How to limit the number of movie clips on stage?

I am making a game where tempEnemy in an array of enemies gets made on random. Every time the player advances a level, more insects appear. This is how I want it to be, but when the user is high on a level, too many enemies get made that are impossible for the user to kill. How can I limit the number of enemies being displayed on stage, but not hinder the randomness of the enemy production?

function makeEnemies():void
{
    var chance:Number = Math.floor(Math.random() * 150);
    if (chance <=  + level)
    {

        tempEnemy = new Enemy();
        //Math.random(); gets a random number from 0.0-1.0
        tempEnemy.x = Math.round(Math.random() * 550);
        addChild(tempEnemy);
        enemies.push(tempEnemy);

        tempEnemy.speed = enemyBaseSpeed + ((level - 1) * speedLevelInc);
         if (tempEnemy.speed > MAX_SPEED)
         {
        tempEnemy.speed = MAX_SPEED;

        }


    }

}