When it comes to mealtime menus, spider don't limit themselves to chowing down on insects, researchers have found; some species are happy to feast on small types of freshwater fish their own size or even larger.
Scientists have for some time been aware some spiders will dine on fish, but a new study has revealed the phenomenon is more geographically widespread and more common than previously realized.
Fish-eating spider species inhabit every continent on the globe with the exception of Antarctica, the researchers report in the science journal PLOS ONE.
"Fish may represent a 'big-ticket item' in the nutritional budget of semi-aquatic spiders," zoologist and study leader Martin Nyffeler of the University of Basel in Switzerland says.
Fish as prey may be a particularly attractive food source during mating periods to satisfy the elevated protein needs of pregnant female spiders, he added.
Semi-aquatic species -- spiders that can swim and dive or even walk on the surface of water and inhabit the margins around shallow streams, ponds, lakes or swamps -- use powerful neurotoxins to kill fish.
Their choice of an aquatic diet means they've given up on spinning webs, preferring instead to utilize a hunting technique that involves holding on to a rock on plant at the water's edge with their hind legs while resting their front limbs on the water's surface.
Once they've snagged their prey, they will drag their catch to a dry rock or a tree trunk and inject potent enzymes to dissolve the fish's tissue and provide a meal, the researchers said.
"Fish meat is high-quality prey regarding protein content and caloric value," Nyffeler said. "It takes a spider usually many hours to devour a fish until nothing is left but bones and scales."
Researchers say they've observed at least 18 species catching fish in the wild, mostly in warmer climates.
Fish from one inch to as large as 2-1/2 inches long have been seen being caught by aquatic spiders, they said.
One species in Australia, Dolomedes facetus, has been known to steal goldfish from suburban garden ponds, they reported.
In addition to fish, some spider species are known to prey on vertebrates including frogs, mice, birds and bats.
"Spiders are more adept predators than most give credit for," study participant Brad Pusey of the University of Western Australia says.
Perhaps it's time to add another line to the old "Come into my parlor, said the spider to the fly," refrain. Maybe something along the lines of, "Hey, wanna go for a swim in my pool?"