The Odd, Adorable Mystery of Hairy Spider Feet

There's something fascinating about hairy little spider feet. They look like they belong to dogs. Or maybe even cats. Or some curious creature that sprang from the brain of Dr. Seuss.

From time to time, images of hairy spider "paws" make the rounds on social media with people oohing and aahing about how cute they are and how much they resemble furry pet appendages.

But those fuzzy feet — technically spider claw tufts — have all sorts of interesting purposes.

Arachnologist Norman Platnick, curator emeritus at the American Museum of Natural History, tells Treehugger, "the similarity to dogs or cats is only in the mind of the beholder."

All spiders have some hair-like structures, called setae, on their legs. But not all have claw tufts, which are hairy areas surrounding claws at the end of their legs.

"About half of the spider families have claw tufts. These animals usually have only two claws at the tips of their legs, and are usually hunting spiders, who pursue their prey," Platnick says. "Web-building spiders typically have three claws; the two paired claws, like those found in hunting spiders, plus a third, smaller, unpaired claw that helps them maneuver on their silk threads."

Cats and dogs don't have to use their feet for as many tasks as spiders do. Here are a couple of cool examples:

Spiders Use Their Feet to Stick

"The claw tufts of these spiders provide additional adhesive properties, making it easier for the animals to climb," Platnick says. "For example, many tarantulas can even climb up glass, despite their relatively heavy weight."

Because the tiny hairs on their feet are both small and flexible, they are able to make contact with many parts of a surface, clinging more easily, even when upside-down. Their attachment is dynamic, meaning it's only temporary. Because of this malleability, National Geographic likens the adhesion to being like that of a Post-it note, versus a barnacle's super glue.

“Permanent attachment systems, like glue, are often much stronger and not reusable, whereas temporary attachment systems, like hairy adhesive pads, can be used multiple times [and] adhere strongly enough to hold the animal, but the contact can be loosened very quickly and effortlessly,” Jonas Wolff, a biologist at the University of Kiel in Germany, told NatGeo.

Spiders Use Their Hairs to "Hear" and "Smell"

Many spiders have modified setae on the last segment of their legs that they use for sensory purposes, Platnick says. "For example, many spiders have trichobothria [vertical hairs] that are extremely sensitive to both airborne and substrate vibrations (i.e., they 'hear' with their feet). Many spiders also have modified setae that are chemosensory (i.e., they also 'smell' with their feet)."

According to the Australian Museum, these hairs are so highly sensitive to airborne vibrations that the spider can sense the wing beats of a moth or fly as it approaches or be alerted to the presence of a predatory wasp. One study found that spiders can hear and respond to sounds more than 3 meters (10 feet) away!

While the paws of puppies may be near and dear to our hearts, may we never forget to swoon over the claw tufts of our arachnid friends as well.