Flies wont move and die anymore

And this is my FlyPikup code:

<p>
using UnityEngine;
using System.Collections;

public class FlyPickup : MonoBehaviour {

    [SerializeField]
    private GameObject pickupPrefab;


    void OnTriggerEnter(Collider other) {
        // if collider other is tagged with player ... excecute code
        if (other.CompareTag ("Player")){

            Instantiate(pickupPrefab, transform.position, Quaternion.identity);

            FlySpawner.totalFlies--;

            ScoreCounter.score++;

            Destroy (gameObject);
        }
    }
}

</p>

Not an expert but maybe try closing the space between Destroy and (gameObject) so it is Destroy(gameObject); instead of Destroy (gameObject);

I could be wrong, but it is the only thing that I see is different then mine.

<p>
using UnityEngine;
using System.Collections;
using UnityEngine.UI;

public class ScoreCounter : MonoBehaviour
{

    public static int score;
    private Text scoreCounterText;

    // Use this for initialization
    void Start()
    {
        score = 0;
        scoreCounterText = GetComponent<Text>();
    }

    // Update is called once per frame
    void Update()
    {
        scoreCounterText.text = score + " Flies";
    }
}
<p>

I'd suggest looking at the fly script, as these shouldn't impact the fly's movement/triggers. If you're convinced they are affecting the flies, remove the script temporarily.

Check that your prefabs have the scripts attached and the Transforms are set. Sometimes a script component breaks and gets reset and you need to drag the prefabs back into the Inspector fields again.