All Silksong flea locations for The Lost Fleas quest

Finding all five fleas for Fleamaster Mooshka in Hollow Knight: Silksong is a little similar to tracking down the caterpillar grubs in the original game. The main difference is that instead of finding hundreds of them, for now, at least, you'll only have to locate five across the lower regions of Pharloom.

You can undertake The Lost Fleas quest from Fleamaster Mooshka in The Marrow, shortly after you leave Bone Bottom. All five fleas are located in areas before Greymoor and the higher areas of Pharloom, so here I'll run through all of their locations and what you'll get once you return them safely to the flea caravan.

Flea location #1: The Marrow

The first flea is located in The Marrow shortly after you defeat the Bell Beast.

1. Head right out of the boss arena, past the bench room, and right into the big open chamber.
2. Hit the lever that opens the shortcut, but instead of going right into the Deep Docks, climb the platforms to the top of the chamber and into the room above.
3. The flea is in the upper right corner of the room—head left along the platforms and ascend up to the top, then drop down just after you fight the second big skull enemy to find the flea in some vines.

Flea location #2: Deep Docks Bellway

This one is nice and easy to find. In the Deep Docks Bellway, smash the left-hand wall (just to the left of where the Bell Beast stands—you might have to jump a bit). You'll enter a room with a lava-based platforming puzzle, but it'll lead to the flea which is directly above the entrance.

Flea location #3: Also Deep Docks

Another easy one. Right after you acquire the Swift Step ability from the shrine, use it to jump left across the platforms in that same room. Hit the lever at the far end to lower the bell and use it to jump up to the section above where the flea is trapped.

Flea location #4: Far Fields

The fourth flea is in Far Fields. To get there, you need to:

1. Head to Far Fields Bellway, (you'll need the Drifter's Cloak you get from the Seamstress to get here), then exit and jump left across the chasm and into the room on the other side.
2. Head left across the platforms and up into the next room.
3. Go to the far right side of this next room and smash a secret wall.
4. Hop up a couple of platforms to spot a passage on the right blocked by some bone containers.
5. Smash these and head inside (be warned, a red ant will catch you, so smash out of the cage), then smash the flea's cage to free it.

There is an alternate way if you don't have the Drifter's Cloak yet. While heading into Far Fields via the main path, look for two red ants on a platform above you, huddled around a lantern. From here, you can sprint and jump up the platforms to reach the top of the room instead (and then go from step 2 in the list above).

Flea location #5: Hunters March

The final flea is in the Hunter's March area. You'll have to defeat the big red ant boss guarding the passage on the far right side of The Marrow, but you can do this easily once you acquire Swift Step. This is the passage to the right above the prison with the bench where you meet Grindle, in case you're lost. After he's beaten, you simply have to use downward attacks on the red orbs to bounce yourself all the way up to the top of the next room, where you'll find the flea.

Go see Fleamaster Mooshka after you've located all five, and he'll take you to the far left side of Greymoor, which effectively skips a huge chunk of the main path. You'll also get three charges of Flea Brew if you talk to the other fleas at the caravan, which boosts movement speed and attacks temporarily.