The reason the queen ant was rooted to the spot was because it was in the same pathway as Zirrack.
When it had passed the tribulation, the ant queen had awakened the earth element and due to the suppression that came from meeting someone higher in the pathway, it was paralyzed.
Unable to move or use its wings, the ant queen tried to spit out a highly corrosive acid from its mouth, but its body wasn't responding to its command.
To show how great the suppression was, the ant queen was completely consumed by fear, but it was unable to shiver as Zirrack kept walking towards it one step at a time.
"At this point, I don't know if the kingslayer title is still fit for me?" Zirrack said to himself as his hand lit up in darkish-purple flame and he brought it to the chest level of the ant queen.