Who Knew? Biologist Discovers Daddy Longlegs Has Four Extra Eyes

Because the spider called daddy longlegs has a particularly salient trait – namely its long legs – biologists never really considered the creature’s eyes, which were assumed to be a standard-issue pair situated at the top of the head. Now researchers have discovered two more sets of peepers, vestigial and useless, on the side.

“I couldn’t believe my eyes,” says Guilherme Gainett, lead author on the study that appears in the journal Current Biology. “It was one of those little moments that happens in science when you see something that no one has ever seen and get really excited.”

What Gainett couldn’t believe was the existence of visual proteins, or opsins, that are present on big-daddy embryos, revealed at the microscopic level. The researchers say these are vestigial eyes, structural remnants from an early point in the species’ evolution.

Vestigial organs aren’t totally useless because they link the ancient and contemporary traits of a species, allowing science to track an organism’s evolutionary path. The new discovery is particularly exciting because it jibes with a 400-million-year old fossilized specimen of the arachnid, which also had an additional set of lateral eyes on the side of the head. (The top citation in Gainett’s study is none other than Darwin’s “Origin of Species,” 1859.)

Daddy longlegs (Iporangaia pustulosa), also called harvestmen, are arachnids, but not spiders. Apparently there is still plenty to learn from them.

Photo credit: Thomas Bresson /  Wikimedia Commons