The Galápagos Islands are famous for inspiring Charles Darwin’s theory of natural selection — their unique plants and animals have been studied for over a century. But while giant tortoises and finches steal the spotlight, there’s a whole hidden world on these islands that rarely makes the headlines: parasites.

Our recent research shines a light on one of the least reported groups — parasites living inside the islands’ mammals. Specifically, we focused on the nematodes (roundworms) and tapeworms of Galápagos rodents. What we found was remarkable: a brand-new species of tapeworm living inside one of the rarest rodents on Earth — the Santiago rice rat (Nesoryzomys swarthi).

The story of this rat is extraordinary in itself. It was once thought to be extinct, until a 1999 expedition led by mammalogist Robert C. Dowler from Angelo State University rediscovered it alive and well on Santiago Island. That same expedition collected samples of the rodents’ parasites — providing the first evidence that the rice rats’ hidden hitchhikers were also thriving.

The Galápagos Islands are volcanic and lie about 900 km west of Ecuador, separated from the mainland by deep ocean. Any land-based species here must have arrived by long-distance journeys, most likely “rafting” across the sea on mats of vegetation washed out from flooded South American rivers. That’s impressive enough for a small rodent — but even more intriguing is that their tapeworm parasites appear to have made the journey too.

Somehow, these stowaway parasites survived the voyage and adapted to their new home. On the islands, they found an intermediate host — a local species that plays a crucial role in their life cycle — allowing them to continue thriving for generations.

We named this new species Raillietina dowleri in honour of Robert Dowler, whose work was key to rediscovering the Santiago rice rat and, in turn, uncovering this fascinating parasite.

The discovery isn’t just about a single species of tapeworm. It’s a reminder that even in one of the most studied natural laboratories in the world, there are still hidden connections and ancient journeys waiting to be uncovered — sometimes in the smallest, least expected places.

Read the full study in Parasitology: Helminth parasites of Galápagos mammals – a new cestode of the genus Raillietina from the endemic rice rat Nesoryzomys swarthi and a summary of parasites from both endemic and invasive rodents