There was a giant spider in a tree behind my house that never seemed to move. For a month I would greet him, Jeff, whenever I left or returned home. Since Jeff never seemed to move, I got to thinkin’. How do spiders work? Do they realize they are spiders and go straight to building a web to chill on, or is that only a response to hunger? After they build a web, what happens if they don’t catch anything? Do they abandon the web to find better real estate, or do they just sit there until they catch something or get caught; or starve to death?
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Not an expert by any means but I saw an r/biology post related to this so I may have some insight. Essentially what I got was spiders have brains about the size of a grain of salt, their ability to know where they are, whether it’s optimal and whether the risk/reward if their web location is worth it is far beyond the computing power of their brains. They operate mainly off of baked in biological instructions in their DNA, that basically says “find dark corner, build web, wait for food, eat”. If any one of those doesn’t go according to plan they don’t have much problem solving to avoid death. Natures solution to this was having them create 10,000 offspring so someone is a guarantee to succeed
Jeff is big and sedentary? Sounds like Jeff is a girl. Male spiders are smaller and less likely build their own webs and eventually leave them to try and find a female to mate with. A dangerous pursuit as the females often eat them afterwards or even during.
Spiders do most of their behaviour by instinct, which is a sort of genetic hard wiring of the synapses. Instead of forming and reinforcing connections between neurons by learning, experience, and a chemical reward/punishment system they are formed embryonically in a pattern stored in the DNA. This means that spiders can build species specific webs, perform species specific mating dances and know how to hunt prey or escape predators, all without learning a thing and without ever seeing another spider do it first. That’s not to say spiders can’t learn, or that they are all the same. Spiders can learn and have their own personalities. Particularly active hunters, like jumping spiders, or social spiders.
Generally speaking spiders eat webs that don’t catch flies and relocate. They will periodically eat and rebuild nets that do work as well, to keep them effective. A decent component of a spider’s diet can be the pollen and plant matter that catches in their old webs and gets eaten along with the silk. If they build a web in a good spot they will find a safe place to hide and wait there, perfectly still, until a fly gets caught or it’s time to repair a section of the web.
As someone who has been kinda raising spiders for almost a year now, I can say that they do move sometimes. They are quite peculiar creatures, their growth seem to be based entirely on how much they eat, meaning they can look like babies for a long time but they’ll grow to adult size with enough food even if they had the baby size for a lot longer than their siblings. It’s an advantage of creatures who molt, I guess (it was very surprising for me to discover that spiders molt) Now, if they eat a lot from one big prey like, once, they just stay where they are, seemingly satisfied with just existing. At least the females do, the males just move randomly to a different web, maybe looking for females. Also, if their current web suffers disturbances too often or if they’re not capturing prey for too long, they won’t hesitate to move. If you ever wondered what they’re thinking: they aren’t, they don’t understand what they are, what is going on, that they exist. They’re little more than a robot in that regard, they have a programming that they follow but they don’t even know that.
“A million-year prejudice stares back at him. The ancient cannibal spider, whose old instincts still form the shell within which their culture is nestled, recoils in horror. He sees the conflict within them: tradition against progress, the known past against the unknown future. They have come so far, as a species; they have the intellect to break from the shackles of yesterday. But it will be hard.”
― Adrian Tchaikovsky, Children of Time
Two spider facts I’ve learned in my time:
Spider limbs operate through hydraulics. They essentially shoot blood into the limb to fill it up and cause it to extend. This is why spider limbs curl up when they die, because all the blood pools in the cephalothorax and abdomen, leaving none to extend the limbs.
Rather than mounting females to mate, male spiders ejaculate onto themselves and rub that spider semen on their pedipalps (which are like weird spider face-hands. They’ve got 8 limbs, pincers, and also pedipalps, which they use to maneuver objects in front of them), and then inseminate females using those.
I don’t know if these things apply to all spiders though. I’m sure there’s plenty of variation.
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