New Species of ‘Bizarre’ Giant-Eyed Insect Discovered in Washington Fossil

Big-headed fly

A “bizarre” fossilized bug whose head was nearly covered by two giant, bulbous eyes may help explain the evolution of unusual predatory insects that are still flying today, paleontologists say.

The 50 million-year-old fossil, found by a student on a field trip to a quarry in Republic, Washington, contains a nearly intact insect belonging to the family Pipunculidae, whose members today are known as “big-headed flies.”

Big-headed fly
A modern big-headed fly shows its head covered by compound eyes. (Photo: Nikola Rahmé)

While noted most for their eyes that seem almost unfeasibly large, the flies are also prized by farmers and other growers who cultivate them for the attacks they wage on leaf-eating bugs, which the big-headed flies use as hosts for their young.

Big-heads implant unsuspecting insects like leafhoppers with their larvae, who then eat their hosts alive from the inside until the baby flies hatch.

Though gruesome, this behavior isn’t particularly unusual in nature. And the new fossil — along with two similar ones uncovered nearby in British Columbia — may reveal how the Ancient West’s rapidly changing environment might have helped make it possible, according to Bruce Archibald, a biologist at B.C.’s Simon Fraser University.

“Big-headed flies are a group of bizarre insects whose round heads are almost entirely covered by their bulging compound eyes, which they use to hunt for mainly leafhoppers and planthoppers, renowned common garden insect pests,” Archibald said in a statement.

“The newly discovered species were preserved in Eocene epoch fossil beds that are 49 million to 52 million years old, which is about 12 million to 15 million years after the extinction of the dinosaurs.

“This great extinction event also disrupted forests in which the dinosaurs had lived, with mostly low diversity and greatly disrupted food webs for millions of years.”

However, the newly found fly lived just as these forests were recovering their lush diversity, Archibald noted, when new kinds of life were first starting to appear, including flowering trees like birches and maples.

Big-headed fly fossil
The new species of fossil big-headed fly was named Metanephrocerus belgardeae, after its discoverer, Azure Rain Belgarde of Collville, Wash. (SFU)

And with the arrival of flowers came whole new breeds of insects — namely pollinators and other specialized plant-eaters — that would be ready prey for a novel type of predator like the big-headed fly.

“With these new discoveries, we see that the early history of these oddly shaped insect predators provides a part of the puzzle revealing the broad ecological-evolutionary revolution of expanding predator-prey relationships and increasing biodiversity during the formation of new ecosystems,” Archibald said.

The Washington specimen’s unique features earned it the designation as a new, if now extinct, species, Metanephrocerus belgardeae, named after the student, Azure Rain Belgard, who found it. [See a fossil dinosaur recently discovered by a high-school student in Utah.]

Archibald and his colleagues report their finds in the journal The Canadian Entomologist.

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S. Bruce Archibald, Christian Kehlmaiera, & Rolf W. Mathewes (2014). Early Eocene big headed flies (Diptera: Pipunculidae) from the Okanagan Highlands, western North America The Canadian Entomologist DOI: 10.4039/tce.2013.79

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