actually simple , basically can use anything for the tail when they are that small & under water , the body is brown dyed hackle herl , the thorax is cream dubbing (dry fly ) the hackle is light dun or wht or light ginger , can be tied many different ways , i would make the thorax a little darker yellow if it was to immitate the invaria or rotunda , this one is for the later dorothea , smaller & lighter arround here. might be different where your at thats all