There's something fascinating about hairy little spider feet. They look like they belong on dogs. Or maybe even cats.
Recently, images of hairy spider "paws" have circulated on social media with people oohing and aahing about how cute they are and how much they resemble furry pet appendages.
Photographer Michael Pankratz's macro shot of a spider's furry foot — actually Avicularia geroldi, a species of tarantula — is making the online rounds, being likened to a dog or cat paw.
Photographer Michael Pankratz's photo of 'Avicularia geroldi adult male, pinktoe.' (Photo: Used with permission by Michael Pankratz/flickr)
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 MNN "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.
In one study researchers glued tiny transmitters to the backs of 30 whip spiders nabbed from the Costa Rican rainforest. In one group, they painted over their eyes with nail polish; in another they either painted over or trimmed the tips of their antenna-like front legs. They then took each spider about 11 yards from its home and released it. Most of the control spiders and the ones that were blinded by nail polish made it back home. However, the ones that lost the tips of their legs lost the ability to navigate.
The researchers think the spiders used smell sensors on their legs to find their way home but likely weren't sure exactly what smells they were following. "Therein lies the mystery," lead researcher Verner Bingman tells Discover.
Watch the whip spider experiment in this video: