You must know that implementing the IK system in Maya requires a lot of operations. However, there is no ik system support in unity, which requires developers to develop ik systems themselves.
Here is a really fancy lecture about ik system. Not only on unity but based on 3D mathematics.
The IK system is actually not complicated. It only contains some relatively elementary vector operations. The main core is to interpolate the original position of the joint with the target position, and use the distance from the target as the weight.
I won’t say too much about linear algebra here. I am going to show the demo directly.
I added another control point to this ik system to affect the mid joints.
Now that the legs and body are developed, we can start assembling the big spider!