//in your Crab class:
import java.util.List;

//...

//in your eatWorm method (or however it's called);
public void eatWorm() {
    //...
    //after eating the worm;
    List<Lobster> lobsters = getWorld().getObjects(Lobster.class);
    for (Lobster lobster : lobsters) {
        lobster.incrementSpeed(1);//or a higher value than 1 if you want to make him much faster;
    }
}



//in your Lobster class;

//...
private int speed;// = the starting speed of your lobster;

public void incrementSpeed(int speed) {
    this.speed += speed;
}

}

public void move(double speed) {
    double angle = Math.toRadians( getRotation() );
    int x = (int) Math.round(getX() + Math.cos(angle) * speed);
    int y = (int) Math.round(getY() + Math.sin(angle) * speed);
    setLocation(x, y);
}

//in the act method of your lobster class (where also the move(double speed) method is in);
move(speed);

//in your Lobster class;  
  
//...  
private int speed;// = the starting speed of your lobster;  
  
public void incrementSpeed(int speed) {  
    this.speed += speed;  
}