Sporg

"Detects nearby movement and fires out explosive spores that drift towards their target. If you're skillful, you can lead their spores back to them and watch them perish in a destruction of their own making. There is a lesson in that, I think."

Sporgs are enemies in Hollow Knight. They are modified fungal growths that spit explosive spores.

Behaviour and Tactics
When in range, these mushrooms sprout from walls, ceilings, and floors and spit out clusters of explosive spores (only one cluster at a time), that slowly home in on the Knight. The spores explode on contact or after a short duration. If the Knight gets too close, Sporgs retreat into the ground/wall and become invulnerable, but when a spore is still in the air, they stay open and vulnerable to attacks.

Keep an eye out for when the spore is about to detonate, as the explosion that follows deals 2 Masks of damage in a wide area of effect.

As the Hunter's Journal entry mentions, it is possible to lure the spores back to them to kill them, but it is rather difficult to do so and attacking them with a ranged Spell or a Nail Art is much easier.

Location
They can only be found in the Fungal Wastes, most notably to the east of Queen's Station.