Spiders are smart; Be glad they are small

Spiders, like octopuses, have eight legs. But they also share something else — like octopuses, once we studied them, they turned out to be much smarter than expected. What makes spiders even more unusual is that they are smart with very small brains:

“There’s the general idea that spiders are probably too small, that you need some sort of critical mass of brain tissue to perform complex behaviors,” said arachnologist and evolutionary biologist Dimitar Dimitrov of the University Museum of Bergen in Norway. “But I think spiders are a case of challenging this general idea. Some little things are capable of doing very complex things.”

Behaviors that could be described as “cognitive,” as opposed to automatic responses, can be quite common in spiders, says Dimitrov, co-author of a study on spider diversity published in the 2021 Annual Review of Entomology. From orb weavers who adjust the way they build their webs based on the type of prey they catch to ghost spiders who can learn to associate a reward with the scent of vanilla, there’s more going on in spiders’ brains than they usually take credit for. to get.

Betsy Mason“Spiders are much smarter than you think” on Known magazine (October 28, 2021)

There are some other life forms where the idea that brain size is a guide to intelligence is challenged. For example, lemurs, with brains 1/200 the size of chimpanzees, can pass the same IQ test.

But, as Mason goes on to report, jumping spiders, for example, can exhibit very clever hunting behavior. A group of jumping spiders, Portia, lures female spiders of another species (Eurytattus) to their deaths by mimicking the way a courting male spider shakes her nest and then attacks. They also attack web-building spiders by mimicking the tug on the web of a captive insect, adjusting the tug to the size of the spider it intends to devour. More remarkable,

If these strategies don’t work on a particular web spider, another trick from Portia is to shake the entire web so that it moves as if a gust of wind has hit it. This acts as a smokescreen to the vibration Portia creates as it crawls into the target’s spider web. In lab experiments, Jackson found that Portia will try different picking methods, speeds and patterns until it finds just the right combination to fool each individual web spider it hunts — essentially learning on the job.

Betsy Mason“Spiders are much smarter than you think” on Known magazine (October 28, 2021)

Portia spiders have big brains – compared to other spiders – but that’s probably not the whole answer to how they develop so many clever strategies. The organization of the brain is probably also a factor.

Another recent discovery is that the bridge spider, Larinioides slopetarius, turns its web into a gigantic ear, to hear over great distances:

The bridge spider uses its web as a designed “outer ear” up to 10,000 times the size of its body, according to a preprinted study published on bioRxiv on October 18. The discovery, which has not yet been peer-reviewed, challenges many assumptions scientists have had for years about how spiders and possibly other arthropods navigate and interact with the world around them.

“Evolutionarily, spiders are just weird animals,” Jessica Petko, a biologist at Pennsylvania State University in York who didn’t participate in the new study, wrote in an email to The Scientist. “While it has long been known that spiders sense sound vibrations with sensory hairs on their legs, this paper is the first to show that orb-weaving spiders can amplify this sound by building specialized web structures.”

Dan Robitzskic“Spider uses its web like a gigantic constructed ear” on The scientist, (October 29, 2021). The paper is open access.

Some spiders also master the art of pack hunting:

Spiders that hunt in packs use web vibrations to coordinate their attacks, allowing them to kill prey hundreds of times larger than they could alone.

Of the 50,000 known spider species, only one or two hunt as a group, with thousands of individuals scattered on webs that can span several cubic meters. When prey insects land on their webs, the spiders synchronize their attack and move as one to capture animals up to 700 times heavier than an individual arachnid.

Christa Leste-Lasserre“Synchronizing Social Spiders to Catch Prey Hundreds of Times the Size” on new scientist (7 March 2022) The newspaper is open access.

When the prey lands, all the spiders remain silent, to distinguish the vibration of the prey from the movement of other spiders, then they all attack. It is not yet clear how exactly they will do it.

Here’s a spider that uses silk to hoist a shell into a tree:

Some analysts suggest that in web-spinning spiders, it’s best to see the web as part of the spider’s “mind,” complicating the intelligence picture — yet clarifying it in a way:

Spider intelligence is not about abstractions or moral choices; it’s about killing and eating other life forms. What’s uncanny is how many different strategies they’ve developed to do that.

Anyway, spiders are smarter than we used to think and we’re just beginning to discover what they use their little brains for.


You may also want to read: In what ways are spiders intelligent? The ability to perform simple cognitive functions does not seem to depend on the vertebrate brain as such. (Denyse O’Leary)

and

How do insects use their tiny brains to think clearly? How do they deal with complex behavior involving only 100,000 to a million neurons? Researchers are discovering that insects have a number of strategies for making the most of relatively few neurons to enable complex behavior. (Denyse O’Leary)

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