Weird Nature Spiders Can Count, Just FYI  

Kate Jacobson
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Hey, how's it going? Having a good day so far? Great, great. Oh, just wanted to let you know spiders can count – specifically they can count the number of prey they've collected, and they know when they need more food. Great times.

Scientists in Wisconsin figured out spiders have a sense of numerosity, AKA they can differentiate quantities. They know how many insects have fallen into their webs and if they need to get more. If it's not a certain number, they know they need to go hunting for more. It's unclear whether all spiders have this ability, but some arachnids definitely do - including the golden orb spider. So hey, not all spiders know when to start hunting you so try to sleep easy tonight, okay?

Golden Orb Spiders Know When They Need More Food – Because They Can Count

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Photo: danorth1/flickr/CC-BY-ND 2.0

Scientists at the University of Wisconsin figured out that one particular type of spider – the golden orb spider – has a sense of numerosity. In other words, they understand quantities. Specifically, they know how many insects are trapped in their webs, and they know whether they need more. According to researchers, the spiders have a threshold of insects they want in their web at any given time. If that number reaches below said threshold, they know it's time to be on the hunt again. 

They Also Know Differences In Mass

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Photo: jeans_Photos/flickr/CC-BY 2.0

Researchers hypothesized golden orb spiders could count, but to prove this, they needed to rule out the possibility that spiders weren't just capturing food based on the weight of the web. Golden orb spiders are known as "sit and wait" predators, meaning they can have multiple insects on their web at one time. When prey is removed from the web for eating, they know they need to replenish it. But the question was: Do they just notice the web weighs less? Or, do they know how many items were removed

Scientists did a test where they removed several items during one experiment, and one big item during another. The spiders knew the difference between multiple insects versus one big one. But when they did remove a big one, they noticed it was big. They would try and replace their prey with one of similar size. Meaning they understand the differences of mass too. 

They're Not The Only Animals That Can Count

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Photo: THEfunkyman/flickr/CC-BY-NC-ND 2.0

Numerosity is obviously something we humans have, but you might be surprised at just how many animals can count too. From fish to rats, and birds and dogs, several species of animals can compare numbers in one way or the other. Some primates – including chimpanzees – have even been known to work out simple fractions and addition, based on what some experiments have shown.