now also through the spine. The new film is a terrifying reminder that xenomorphs are practically unstoppable.
But don’t lose hope, parasitologist Mark Siddall, Ph.D. tells Inverse. They’re not totally invincible.
Siddall, a parasite expert and curator at the American Museum of Natural History, explained to Inverse that xenomorphs are a type of parasite known as a parasitoid — that is, only one part of its life cycle is considered parasitic, and the rest of it is spent free living. Understanding this is key to exploiting its two major flaws, he says.
The parasitic phase of the life cycle that Siddall is referring to is the facehugger-to-chestburster phase of the xenomorph life cycle: Xenomorph eggs can hang out for millennia without a host, but eventually they require a warm body to use as a host in order for the embryos to mature into their adult forms. The eggs are what make the species so hardy as a whole, but they also represent the species’ Achilles heel. Parasites, after all, can’t survive as a population if you take away their only means of reproducing.
“There’s one that we saw in the second movie and that’s a very clear sense of parental care,” said Siddall, referring to the alien’s flaws revealed in the 1989 sequel Aliens. “[If] you threaten the xenomorph’s eggs, then the xenomorph will back off.” In other words, if a xenomorph queen came to Earth and studded our cities with her eggs, we could halt the growth of the parasite population by exploiting her sentimentality and stopping the life cycle at its origin.
Of course, that’s easier said than done because the eggs are themselves pretty dangerous. “The xenomorph in the movies requires someone to stare inside of this egg that can’t move and be stupid enough to do it,” Siddall says. The ironic part is that this relatively passive infection strategy is actually the xenomorph’s second big flaw, he explains; while real-life parasites like wasps grab their victims and forcibly inject them with their eggs, the xenomorph has to wait for its hosts to come along. “So far it has been portrayed in the movies it’s fairly dependent on our stupidity,” Siddall says.
Not all hope is lost, however. Education and compassion, he explains, are key to beating any parasite, fictional or not. In real life, the transmission of human parasites like the guinea worm has been reduced to near zero because affected populations have been educated about how to avoid infection through the compassion of other humans. In the case of a xenomorph infestation resulting from people peering into eggs and accidentally getting infected, Siddall says, “we can actually get in front of its life cycle by educating people not to do that.”
While he doesn’t think it’s likely we could defeat xenomorphs outright — and, judging by their looks in the new movie, they feature some killer parasite characteristics we haven’t considered before — Siddall doesn’t think the prospect of a xenomorph takeover would be totally hopeless for us.
“I’d like to think we’re smarter,” he says. “And so far we’ve been able to survive a lot of parasites and a lot of pestilence because one, we’re smart, and two, we’re compassionate, and as long as we hold on to those two things I’m pretty sure our species will survive.”