Have you ever come across a rolling swarm of Sawfly Caterpillars?

Imagine you're deep in the forest, and you come across this.. thing. It's a group of caterpillars, moving in a formation known as a rolling swarm.
If you're anything like me, your first reaction will be to get down to their level and study them.
What are these caterpillars are up to Why are they moving in this strange way?
The first thought is there is safety in numbers. Which one will the predator pick given that there a couple dozen of them?
So I looked further into this phenomenon and there is another reason.
There is a simple, but mind-blowing idea. Anyone who's been on one of those endless moving walkways at airports knows that if you walk on a moving belt, you'll get to the end faster.
And so these caterpillars have essentially built a caterpillar-powered conveyor belt. Unlike a typical conveyor belt, this one never runs out, because the caterpillars keep disassembling and re-assembling it.
The really surprising thing is that this entire rolling swarm of caterpillars moves faster than any single caterpillar can.
The caterpillars on the top are getting a speed boost. But the ones at the bottom are still trudging along at their regular speed. So why does the entire group get a speed boost?
Every caterpillar spends some time on each 'floor'. At the ground floor, a caterpillar moves at normal speed.
The next floor up, it's moving at 2X speed, because the floor is moving forward and so is the caterpillar.
The next layer up, it's moving at 3X speed, because the floor is moving at 2X speed, and so on.
Every single caterpillar has spent some time moving slowly in the first floor, and some time moving faster in the higher floors.
On average, its speed is somewhere in between - faster than a lone caterpillar, but slower than the caterpillars on the top.

These Caterpillars are not the grubs of a moth or a butterfly.
It is the grub stage of a Sawfly.
Sawflies are closely related to ants, wasps and bees though they do not possess a sting.