This was really cute, I loved the caterpillar lol! The tongue attack move too, pretty funny. I think the chain burst damage was interesting, although it didn't always work out for me, one of the big boss ants kept absorbing the acid blobs before it could detonate the others.
Gravity seemed a little inconsistent at times, since sometimes I could move totally vertically but sometimes I couldn't wrap around tunnels in a way that made sense to my brain, but it didn't get in the way of anything so I'm not complaining. The lil guy also had the tendency to wig out, I think around the corner where he stops detecting slopes. It gets especially finicky to control especially at the start of the sewers. Maybe it's viable to make him always stick to walls unless you jump? I'm not sure if that would get in the way of any limitations you had designed though. Currently though you can already skip a lot of the sewer upper area by climbing up the wall.
As someone else mentioned, some speed would feel nice, although I don't think it makes sense for a caterpillar to move too fast, so maybe some kind of dash?
The music was fitting for the atmosphere I think, but I think it could have benefited from being longer and more varied since it seemed like a pretty short loop. At least in the anthill, since that has drums and isn't pure ambience it's a lot more noticeable.
The environment also was difficult to remember, since everything in the anthill area uses the same brown tileset. I don't know the best way to mitigate this, since an underground ant colony probably DOES look all the same, but maybe some objects buried in the ground or a variety in the color of the soil could make places feel a bit more memorable. It's a long way to warp to save after all. Once I very sadly lost my acid attack, I had no idea how to get back to find it again. I mean, I did eventually stumble back to it, but I had to go a while again without it.
Health seemed kinda stingy. This is purely opinion, but it's very frustrating to go long stretches and then end up all the way back at the start as constantly as is, even when I'm taking chances and fighting enemies instead of avoiding them. One suggestion would be to use a more percentage based health system rather than stock, and then counting the leaves towards that percentage. Or maybe something like X amount of leaves will heal you 1 stock of health.
OKAY now that I've found the cocoon I see what leaves are for lol. Had no idea they were the objective, not sure if obfuscating that was necessary. My first instinct was to descend straight into the anthill, so I didn't see the save apple or the cocoon until pretty late. Scraping enough up in the end game is a bit tedious though... rather than exploring for powerups I'm just killing the same enemies over and over in the hopes I'll be able to scrounge up enough to finish the game. I'm also a bit disappointed that the only other powerup I found was "powerup you already have but slightly stronger" 😞
Slugs have a bit more health than I think is necessary, they're hard to hit even with the acid and tricky to avoid when they fall from the ceiling, and when you get to the sewers you're so low on health that you're especially at risk of dying easily. They also don't reward you well, only 1 leaf as opposed to some of the ants giving you 5 and feeling much easier to beat. (I'd put a save point at the start of the sewers)
I'd also maybe have made finding that first save apple at the top mandatory, or making the starting sac a save point, cos once I made it out of the first sewer I was SWEATING for health lol.
I did beat the game though, happy metamorphosis indeed!
I know this is a lot of critiques but I did enjoy it overall!!