Researchers have found that nearly one fifth of all spider families are associated with saltwater or freshwater aquatic habitats. Their findings address the common misconception that all spiders dwell on land, and reveal surprising evolutionary pathways of this group from a land-based existence back to a water-based existence.

«This study shines a light on what was previously a dark corner of the spider tree of life,» says senior author Lauren Esposito, PhD, the Academy’s Curator of Arachnology. «It’s the most extensive literature review of aquatic spiders to date — we were blown away by the extent that spiders have evolved to interact with aquatic habitat.»

Illuminating «The Life Aquatic with Spiders»

To catalogue these water-dwelling spiders, the team first consulted years of prior research led by Academy colleagues. A spider group known as Dictynidae caught their attention: Although known to contain remarkable diversity of aquatic spiders from around the globe, the group presented tangled species relationships. Using DNA analysis, the team carefully studied and sorted specimens, flagging instances where a species evolved a full or partial association with water. Of 120 spider families across the tree of life, they found that members of 21 families exhibited an affinity for aquatic habitat. This group represents nearly one fifth of all spider families known to science.

«We’re grateful for the collaborative spirit of our colleagues, whose prior research laid the groundwork for our team,» says lead author Sarah Crews, PhD and an Academy researcher. «Not only were we fascinated by the Dictynidae group’s unique ecology and remarkable diversity, we also realized no one has ever given them a closer look.»

While some aquatic spider species share a common ancestor, the co-authors concluded that most are distant cousins with superficially similar traits — a phenomenon known as convergent evolution. Knowing the group lacked a single evolutionary origin, the study team set out to compile an «atlas of characteristics» to see if certain traits give spiders a leg up (or eight) when thriving in harsh, watery worlds.

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