According to a study published 15th July 2021 in the open-access journal PLOS Biology by Massimo De Agr of Harvard University in the United States, jumping spiders can distinguish living from non-living objects in their peripheral vision using the same cues used by humans and other vertebrate animals.
Any animal’s ability to sense other living species in their environment is critical for finding mates, evading predators, and catching prey. Because their inflexible, jointed bones and exoskeletons constrain the relative positioning of specific bodily parts, vertebrates and invertebrates’ motions differ from inanimate things.
From very limited visual information, such as a point-light display that shows dots representing the positions of the primary joints, most vertebrates can recognize this biological pattern of movement.
Spiders are arachnids, a class of arthropods that also includes scorpions, mites, and ticks. There are more than 45,000 known species of spiders, found in habitats all over the world. There’s a spider with a cartoonish butt, spiders that can jump on demand, and cannibal spiders that look like pelicans.
Researchers employed a spherical treadmill to partially constrain 60 wild-caught jumping spiders (Menemerus semilimbatus) and used a computer screen to produce point-light displays on each side of their peripheral vision for the first time to explore this phenomenon in invertebrates (only visible to their lateral eyes).
In this experiment, we observed how they alone can tell apart living from non-living organisms, using the semi-rigid pattern of motion that characterize the formers and without the aid of any shape cue. Finding the presence of this skill, previously known only in vertebrates, opens up new and exciting perspectives on the evolution of visual perception. My co-authors and I can’t wait to see what other visual cues can be perceived and understood by these tiny creatures.
They discovered that spiders who moved in a more biological fashion, with the spacing between joints restricted, were more inclined to want to turn and face displays that exhibited random movements.
The findings appear to contradict spiders’ expectations that they should concentrate their attention on objects in their environment that appear to be living possible prey, partner, or predator.
The word “spider” brings up visions of tarantulas, wolf spiders, and other (apparently) terrifying creatures for most people. Only a few spiders are deadly to humans, despite the fact that all spiders have venom to some degree.
However, the scientists speculate that this action allows spiders to better focus their forward-facing primary eyes on unidentified things. The majority of spider species have eight eyes, while others have only six. Despite all of those eyeballs, many people have poor vision.
The jumping spider is an exception, as it can perceive more colors than humans. The day-hunting jumping spider can see in the red, green, and UV spectrums thanks to filters that sit in front of cells in their eyes.
Because complex vision originated independently in vertebrates and arthropods, the ability to discriminate between living and non-living motion based on joint relative positioning most likely arose convergently in the two groups of animals.
“Jumping spiders’ secondary eyes confirm themselves to be a marvelous tool,” the researchers add.
“In this experiment, we observed how they alone can tell apart living from non-living organisms, using the semi-rigid pattern of motion that characterize the formers and without the aid of any shape cue. Finding the presence of this skill, previously known only in vertebrates, opens up new and exciting perspectives on the evolution of visual perception. My co-authors and I can’t wait to see what other visual cues can be perceived and understood by these tiny creatures.”
