How long does a moth or butterfly spend as a pupa? Last summer my son found an interesting caterpillar (unsure of species) and we put it in a ventilated jar with some soil and some fresh vegetation. It shortly afterwards started pupating and was fascinating to watch, rotating at high speed as it span threads around itself.

It may survive, it may not, but I don't know at what point we can definitively say, "Sorry, Derek didn't make it." I realise it probably varies wildly from species to species, but what sort of range are we talking about for typical pupation. Six months? Eleven months?

So I put this question to my moth expert friend, and the answer is it depends. Pupation duration does as you surmised vary wildly between species, but we are talking about weeks rather than months, with the diamondback moth having a pupation period of roughly 3 days under ideal conditions.

However changes in exposure to light and temperature will hange the duration of pupation. It is possible for a moth pupa to enter a state known as diapause http://en.wikipedia.org/wiki/Diapause with a similar outcome to hibernation, whereby the pupae undergoes a significant developmental delay in order to overwinter as a pupa and only emerging as an adult, in the spring when conditions are more favourable and the flowers it requires for nectar are blooming.

I would be inclined to say that if you have had this pupae exposed to plenty of light and warmish conditions (above 20 degrees centigrade) for more than a few weeks then in all likelihood it hasn't made it.

If the moth species is supposed to overwinter as a pupa... and has NOT been subjected to outside temperatures (ie kept inside), then the winter diapause is unlikely to be broken, and the moth will not emerge.