Some young fruit flies’ eyeballs literally pop out of their heads

In an hour of awkward puberty, eyes on these males rise out on skinny stalks

A male fruit fly with a long skinny red body and long dark eyestalks with red tips, stands on a leaf

A long skinny male fruit fly (Pelmatops tangliangi) prowls shrubbery with eyeballs sticking out at the end of stalks on its head. This fly’s swift and weird extension of its eyes has just been documented.

Yong Wang

Body changes at the brink of adulthood can get awkward in humans. But at least our eyes don’t pop out of our heads on stalks longer than our legs. Such high-rise eyes, however, give macho pizzazz to the adult males of some fruit flies.

Pelmatops tangliangi is one of the stalkier species of these flies. It morphs to its grown-up, eyes-out state in just 50 minutes, a new study reports. Once stretched, the skinny eyestalks darken and harden. That keeps the eyes stuck out like selfie sticks for the rest of these guys’ lives.

A collage of images capturing a male fruit fly's eyes extending. The first image shows the eyes only slightly bugging out of the head. Subsequent images show the stalks growing longer, first curly and then long and straight
Images from a lab video show the somewhat awkward stages of eye extension in a male fruit fly (Pelmatops tangliangi). This fly guy emerged from a little capsule where he changed from a plump wormy larva into a sleek adult. Just 16 minutes after exiting the capsule, the eyes are still close to his head (A). Over the following 34 minutes (B–H), the gangly eyestalks grow and eventually darken, stretching the eyes away from the body. The following day, the fully periscoped adult is ready to explore.N. Huangfu et al/Annals of the Entomological Society of America 2022

Biologists have known that eyestalks evolved in eight different fly families. Yet Pelmatops flies have gotten so little scientific attention that a lot of their basic biology has been a string of question marks. Now scientists have gotten a better picture of P. tangliangi’s eye lift. The first published photo sequence of their eyestalks stretching appeared in the September Annals of the Entomological Society of America.

Video images show that the eyestalks curl and rise irregularly. Yet “they are not flopping around while partly inflated,” says insect biologist Xiaolin Chen. This evolutionary biologist works at the Chinese Academy of Sciences in Beijing. Those eyestalks, she says, “seem slightly stiff, but still flexible.”

Females of the species may raise eyestalks too — if Chen’s team has found the right females. Chen suspects that what are now named as two species may be just two sexes of the same species.

Researchers don’t know much about these flies because there have been so few to study. The new paper describes a male P. tangliangi mating with a female known by a different species name. Her shorter stalks weren’t as magnificent as his.

While the headgear can burden a flying insect, long eyestalks may give flies some swagger. These Pelmatops and other kinds of stalk-eyed flies sometimes face off. They can go eyestalk to eyestalk with uppity intruders. But there’s no knocking and locking stalks in fierce fly disputes. Any pushing and shoving, Chen says, is “done with other body parts.”

Extreme eyes also may have other benefits. In the wild, Chen finds these fruit flies on long stems of some berry brambles. The eyes naturally periscope outward and upward. That allows the flies to spot danger while the body stays hidden in the greenery.

Susan Milius is the life sciences writer at Science News, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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