Detect when spawned mob touches the ground?

[NewbyZ]

How can I detect when a mob spawned in the air touches the ground?

Idk, this doesn't work

    spawn a spider at {_loc2}
    set {_b} to the last spawned spider
    apply resistance 10 to {_b} for 10 seconds
    push {_b} upwards at speed 3
    wait 1 tick
    push {_b} (direction from {_loc2} to {_loc}) at speed 7
    while block below {_b} is not air:
        broadcast "De puta madre"
        stop

 

[ShaneBee]

https://skunity.com/search?search=entity+is+on+ground.#

 

[ShaneBee]

But how can I make him do something just when he touches the ground?

 

[ShaneBee]

while {_b} is not on ground:
  wait 1 tick
#dostuff