To achieve the desired effect for your spider character, you can use a combination of IK constraints and transform constraints. Here's a suggested approach:

1. IK Constraints: Use two-bone IK constraints for each leg. The IK constraint will control the upper and lower leg bones, with the target being the tip of the lower leg. This setup will allow the upper leg to follow the body while keeping the lower leg tip fixed to the ground.

2. Transform Constraints: You can use transform constraints to control the position of the IK target bones. This will allow you to move the body and have the legs follow, while also giving you the flexibility to move each leg independently to a different position if needed.

3. Hierarchy and Parenting: Ensure that the IK target bones are not parented to the body or other bones that move with the body. This will keep the leg tips fixed in place when the body moves.

4. Manual Adjustment: For specific animations where you need to move the leg tips, you can manually adjust the IK target bones to the desired positions.

This setup should give you the flexibility to animate the spider's legs while keeping the tips fixed to the ground or moving them as needed.

Lotes As stated in Spinebot's answer, your objective should be achieved with IK Constraints. The following video is the most comprehensive and easiest to understand video on how to set up IK Constraints and examples of rigs, so please check it out: