/**
     * If the base is hit (collided with), drop resources and change back to
     * random walk state.
     */
    void OnTriggerEnter(Collider collider)
    {
        if (collider.gameObject.tag == "AntHill")
        {
            _resourceManager.AddResources(inventory.carryCount);
            inventory.Clear();

            // Make agent rotate 180 degrees.
            if (state.IsReturningToBase())
            {
                navHelper.SetDirection(-navHelper.GetDirection());
                transform.rotation = transform.rotation * Quaternion.AngleAxis(180f, transform.up);
            }

            state.currentState = EAntStates.Idle;
        }
    }