An electric eel donated to a natural history museum in 1873 had two ticks embedded in its skin, making it the first known instance of ticks parasitizing a fish. But it was never documented until now, more than 150 years later, when a curator and tick specialist chanced upon the specimen, identified the ticks, and reported the case in the Journal of Medical Entomology. Shown here are the Amblyomma cajennense ticks embedded on the Electrophorus varii electric eel, housed in the collections of the Museum of Comparative Zoology at Harvard University. (Image originally published in Chong 2025, Journal of Medical Entomology)

By Melissa Mayer

Melissa Mayer

Ever since she was a kid, Kaylin Chong has loved museums.

That’s how she wound up in Harvard’s Organismic and Evolutionary Biology doctoral program, where she also works at the Museum of Comparative Zoology. She hunts for ticks in the museum’s collections as a side project.

There, a chance encounter led her to a wild discovery: two ticks feeding on an electric eel. Chong reported the find in an article published in October in the Journal of Medical Entomology. It’s the first known instance of ticks parasitizing a fish—ever.

“It was honestly by accident,” she says. “I was looking at a bunch of iguanas from the Dominican Republic that had tons of ticks, and one of the iguanas was still sitting on the desk. The ichthyology curatorial associate, Andrew Williston, came in and was like, ‘Someone working on ticks? There’s a tick in our collection.'”

An electric eel donated to the Museum of Comparative Zoology at Harvard University in 1873 had two ticks embedded in its skin, making it the first known instance of ticks parasitizing a fish. But it was never documented until now, more than 150 years later, when Kaylin Chong, a doctoral student at the museum, chanced upon the specimen, identified the ticks, and reported the case in the Journal of Medical Entomology. (Photo courtesy of Kaylin Chong)

At first, Chong thought they must be mistaken. While some ticks can remain underwater for 70 days—and possibly longer as nymphs—there’s been no record of them feeding on fish of any kind. But subsequent inspection confirmed the unbelievable: The electric eel specimen had two Amblyomma ticks embedded in its side.

The eel was collected—more than 150 years ago—by Charles Linden, a high school teacher and bird specialist. Back in 1872, he embarked on a collecting expedition to Brazil and returned with 210 skins, representing 100 species. In 2009, someone at the museum noted the ticks on the eel’s digital record—but you’d have to specifically search for ticks within the fish database to find it.

Now those ticks were firmly in Chong’s sights.

“I truly lost so much sleep,” she says. “I was like, ‘Oh my god, I have to pull a tick out of the eel. What if the mouth parts get stuck inside? What if I mess this up? I only have two ticks, and I have to pull out one and keep the other one there, so people believe me.”

Fortunately, the tick came out with no problems, sliding from the eel’s smooth, scaleless skin with a satisfying pop.

From there, Chong imaged the specimens and worked with taxonomists to confirm her identifications. The eel, once classified as Electrophorus electricus, now belongs to Electrophorus varii after scientists split the species into three. The ticks are Amblyomma cajennense, an Amazonian species that feeds mostly on mammals, especially those with hooves. Until now, there weren’t records of these ticks feeding on any cold-blooded vertebrates.

So, how did these parasites come to feed on this unlikely host? That remains a mystery.

It’s possible that Linden pulled the freshwater eel from the water and left it to weaken on the bank. The ticks could have chanced upon the eel and began feeding. Eventually, they were preserved along with it.

But it’s also possible the ticks encountered the eel earlier as it crossed the land, moving between two bodies of water, as these eels are known to do. Other kinds of Amblyomma ticks have been documented feeding on sunbathing sea snakes and even a saltwater crocodile, both reptiles that go back and forth between land and water. The ticks boast a pair of water-repelling plates on their bellies that trap a pocket of air, allowing submerged ticks to breathe underwater like tiny, bloodthirsty scuba divers.

Whether the ticks can feed underwater is still unknown.

For Chong, this find and the remaining mystery highlight the value of natural history collections—not just for sampling DNA from relict specimens but also for traditional observational work that challenges what we know about the world around us.

It’s a stark reminder that our museums aren’t expendable—and a call for ichthyologists and other specialists to take a closer look at their preserved specimens. Maybe there are other unlikely ticks out there.

“And then call me,” Chong laughs. “I’ll happily pull them off.”

Melissa Mayer is a science writer and the human behind Washington State University’s science cat, Dr. Universe. Email: [email protected].