Rusty Tussock Caterpillar

I first spotted a vapourer moth caterpillar on blackthorn in Butterfly Alley a few days ago. I was delighted to find another with the first lovely white field rose behind it today. Another name for this moth is the rusty tussock on account of the tussocks of bristles on the backs of the caterpillars. I've tried unsuccessfully to find the derivation of vapourer.

PS I've referred to a previous blip of mine where I suggested that this is possibly known as the vapourer because of the strong pheromones that the flightless female releases to attract the high flying males. Plausible I think. :)