The key to this NM and LL is the placeholder. I was out in Valk for about 2 hours one day watching 3-4 people kill every fly in 2 grid squares. I got bored and logged near the palm trees in the SW corner. Logged back in about 6 hours later, WS, nothing. Ran off chasing another fly when I saw a fly in my peripheral, turned, targetted, claimed, killed and got drop.
I don't see what the fuss is about. I'm 1/1 on him as a 51THF/25RNG. He took me from 818/818 to 718/818 after using Venom and Cursed Sphere.
I did the PH trick with LL and it spawned within 5 minutes of killing it. So if you're hunting this, just kill the PH and wait for it to respawn. Stop killing every fly out there.