Butterflies are pure atmosphere. They don’t react to the player, they don’t do anything useful — they just drift around lush areas close to the ground and occasionally land. But a meadow with a few butterflies in it feels alive in a way an empty one doesn’t, which is the whole point.
Like the birds, they have no model. Each is a small body with two pairs of wings — fore and hind — plus a little accent spot, built from flat shapes and given a colour scheme rolled from a list of real butterfly palettes (monarch, blue morpho, cabbage white, and so on).
Fluttering, not flying
A bird moves in smooth arcs. A butterfly does the opposite — it bobs and weaves unpredictably. Getting that erratic quality is the interesting part.
The butterfly heads toward a target point, but its path there isn’t straight. On top of the forward motion, it’s pushed side to side by a weaving signal made of two sine waves at different rates added together. Two waves that don’t line up produce a wobble that never settles into an obvious rhythm, which is what makes the flight look unplanned rather than mechanical.
# side-to-side weave: two out-of-step waves, so it never repeats cleanly
var weave := sin(t * 6.0 + phase) * 0.6 + sin(t * 11.0 + phase * 1.7) * 0.3
var velocity := forward * speed + sideways * weaveIt also bobs up and down slightly and stays a short, randomised height above the ground, so the whole swarm hugs the terrain. The wings clap quickly — the same sine-wave flap as the birds, but faster and through a wider angle.
Resting
Every so often, instead of picking a new target, a butterfly lands. It drops to the ground and switches to a resting state, where it slowly opens and closes its wings — a much slower version of the flap — for a few seconds before taking off again. That pause and the slow wing-fan are a big part of what makes them read as butterflies rather than just colourful motes.
# while resting: a slow open/close instead of the fast flight clap
var angle := base + spread * (0.5 + 0.5 * sin(t * 2.5))Only where it makes sense
Butterflies are spawned in clusters, and only in the lush biomes — Meadow and Forest. You won’t find them over the desert or the sea. That restriction is just a check against the biome map from the earlier post: spawn here only if this spot is a lush biome. It keeps them where they belong and makes coming across a cloud of them feel like a feature of that place.
As with the birds, a butterfly that’s far from the player does nothing until you approach.
Next is the system I find most satisfying: fish that move as a school, using three simple rules that produce flocking.