Was it ever explained in-comic or by Hussie why can't the trolls bear children on their own, instead depending on the contract with the giant termite skull monster? Also, is that "tentabulge" stuff canon? Most of the nsfw material involving trolls has these, and I vaguely remember Kanaya or Porrim mentioning that there's no biological difference between sexes, but I think I might be a lil' bit confused here.

They can’t reproduce on their own because they’re an insect based race. And the tentabulge is only fanon.