Select the body bone, choose Hide selected from the Vertexes menu.

Select all of the vertices of the rightmost "arm".

Choose Generate Bones... (Cmd+G) from the Bones menu.

1. Enter 4 in the Number of bones field.
2. Leave the 3 Letter Prefix field with its default value. This is the name prefix for all of the bones which will be auto-generated.
3. Enter body in the Parent Bone field. This will attach the base of our bone string to the model at the body bone.

Click the Okay button

On the screen you will see two letters A and B. These letters signify which side of the bones structure will attach to the parent node (body in this case). Since this is an arm, you can think of this as specifying the shoulder joint of the arm. Click the A button so that the shoulder joint of the arm is the one which is connected to the spider's body.

Select all of the vertices of the next "arm". dim3 Inspire remembers the previously entered information, and also auto-increments the 3 Letter Prefix so all you need to do is click "Okay". Repeat the previous step and choose A or B, depending upon which one is the actual shoulder joint.

Continue with this procedure for the rest of the "arms".

That's it! When you have finished with the rest of the arms, your bone structure should look like this: