Biomes are 3D now: why the biome under your feet is not the one on the surface
Cave biomes generate independently of the surface, which changes mob spawns, water colour and where structures appear. What that means in practice.
Biomes used to be a flat map: one biome per column, top to bottom. They are now volumetric, and a lot of confusing behaviour falls out of that one change.
Surface and cave biomes are separate
Standing in a plains biome and digging down, you can pass through Dripstone Caves, Lush Caves or Deep Dark without the surface biome changing at all. F3 reports the biome at your position, not the column's.
Consequences:
- Mob spawns change with depth. Glow squid in Lush Caves under a desert. A Deep Dark under a taiga spawns nothing on its own — Wardens there come only from shriekers.
- Structures follow the cave biome. Ancient Cities generate in Deep Dark wherever it occurs, regardless of what is above.
/locate biomegives a Y. It returns a 3D position because a biome now has one.
What each biome actually controls
| Property | Note |
|---|---|
| Mob spawn lists | per-biome, with separate lists per category |
| Grass and foliage colour | usually computed from temperature and downfall; a few biomes store a fixed colour or a modifier |
| Water colour | stored per biome (fog colour mostly comes from the dimension) |
| Precipitation | a per-biome on/off flag; temperature then picks rain or snow |
| Structure eligibility | most structures are gated on a biome tag |
The colour one surprises people: most grass is tinted from temperature and rainfall values, which is why the transition between biomes blends rather than snapping — but a swamp is the exception, with a fixed foliage colour and a swamp grass modifier that picks between two set greens.
Temperature is by altitude too
Temperature falls as Y rises above about Y 80, and snow forms once it drops below 0.15. That is why the same mountain has grass at the base and snow at the peak inside one biome, and why placing water high up freezes when the same water at sea level does not.
Mob variants are biome-driven
Several mobs pick their look from where they spawn:
- Axolotl — five colours, blue only from breeding, never natural
- Frog — temperate, warm or cold, decided by the biome the tadpole grows up in, not where the egg was laid
- Rabbit, fox — coat by biome; cat — black in swamp huts or under a full moon (llama coats are simply random)
- Tropical fish — 3,072 combinations, one of 22 common ones 90% of the time, and not biome-dependent
Frogs are the practical one: move tadpoles to the biome you want before they mature.
Changing a biome in place
/fillbiome ~-12 ~-12 ~-12 ~12 ~12 ~12 minecraft:lush_cavesWorks on a region — within the same 32,768-block limit as /fill, so a 65-block cube is refused — and takes effect immediately, tint included, but existing blocks do not change: snow, ice and vegetation stay as they were. Useful for map-making, disorienting in survival.
Browse every biome with its spawn list and features, plus each mob's texture and behaviour variants, in the Biome & Mob Variant Browser.