Credit: deviantart.com
Spiders often occupy top-billing on the bug shit-list. They alternatively fascinate and repulse us, delight and cause despair. How beautiful! (Impossibly colorful, intricate and iridescent!) How creepy! (Do they really need eight legs and possess the ability to jump 100 times their own body length?!) How helpful! (They eat all those pesky mosquitoes!) How sinister! (They can lay their eggs inside your skin!)
And I think we can all agree that unknowingly walking into a spider's web—face-first—is just about the worst thing ever. I double-dog dare you not to freak the hell out and demand to know from the nearest passerby, "is it on me?!?!" and leap about like a frightened child.
Say what you will about their nightmare-inducing ways, but some of their behaviors are downright diverting.
The latest?
Rafael Rodríguez, associate professor of behavioral ecology at of the University of Wisconsin-Milwaukee recently published a study in Animal Cognition (which, just by the way, I want a subscription to ASAP) that proves the golden orb-web spider can count.
Truth.
Golden-orb spiders are, apparently, delightful fat-kids much like myself. Firstly, they're sit-and-wait hunters. None of this rushing about and trying to chase down their supper bullshit. Oh no. They weave a intricate web—rumored to be some of the largest and strongest on the planet, often measuring 18-feet wide and lasting as long as two years—and then just kick it.
Delectable insects like beetles and praying mantises find their way into the spiders' woeful web and become what is known as a "prey larder." Which, like any good fat-kid can understand, is basically a stash of delicious treats of all shapes and sizes just waiting for you to consume when the mood strikes.
Rodriguez already knew that when other bastard spiders pilfer the goods of another spider's larder, the spider that's been robbed will search diligently for their lost prey.
Spiders that lose larger larders (i.e., spiders that lose larders consisting of more prey items) search for longer intervals, indicating that the spiders form memories of the size of the prey larders they have accumulated, and use those memories to regulate recovery efforts when the larders are pilfered. — Rodriguez, Nephila clavipes spiders (Araneae: Nephilidae) keep track of captured prey counts: testing for a sense of numerosity in an orb-weaver
What Rodriguez set out to do was to test a two-fold hypothesis: do golden-orb spiders present prey counts (numerosity—basically, the ability to count) or a continuous integration of prey quantity (mass) in their memories. Rodriguez explains that searching for a marked difference between increase in search effort according to mass or number of prey would reveal behavioral insight into how these arachnids keep track of their nibble-bounty.
So here's what they did. Rodríguez and his comrades headed to Costa Rica and did a field study. Then they gave some golden orb-web spiders some tasty mealworm larvae . . . before snatching it away and causing the spiders to start a frantic search:
We manipulated larder sizes in treatments that varied in either prey size or prey numbers but were equivalent in total prey quantity (mass). We then removed the larders to elicit searching and used the spiders’ searching behavior as an assay of their representations in memory. Searching increased with prey quantity (larder size) and did so more steeply with higher prey counts than with single prey of larger sizes. Thus, Nephila spiders seem to track prey quantity in two ways, but to attend more to prey numerosity.
In short? These clever spiders are tracking both mass (plumpness and heft of said worms) and also the amount of worms available to gobble.
While numerosity has been observed in all kinds of vertebrates from lions and hyenas to fish, raccoons and rodents, it's a bit rarer in invertebrates, although not unheard of. Rodriguez believes his study is but one foray into a relatively untapped exploration of numerical cognition within us Earth-bound species.
"The widespread taxonomic distribution of the sense of numerosity, together with the diversity in the life history of the animals that possess it, suggests that it is an ancient trait representing a basic feature of animal brains large and small. But we have relatively little information about how the sense of numerosity varies with the ecology and life style of different species. This hampers our ability to test adaptive hypotheses about the evolution of numerosity, although it is clear that animals use it in crucial activities such as aggression, group formation and foraging."
In fact, some scientists have postured that numerosity is humans' "sixth sense," likening the brain-skill to that of an abacus, which maps numbers in space.
Now if only we could develop a seventh sense that lets us know when these devious, food-stuff-counting bastards' webs are about . . .