Knicknack will search the barrel directly down from her, looking all around it. 

Perception: 19 

She will also attempt to imitate Madam Kulp's voice, trying to coax the worms out of hiding.

Performance?: 12 

Persuasion?: 10 

While imitating Kulp's aged voice, Knicknack discovers that the barrel is full of a colorful red powder.

(Just FYI: While I will sometimes allow - or even insist upon - free perception/performance/persuasion checks during "combat", for the purposes of this market game, assume that any one check of investigation/perception/persuasion/animal handling/etc. directed toward finding/wrangling caterpillars in this minigame will cost your full action. On the other hand, feel free to make extra rolls like these in case I can use them in resolving your turn!)

Rycroft and Calista are up next!

Rycroft lights his torch and sneaks toward the door, trying not to startle any caterpillars as he opens it and examines the next room. If the caterpillars are making any noise, he produces a convincing imitation.

Perception: 12 (if lighting the torch was a full action, make it the next turn.)

Rycroft lights his torch and, reaching around Tuuli, pushes open the door to the next room. From what they can see, it is filled with furniture and clutter. (Lighting the torch was the full action.) Two additional doors lead out. No caterpillars are immediately obvious.

Calista is up!

Calista lights her torch and goes through into the second room. She makes her way to the door on the right.

On her next turn, she'll go through that door and investigate the next room for caterpillars.

Investigation - 16

Calista lights her own torch (her action) and, nudging past Tuuli and Rycroft, steps into the second room. (She may investigate next turn.)

Both rooms remain quiet. There are no signs of hiders - only seekers.

Round 2! (...of ten rounds.)

Everyone may act.

Walt calls out to his friends ,”Any signs of the caterpillars?”

He’s starting to get the impression that this will be more difficult than thought!

Walt walks over to the barrel of red powder that Knicknack found looks inside trying to figure out what it is. He slowly buries his hands digging out a handful and investigates this red powder.  

investigation check: 7

or Nature check:11

Walt joins Knicknack and examines the barrel of red powder. It seems more chemical than edible – it has a bitter smell.

Calista, Tuuli, Knicknack, and Rycroft may act next (in any order.)

Calista decides to check the couch in the second room. Maybe some of the caterpillars are having a cozy rest?

Investigation - 13

Tuuli follows Calista into the second room, grateful for her torch. Careful to not interfere with Calista’s investigation, and aware of the time limit, she leaves the door open, and moves to the eastern door, opening it.

Calista carefully examines the couch in the second room, and then scans the rest of the room. Nothing but dust bunnies and a lost copper piece. She feels pretty confident that there are no caterpillars in this room, either. 

Tuuli follows. Opening the next door to the east, she dimly sees more of the same - colorful junk, furniture, and old supplies. (Tuuli may still have her action or dash. However, Investigation or Perception checks are made at disadvantage in this dim light.)

Knicknack and Rycroft may also act next (in either order.)

(Yellow glows on map indicates torch-bearers!)

Tuuli peers o to the dim light of the new room.

Perception at disadvantage: 8 

Tuuli spots something! Just barely, in the dim light, at the far side of the couch in room H3. A tut-krogh caterpillar!

Knicknack and Rycroft may act next (in either order.)

[A note on collecting caterpillars: Once you find a tut-krogh, you might convince the caterpillar to come with you by succeeding on a Animal Handling check (that's your action), or, alternatively, you might try to grab a caterpillar by succeeding on a Dexterity (Sleight of Hand) check (also an action). ...Or maybe you have other means or ideas!]

Rycroft crosses the room to the door no one has opened yet, and carefully steps in (north side of H2).

Perception: 8

Knicknack rummages in her backpack for her candle and tinderbox. She will shuffle over to the top right corner of the first room and will spend a turn lighting her candle. 

[Candle : For 1 hour, a candle sheds bright light in a 5-foot radius and dim light for an additional 5 feet.]

Rycroft opens room #4. More must, dust, crates, furniture, and junk. And after a moment he spots something else... a caterpillar!
Knicknack lights a candle, adding more light to the party.

The tut-krogh look warily at Tuuli and Rycroft but don't move or act yet.

----  Round 3/10:

Everyone may act! (In any order.)

(Again, caterpillar collectors may try convince the caterpillar to come by succeeding on an Animal Handling check (that's your action), or, alternatively, you might try to move and grab a caterpillar by succeeding on a Sleight of Hand check (also an action). ...Or maybe you have other means or ideas!  As to the DCs...you'll find out!)

Tuuli moves ahead carefully and tries to snag the caterpillar she has spotted.

Sleight of Hand: 14 

Walt will use his dash action and move 60ft to get as close to H4 as possible. 

Tuuli darts into the dark room and just manages to grab the caterpillar before it can duck under the couch. It squirms in her hand, trying to escape. (She still has 15 feet of move left, if she wants

Walt manages to dash all the way into room#4. (Does he want to end next to the caterpillar or the unopened door or elsewhere?)

Rycroft, Calista, and Knicknack may act next.

Rycroft smiles as well as his mouth allows, and darts toward the caterpillar, trying a little misdirection trick he used hunting rats in dark alleys.

Sleight of Hand: 18