What evolutionary conditions would force arachnids to develop human-like intelligence?

Question

I am designing a creature for a tall tale I'm composing and I have apparently hit a wall when it comes to envisioning an environment that would promote the creation of an intelligent race of arachnids. A member of said species would have an average height of two meters, possesses a brain capacity to formulate tribal societies and is able to fashion for itself bronze and iron weapons.

What kind of habitat would encourage these changes to a spider that starts out as say, a species from the portia genus?

Answer 1

You can't, assuming anything like Earthly biochemistry*. Neither the exoskeletal structure nor the breathing apparatus can be scaled up to anywhere near that size.

What you perhaps could do is have a world with arachnid-like creatures - 8 legs, multiple eyes, &c - based on a more vertebrate-like body architecture with an endoskeleton, lungs, and a circulatory system.

*Assuming they live on land. Ocean-dwellers, like some crabs, could perhaps get that big, but that would obviously preclude bronze & iron.

Answer 2

"On Earth, insects reached their biggest sizes about 300 million years ago during the late Carboniferous and early Permian periods. This was the reign of the predatory griffinflies, giant dragonfly-like insects with wingspans of up to 28 inches (70 centimeters)."

Quoted from https://news.ucsc.edu/2012/06/giant-insects.html

Scientists have recently discovered that this was a period when the Earth's oxygen levels were more than twice what they are today. Insects like all living creatures, rely on oxygen for their energy needs but they absorb their oxygen directly through pores in their epidermis called spiracles which feed through a network of trachea to deliver this oxygen to all parts of their body. Absorption of oxygen may well have been more efficient for insects of this period than they are for mammals today.

The other interesting property about oxygen is that it's atomic structure makes it one of the most electronegative elements on earth. This refers to the elements ability to tear off electrons from other atoms. This property makes oxygen in its pure mono-atomic state, highly volatile, lending itself to chemical reactions which yield huge amounts of energy!!!

This is key as it provides an environment conducive to the evolution of brain power.

Other environmental drivers will be needed. This may come from a need to hunt for and outwit their prey.

Take a look at the evolution of birds from reptiles to study how again intelligence became efficient, weight for weight of brain matter. Then draw parallels to the evolution of your arachnids.

Answer 3

You would want an environment where the spider has a longer lifespan and smaller brood size. This way the spider species survives by learning instead of mutation. Next the spiders have to have a reason to work together, possibly to hunt larger and larger prey animals.

Answer 4

You cannot have earth type insects that big, and if you did, these things would overpopulate very quickly because insects have a LOT of offspring.

So make up an animal that looks a bit like an arachnid but has a totally different gas exchange system and breeding cycle will give a you a start.

The intelligence part would be easier, there are already spiders that group-construct huge webs and cooperate to take down prey that weighs a hundred times more than an individual spider. As many as 10,000 of these may inhabit one huge web.