Triffany will ask you to catch a Shy Weenyworm in Bugsnax, but you can’t just find them crawling around the world like other Bug Snax. Instead, this guy is hiding out in a secret cave that nobody has accessed in years, and it is up to you to find it.
To find the cave, you will need to head back to where you first arrived in the area, or you can take a shortcut from Triffany straight through the rocks across from where you are talking to here.
On the cliff wall on the left side of the area, you will see a boulder with some cracks in it sitting in the wall. It is just a little bit up from the wooden ramp. This is the entrance to the cave, but it is blocked up. To unblock it, you will need to get a Spuddy to charge at you while you are standing in front of it. If you jump out of the way at the last moment the Spuddy will smash through the wall, and you can go inside.
Inside you will find some Shy Weenyworms walking around. Scan them before catching them to mark their routes, then place your Snak Trap down on the path. Activate the Snak Trap when they are in range to get them.
Once you have them, you can return to Triffany and she will eventually agree to return to the town, even though she is still made at Wampus for unknown reasons.