Flies spawning out of control

[SerializeField]
private GameObject flyPrefab;

[SerializeField]
private int totalFlyMinimum = 12;

private float spawnArea = 25f;

// public accessor can allow other scripts/classes can change it's value
// static variable creates a reference variable that is the same across all 
// instances of the class

public static int totalFlies;

// Use this for initialization
void Start () {

    totalFlies = 0;

}

// Update is called once per frame
void Update () {
    // while the total number of flies is less than the minimum...
    while (totalFlies < totalFlyMinimum) {

        // ...then increment the total number of flies
        totalFlies++;

        // ...create a random position for a fly...
        float positionX = Random.Range(-spawnArea, spawnArea);
        float positionZ = Random.Range(-spawnArea, spawnArea);

        Vector3 flyPosition = new Vector3(positionX, 2f, positionZ);

        // ...and create a new fly.
        Instantiate(flyPrefab, flyPosition, Quaternion.identity);
    }
}