It depends on how you define decentralization. Ants, bees, termites operate in semi-autonomous fashion but with incredibly rigid behavioral repertoires and fixed roles, including more rigid hierarchies than anything humans have ever realistically constructed. So while the individual ant or bee is wandering around, and order is emerging from termite mounds, the larger context in which that order emerges is not like you intend, I don't think.

Out of Control covers this exact line of thought in depth. It doesn't focus on decentralization intentionally but by focusing biological systems, whose complex forms are nearly always decentralized and require coordination, it's almost entirely about decentralized systems.

This is similar to thinking about anarchy. Anarchy means no rulers. No third party above the two+ parties in an interaction. Most of our interactions have no third party yet we seem to be programmed to believe anarchy will not work. Maybe I'm missing your point but I think it would be harder to come up with a non-decentralized structure in nature. It is complete anarchy with no central authority. You might have small parts like a wolf pack or ant colony that have centralized control but really... you can make a point that the "leader" is replaceable and just filling a function until their utility is gone. The system as a whole is decentralized.

Flocks of birds.

Nature as a whole is a decentralised system that adapts and changes to the situation. There is no single creature (except man) that can or tries to assert absolute control.

Fungi/Mycelium

For some reason, the Portuguese man o' war came to mind for me. It's a dang crazy critter.

Portuguese man o' war characteristic // Analogy to bitcoin (?)

A "Pmow" floats around the ocean seemingly individually, but actually has the same DNA as all of the others "zooids" in its colony // A bitcoin node does its own thing but has the same bitcoin code; also, a bitcoiner does his or her own thing but we all are in consensus with the rules of the chain

The Pmows need each zooid to survive // Bitcoiners need miners to verify the chain and we also need users, traders, etc. and a community to keep bitcoin truly alive (miners alone MIGHT mean bitcoin is alive, but is it really? or is it just some computers running some software?)

My fave: Pmows literally sail the ocean with their "dorsal fins" or sails poking up out of the water. Somehow, they develop as either right or left "handed" sails. So, half of the group sails to the right and half sails to the left. This way, if they sail up on shore and die, it's only half of them...the other half sailed the other direction. // If bitcoin gets "shut down" in country X, country Y will continue on.

Pmows use their tentacles to zap little fish. // Bitcoiners zap zaps.

Pmows are cool. // Bitcoin is cool.

Swarming behaviour comes to mind, eg shoals of fish, flocks of starlings etc. You'll see thousands of individuals working in beautiful coordinated unison without a central controlling authority, simply because each "node" is implementing basic self-preservation rules.

fungus

Termites, similar to ants

Nothing will beat Nostr in decentralization given time

Mastodon is one

THE SOLAR SYSTEM IS A DECENTRALIZED STRUCTURE.