Ed Yong begins by showing us beautiful images of animals gathering in large groups. And the reasons for them are fascinating and many. But Yong, an award-winning science writer, points out that most explanations “make an assumption about animal behavior — that they are in charge of their actions.”
But many animals gather in groups, in fact, because they are infected by parasites.
For example, the brine shrimp artemia salina — or sea monkeys — are often found in large red swarms that span for meters. Do they do it for safety or mating? No, they do it because they’re infected by tapeworms. The parasite changes their color, makes them live longer, and makes them congregate in groups. Those large, visible swarms make them easy prey for the flamingo, the final host for the tapeworm. “That is the secret of the artemia swarm,” says Yong. “It’s…
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