According to a study published on 15th July 2021 in the open-access journal PLOS Biology by Massimo De Agrò 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. Jumping spiders are known to exist in over 4,000 species worldwide, with around 300 species occurring in the United States and Canada, including the zebra spider, Salticus scenicus.
Any animal’s capacity to sense other living organisms in their environment is critical for locating mates, evading predators, and catching prey. Because their stiff, jointed bones and exoskeletons limit the relative placement of specific bodily components, vertebrates and invertebrates’ motions differ from inanimate things.
From relatively minimal visual information, such as a point-light display that shows dots indicating the locations of the major joints, most vertebrates can recognize this biological pattern of movement. Researchers utilized a spherical treadmill to partially confine 60 wild-caught jumping spiders (Menemerus semilimbatus) and used a computer screen to present point-light displays on each side of their peripheral vision (only visible to their lateral eyes) for the first time to examine this phenomena in invertebrates.
They discovered that spiders who moved in a more organic fashion, with the lengths between joints limited, were more inclined to want to turn and face displays that displayed random motions. The findings appear to contradict spiders’ expectations that they should concentrate their attention on things in their environment that appear to be live possible prey, partner, or predator.
Subjects were given one of three types of constant-acceleration motion cues: virtual reality optic flow, physical motion in the dark, or a mix of visual and physical movements. When subjects felt they had traveled a distance that had been previously supplied to them either visually or physically, they stated. The perceived distance of motion generated by optic flow was correct in comparison to a previously presented visual target, although it was only half the actual motion.
In the dark, the perceived distance of physical motion was accurate in comparison to previously provided the physical motion, but perceptually equal to a considerably longer visually given distance. Even when the target was shown visually, the perceived distance of self-motion when both visual and physical signals were present was more nearly perceptually similar to the physical motion experienced rather than the contemporaneous visual motion.
However, the scientists speculate that this action allows spiders to better focus their forward-facing main eyes on unidentified things. Because complex eyesight developed separately in vertebrates and arthropods, the capacity to differentiate between living and non-living motion based on joint relative placement most likely arose convergently in the two groups of animals.
Because of their tiny black bodies and short legs, jumping spiders are frequently mistaken for black widow spiders. Jumping spiders, on the other hand, can be brown, tan, or gray, with faint white, gray, yellow, red, blue, or green patterns. Adult jumping spiders are generally coated in thick hairs or scales that are brilliantly colored or iridescent and range in size from approximately 1/8-3/4” (4-18 mm). Their front legs are often bigger and longer than the rest of their body.
Jumping spiders, in general, have the greatest vision of any spider species, with the ability to notice and respond to movement up to 18″ (45 cm) away. Their night vision, on the other hand, is terrible. They have eight eyes that are arranged in three rows. The front row contains four eyes, with the middle pair being particularly big.
“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. The discovery of this hitherto unknown ability in vertebrates offers fresh and fascinating insights into 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.”