Science Shocker: Fleas Are Cousins of Flies

Specifically, scorpionflies. This last great mystery in the evolutionary tree finally resolved by grad student’s groundbreaking big-data genetics study

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Cats, dogs and furry mammals are a flea's favorite abode.
Cats, dogs and furry mammals are a flea's favorite abode. Credit: DreamBig / Shutterstock
Ruth Schuster
Ruth Schuster

Among the great mysteries bedeviling science are dark matter (what is it?), death (do we have to?) and what fleas are. Meaning, where do they belong on the tree of life? Now that last conundrum has been put to bed by University of Bristol undergrad Erik Tihelka. They are scorpionflies, a distant cousin of the fly.

Specifically, the closest living relatives of fleas are the scorpionfly family Nannochoristidae, “a rare group with only seven species native to the southern hemisphere,” the team wrote – New Zealand, southeast Australia, Tasmania and Chile. They aren’t flies exactly, but they are distant cousins of the actual fly. Scorpionflies are ethereal nectar-sipping beauties with rear ends that look remarkably like those of scorpions.

Although insects and scorpions both belong to the great family of arthropods, scorpions are actually arachnids and the similarity in the tush is a case of convergent evolution.

Asked why exactly the place of fleas on the evolutionary tree had been so perplexing, Tihelka explains. “They are very unlike all other insects. They have very curious mouthparts used to feed on blood, they jump, and their bodies are flattened from left to right. These are anatomical differences that separate from all other insects,” he tells Haaretz.

The common scorpionfly.Credit: Richard Bartz, Wikimedia Commons

A lot of insects feed on blood and a lot of others jump, but not like our friend the flea, he elaborates. Also, fleas split off from their buggy brethren a very long time ago, possibly before dinosaurs even evolved.

“We think [they split off] somewhere between the Permian and the Jurassic,” Tihelka says, adding that the oldest fossil fleas found so far date from the Jurassic. Which means the flea family may go back as much as 300 million years, from which point they followed their own bloody avenue, while scorpionflies continued to feed on flowers.

Moreover, after splitting off so long ago, fleas then evolved very fast, Tihelka says.

Why had the evolution of fleas and family been a mystery anyway, inquiring minds want to know.

A scorpion.Credit: Vijayakumarblathur, , Wikimedia Commons

Elucidating relationships on the tree of life can rely on various methodologies, one being genetic comparison. The more protein-coding genes two species have in common and the lesser the differences between them, the closer they are. Humans have more genes in common with the chimp than the nematode or tomato.

Fleas, however, split off so long ago and evolved so fast, building up mutations in their genome, that it was hard to pin down their closest relatives, Tihelka explains. Previous genetic research had suggested that fleas were related to scorpionflies, but that was based on relatively few genes, he adds.

His study is based on over 1,400 genes coding for proteins – not that the kids analyzed the genetics of fleas themselves. They applied cutting-edge algorithms to test all proposed hypotheses about the placement of fleas on the tree of entomological life, and searched for their closest kin.

This is the first time a big dataset has been used to achieve a more complex analysis of the evolution of the flea, he says.

A scorpionfly. Note its scorpion-like rearCredit: Charles J Sharp, , Wikimedia Commons

Like most of their entomological brethren, scorpionflies appreciate warm climes, but some of the roughly 600 species of scorpionfly actually thrive in the snow. And now thanks to Tihelka and colleagues, we know that fleas belong to the great greater family of scorpionflies. Fleas, by the way, prefer your dog or cat or any convenient hairy mammal whatever clime it’s in. They will dine on you if they have nothing better.

Asked why he decided to research this of all things, Tihelka says that the family relations of the flea was one of the last big mysteries in evolution.

“We [science] have been researching insects for 200 years, so the big questions of relationships have been resolved. This was last enigma,” he explains.

After all that evolution, today we have about 2,000 variants of flea, who do not have wings and who feed mainly on the blood of mammals and birds with the help of their unusual mouthpart – though it seems the flea and scorpionfly may have both evolved far before flowers did. So go figure what plant secretion they ate.

A cat trying to dislodge one of its flea residents.Credit: Vannie

“It seems that the elongate mouthparts that are specialized for nectar feeding from flowers can become co-opted during the course of evolution to enable sucking blood,” says Mattia Giacomelli, another doctoral candidate at the University of Bristol who participated in the study.

“The new results suggest that we may need to revise our entomology textbooks. Fleas no longer deserve the status of a separate insect order, but should actually be classified within the scorpionflies,” rules Chenyang Cai, associate professor at the Nanjing Institute of Geology and Palaeontology and a research fellow at the University of Bristol, specializing in Mesozoic insects.

By the way, the Jurassic fleas measured as much as 2 centimeters (about three-quarters of an inch) long. Even with the fleas’ role in disseminating the Black Plague in mind, we should count our blessings.

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