Instars

[MikeOxon]

I was recently asked the simple question "how many instars does a butterfly caterpillar pass through" and am finding it hard to get an authoritative answer!

I looked up 'Life Cycle', under 'Biology' on this site, and was met with the message 'Coming Soon' so, Pete, please include this information when you write this bit up

The first (American)site I found on Google confused me further by stating: "Caterpillars go through 5 stages of growth. Each stage is called an 'instar.' ... As a caterpillar grows, it 'molts' 5 times before it becomes a chrysalis." Well, 5 moults means six intervening stages from egg to pupa, by my reckoning. Also, it transpired that the article was specifically about the Monarch. Elsewhere, I read that the Red Admiral has four instars. I looked through my fairly extensive library: most books only cover the adult stage in any detail. Thomas & Lewington simply states 'several' stages for the caterpillar and I couldn't see anything at all on the subject in Jim Porter's 'Caterpillars'.

So please, all you experts who breed butterflies - what's the answer?

[Padfield]

The only species I've studied in depth (but only in the wild, not in a breeding cage) is the purple emperor, and that has five instars. I have detailed and illustrated them all here: http://www.guypadfield.com/irisearlystages.html.

They do, indeed, moult five times, the last moult revealing the chrysalis. To the best of my knowledge, five instars is normal for large butterflies. I don't know if smaller ones have fewer but I would be surprised if any got away with fewer than four, as a third instar larva is a tiny little creature.

Guy

[MikeOxon]

Many thanks,Guy. I couldn't believe how hard it was becoming to find an answer!

Super pics and description of the PE life cycle, too.

Mike

[Nick Broomer]

Hi Mike,

The life cycle of most butterflies have five instars as far as i know. But butterflies that are double brooded like the Clouded Yellow, [in this country] Comma and the Small White have five instars with the first brood and, i know from experience with the three mentioned butterflies, has only four instars with the later second brood.

Hope that helps.

All the best, Nick.

[MikeOxon]

Many thanks for the info, Nick.

I suddenly remembered my old 'Observer's Book of Caterpillars' (1979) by David Carter and read "The number of moults varies between different species but it is most commonly five or six". It also defines the numbering of the instars. The old ones are often the good ones!

Mike

[Paul Harfield]

Hi Mike

Sorry to butt in on your thread. I can not help with an answer to your question but I would like some clarification of terms When one refers to an 'instar' should this term only be used in reference to a larval stage or should the ovum and pupal stage also be referred to as 'instars'

[Nick Broomer]

Only the larval stages, Jack.

All the best, Nick.

[MikeOxon]

hi Jack,

according to my Observer's book: "The stages between each moult are referred to as instars, the stage emerging from the egg being the 1st instar". I believe from this that the term only applies to the larval stage.

Mike

edit: as you said, Nick

[Pete Eeles]

Looks like the questions have been answered - and observe that I need to clean up the terminology used on the species pages, where I've tended to use "moult" so as not to confuse readers, but would much prefer "instar" (and yes, I know they're not the same thing!).

One additional factoid - some species will vary the number of instars on occasion. Glanville Fritillary is known for this - take a look at this paper:

http://www.mv.helsinki.fi/home/msaastam ... 13_JAE.pdf

Cheers,

- Pete

[MikeOxon]

Thanks for the reference, Pete. It's not easy reading, partly because of the authors' use of fairly obscure technical terms (e.g. 'eclosion' = emergence from the pupal case)

I notice from the paper that there can be 7 or8 instars, in the case of the Glanville fritillary. It is interesting to read that the number can vary, apparently to compensate for a bad winter 'diapause' experience. I must try to find out about some of the 'fast' breeders, like Common Blue, with several broods per year. Perhaps they can reduce the number of instars to speed things up a bit?

Mike