With their tiny, graceful eyes, tiny jumping spiders seem to be capable of distinguishing between inanimate and animate objects.
Wild jumping spiders were tested in a 2021 experiment.Menemerus semilimbatus) behaved differently when presented with simulated objects of both kinds, in ways that indicated an ability to discern between them.
This research not only suggests that this ability exists in more animals than we know, but also shows that other invertebrates could be tested in the same manner using the experimental setup.
“These results clearly show that jumping spiders are able to distinguish between biological motion cues.” In their paper from 2021, the researchers wrote.
“The presence in jumping spiders of a biological motion based detection system deepens the questions concerning the evolutionary origins for this visual processing strategy. It also opens the possibility of such mechanisms being widespread throughout the animal kingdom.”
It makes sense, if you think about it. Animals should be able distinguish between non-living and living things. It could literally be a matter of life or death – evading predators, or chasing prey.
It was not clear, however, if tiny invertebrate critters depend on the ability distinguish between motion and movement, or animate or inanimate objects.
Due to their exceptional vision, jumping spiders seem like a good candidate for testing. Although they have eight eyes like other spiders, jumping spiders also have two large, sparkling pools in limpid black at the fronts. Perhaps give them tetrachromatic vision.
A team of researchers led by biologist Massimo De Agrò, formerly of Harvard University, collected 60 specimens of M. semilimbatusThese spiders are common in the Northern Hemisphere. These spiders were then subjected a specially-designed point-light testing.
Here’s how it happened. Human test subjects were able to recognize the pattern of motion as belonging a human when they were presented with 11 moving dots that correspond to the positions of the main bones on the human body. Those 11 dots, when still, won’t convey the same meaning – they’re just 11 dots.
De Agrò and his team designed a similar point-light display based on the joints of a spider. The team also designed several other point-light display ideas, including one that used the joints of a spider.
The team used a “treadmill” to show the spider how it moves. They held the spider’s head in place and rolled it over a stream compressed air.
The spider’s attempt to walk across the treadmill was taken to be an indicator of how it responded to the animations.
The 60 spiders were then presented with the point-light displays and their reactions were recorded.
The jumping spiders looked at displays that appeared less lifelike with big eyes. The randomized point light display was the most lifelike, and it had the greatest effect.
This is because of the way that the spiders see. Although the secondary eyes to the side of the head don’t have the same visual acuity as the larger eyes, they give spiders nearly 360-degree vision.
The spider will not only recognize what it sees with its eyes, but will also prioritize strange things that are in its view.
“The secondary eyes look at the point-light demonstration of biological motion, and it understands it. But they don’t get it because it’s weird. De Agrò explained in a 2021 statement.
The team hoped their system could be applied to other invertebrates like insects and snails to find out more about this ability.
All 60 spiders were returned to the wild unharmed… although maybe a little confused.
The research was published in PLOS Biology.
A version of this article first appeared in July 2021.
