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New Spider Species Discovered In Indiana Cave

The translucent sheet-weaving spider shows that scientists haven’t yet found everything in our own backyard

Islandiana lewisi, found in a single cave in southern Indiana (Dr. Marc Milne)
smithsonian.com

You might expect to hear about a new species discovered in, say, a remote jungle or a far-flung desert. But especially when it comes to stuff like microbes, fungi and insects, the find might be much closer to home. Case in point: Islandiana lewisi, a translucent sheet-weaving spider recently discovered in a single cave in Indiana.

Sherry Noik at the CBC reports that the tiny, 2-millimeter-long arachnid was collected by University of Indianapolis arachnologist Marc Milne in southern Indiana’s Stygeon River Cave back in October 2016. Julian Lewis, a cave researcher and president of the Indiana Karst Conservancy, first found the tiny critters while spelunking in the flood-prone cave system, and had tipped Milne off about the translucent spiders. When the arachnologist visited the cave system himself, he found horizontal webs strung between muddy boulders and a bunch of little spiders in the main chamber of the cave. “I didn't know what the spider was at first,” Milne says in a press release. “I just thought it was odd that so many were living within this dark cave with no other spider species around.”

Spiders, especially little ones, are a challenge to identify, so he brought the specimens back to the lab for a closer look. “Usually the way to tell spiders apart is to look at the genitalia and see which ones can breed with which ones,” he tells Noik.

But the genitals didn’t immediately reveal the whole story. According to the release, during his first examination, Milne believed that the spider was a previously discovered Islandiana cavealis, which is found in Kentucky. But a few months later, when he looked again, he spotted some differences. For instance, the cavealis’s eyes have almost disappeared, while lewesi has well-defined eyes, which means they probably haven’t been living in caves quite as long. Other morphological differences also indicated that what he was examining was a new species. The spider is described in the journal Subterranean Biology.

Lewisi, named after Lewis, is the 15th species discovered in the genus Islandiana and only the fifth cave dweller among them. The last new species added to genus was Islandiana cristata, which was discovered back in 1987.

So what’s a nice little spider like lewisi doing in a muddy Midwestern cave prone to flooding? Milne tells Jessica Boddy at Gizmodo that it’s likely a good hunting ground for a sheet weaver, which catches other small arthropods in its dense horizontal net-like webs. “Springtails are like little lunch sacks for spiders. They’re soft and packed with nutrients. When the springtails hop into the air, they can land and get stuck in these sheet webs,” he says, though this interaction hasn’t been observed with the new spider yet.

The find also highlights the fact that biologists still don’t know everything that’s out there, not by a longshot. “[E]ven in our backyard, there are a lot of new, undiscovered organisms that we don’t know much about,” Milne tells Body.

It’s not all tiny, translucent arachnid finds, either. Last year, researchers announced the discovery of a new spider species in a Mexican cave that is the width of a softball. Earlier this year in January, researchers described in detail 18 new species of spider-hunting pelican spiders discovered in Madagascar. Also in January, users of a new phone app discovered seven new species of spiders in Australia. There may even be one dangling over your head...right...now.

About Jason Daley

Jason Daley is a Madison, Wisconsin-based writer specializing in natural history, science, travel, and the environment. His work has appeared in Discover, Popular Science, Outside, Men’s Journal, and other magazines.

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