Why do the moths near smoky cities turn dark?

Long ago, the moths on the trees were mostly pale. Then cities filled the air with smoke — and the moths went dark. Did the smoke paint them? Or is something sneakier going on? Let's run it and see.

1Two things to know first

Hiding in plain sight — and the color you're born with

You only need two ideas. Watch each one move:

Matching = hiding

An animal that matches what it sits on is hard to spot. One that doesn't match pops right out — and a hungry bird grabs the one it can see.

You're born your color

A moth is one color its whole life — it can't repaint itself. But its babies aren't all the same: some hatch pale, some hatch dark, like brown and black puppies in one litter.

2Meet the two moths

The pale one and the dark one

Both kinds live on the same tree. On clean, pale bark, watch who blends in and who sticks out:

The pale one

Cream with speckles

On clean pale bark it almost disappears — the bird flies right past it.

The dark one

Deep charcoal

On that same pale bark it's a black dot — easy for the bird to spot and grab.

3Your turn — smoke up the tree

Drag the soot and watch who hides now

Slide the smoke up and down. The bark changes — but look closely: no moth ever changes its own color. What changes is how easy each one is to spot. Watch the "easy to spot" meters move.

Pale moth — easy to spot?
almost invisible
Dark moth — easy to spot?
sticks out a lot
Smoke in the air: clean
CLEAN BARKSOOTY BARK

4Now let it run for real

The bark is sooty now. Watch a few moth families grow up. 🐦

Here's a whole tree of moths on dark, sooty bark — half pale, half dark. A hungry bird hunts the ones it can see, then the survivors have babies. Run it round by round. But guess first.

Guess before you run it

Soot turned the bark dark. Over time the moths on the tree go dark too. How?