Growing up in Sydney I was used to seeing the odd caterpillar or two in trees. However I've never seen this behaviour until this morning (during a work fire-drill no less!) The line of caterpillars would have been about 15-20m long...
They are known as 'processionary caterpillar' or bag shelter moth. They have stinging hairs which can cause mischief if you come into contact with them.
That's pretty cool. I don't think I have seen that before but glad you got some photos to share.
I vaguely recall it's a survival mechanism so a predator most likely a bird can only swoop down on one at a time.
As to the truth of that I don't know but it sounds good at least.
We used to gently force the lead caterpillar to attach to the end of the line. They would then circle for hours. This we called fun.
