User blog comment:Jojo-a-gogo/Do you guys ever wonder why Hisoka wasn't in the Ant arc?/@comment-5838283-20130105195157

I believe Togashi needed a way to develop Gon and Killua`s skills, experience and relationship, so he created a stimulating environment with new faces, abilities, and dangers.

If Hisoka had been there, it would have come down to the inevitable Gon fetish and/or challenge sequence, which unfortunately we have already seen lots of in Heaven's Arena and the Hunter Exam. (Greed Island switched it up a bit with the dodge ball match, but after that, I guess there wasn't much left for Togashi to do with Hisoka and Gon and still have stimulating new material for latter.)  But I do not deny that it would have been awesome to see Hisoka vs the ants even if he didn't run into Gon&co. I would've died too. XD