Lot’s of people including me couldn’t complete the quest at least how it should be completed, there are 2 solutions in my opinion, the golden ant you suppose to capture is in flooded caverns to the right from mansion, but ant is on a small wooden bridge in a cave and you can not swim while you carry anything, you can only reach that area by swimming so, first suggestion is there can be separate caves in that area and you have to swim through flooded areas to reach next one but there should be a small gap between them which you can not pass but throw something so when you reach the ant and capture it you can throw it to the cave next to it to the left through that small gap or crack then you swim to that area and do the same to the cave the the left then you capture the and leave the caverns and bring the ant to mansion, or easier option there can be another teleporter for that area and if you activated one near the mansion you can teleport there with ant and complete the quest, also for this quest and other there can be more specific info so players won’t get lost, for example you could be asked to find a rare golden and which is rumoured to be in flooded caves so you would know where to look and for people confusing different colour ants or other monsters golden ones can have a glow or sparkling around them and golden monsters could be stronger as well like needs 2 or 3 hits to destroy unless you throw them into traps or water (unless they can swim 
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Golden Ant Quest
That’s an interesting idea, spitting stuff through an opening not big enough, or otherwise not possible for you to jump through. The quest isn’t impossible though, of course. There’s a golden ant in Burn & Bubble, and in a secret area in Rock a Fort. There’s also golden ants and a teleporter in the forest later on.
I got mine from the forest - took a bit of effort, but nothing exceptionally hard. I also believe that the biologist thing could be expanded in some ways, like have more conversation or have him pay you for bringing some other critters.
“how it should be completed”? “supposed to capture?”
Why is this the golden ant you’re supposed to capture? Why not the first one in the game (in Stonepipe Meadow)? Remember, there’s also a transporter on that level. If you’re like me you first try giving an orange any thinking that they are the golden one. Or a platform one. When that fails you either keep playing and hope to figure it out, or if you’ve been paying close enough attention, you’ll realize that you just passed a golden ant a level back. So you run back through Stonepipe Bridge, and back through a bit of Stonepipe Meadow, scoop up the golden ant, run back through to Secluded Hut and give him the golden ant.
You can actually carry it through the level and to the next level Stonepipe Bridge and beat the boss and keep it on the bridge. Unfortunately, when you beat the boss you are moved to the next level automatically and leave the ant behind. But if you’re playing the game for the first time you don’t know that you need a golden ant. So you play through the levels, beat the boss, are told to get a golden ant and play back to get it. Or forwards. It doesn’t really matter I think. I’m just wondering why people think the flooded caverns one is THE one that your SUPPOSED to catch. It’s not the first in the game. It’s just the first after Secluded Hut. Isn’t that’s sorta irrelevant once you have transporters anyway? And since transporters are introduced on that level, is there any supposed to really?
I don’t think you’ve got to change anything about that quest - after a while I remembered to have seen a golden ant in Stonepipe Meadow and it’s rather easy to get.
If you can’t find a golden ant: well, that’s one heart capsule less for you. That shouldn’t keep you from finishing the game.
What could be done easily i.m.o. (without any necessity), is to make one of the next characters you encounter tell you about a golden ant in Stonepipe Meadow, if you haven’t finished the quest already (the birdy could have seen it, for example).
okhun’s idea about spitting sth. through a narrow opening sounds good, however, and could perhaps be implemented elsewhere in the game…