Simple enough question to ask, but one that would take almost writing a book to fully answer. IOW the list is a very long one on what can and does effect the size of an adult lepidoptera, with factors possible from the characteristics and genetics of the parental pair up to and including the first few days after an individual larva pupates. So identifying all of them and explaining the hows and whys of each would be a large undertaking, more than I'm up to now days.

Many studies have been done and many papers written pertaining to this question, usually factor specific, if you really want to find out about all of them.

I expect you'll get some simple answers too here though that may or may not be spot on or good enough for you.

Nice crop job on the picture.

Simple answers: Butterflies will pupate early when the food supply is low. Butterflies will pupate early when stressed. Males are smaller than females. This one looks like a male (claspers).

Larry, you are a tease :)! It is hard to find information on butterflies. The books in the libraries are very basic. Very few have indepth discussions on the biology of Leps. I spend lots of time searching for abstracts on topics I am interested in. It is hard even to get a foot hold at times. It would help if you have the papers author's names or key words to search on.
Cheers,
Elisabeth

I'm sure that as Larry said there are lots of factors. Some of the factors that I can think of off the top of my head would include:

Genetic - size of parents

Nutrition - quality and availability of food

Weather conditions

I see all sizes of Variegated Fritillaries. Buckeyes range in sizes as do Red Admirals, and Am Painted Ladies. I saw a very small Comma while out in the field. This Comma was about the size of a Silvery Checkerspot.

When the food source runs out, caterpillars pupate early. When you think about all the variations in people and other animals, it makes sense that not all butterflies will be the same size. There is also variation in color and pattern which confuses us greatly!!

Larry, thanks for making the effort to respond to the posting.

Sandy

Thanks to everyone for posting. I have noticed variation in the size of other butterflies but the difference in these two was quite remarkable (at least to me!). The little guy is not a strong flyer and was hanging out around the fruit this morning while his older sibling was nowhere to be seen.

Curiously I found 2 caterpillars on my crabapple tree that I think are viceroys and yet apple is not listed as one of their hosts .... so is it possible that could be a factor? But what are the chances of multiple layings on an apple when there are plenty of willows around?

Here is one of the caterpillars .... is this a viceroy?

{{gwi:532208}}

Now I see it might be a red-spotted purple caterpillar .... but I thought they used willow too?

Wow. Amazing pictures here! There sure is a difference in the size. I do not see Viceroys here in my NW GA yard. I do notice that the Eastern Black Swallowtails and Monarchs that I raise do vary quite a bit in size too.

Viceroys do use apple as a host plant.

Elisabeth  Sandy,

I should have known IÂd have to get into this further if I responded to it in the first place. LOL

Basic field guides and Internet bug guides is what many of the folks on this forum seem to post their opinions from unfortunately (their only choice probably with little real life experience). But these references barely scratch the surface on Lepidopteran morphology, molecular biology, genetics, biochemistry, etc, including the causes of dwarfism. They might be good enough answers for the noobie or hobbyist, but they are not for a Lepidopterist.

The copies of my abstracts, papers, articles and notes on dwarfism (and all other lep studies for that matter) are all packed away in storage with the majority of my reference books, so I canÂt quote titles or even authors of them from memory Elisabeth. The best I can offer you is some possible factors with brief notes that you might research. I canÂt remember all of the possible causes just off the top of my head though. Each of these can contribute to dwarfism alone, but sometimes more than one factor is interrelated.

Characteristics of each of the parental pairs DNA, although a dwarf (aberration or gynandromorph) doesnÂt necessarily pass on its genome because in a viable population it may not be as readily accepted as a mate.

Quality and volume of amino acids and sugars available to the parental pair prior to mating can effect ovum and eupyrene/apyrene production.

Body size of the female can effect ovum size and quantity as well.

Oviposition site selection by female with regards to host plant quality and quantity.

Larval synchronization to the host plant.

Larval tolerance of host plant biochemistry.

Climatic conditions (photoperiod, temperature, humidity) if less than ideal can slow or stop larval growth.

Larval disease  not all kill the host, but instead weaken and rob essential nutrients.

Larval parasitoids  same as disease.

Temperature/humidity during first few days of pupal formation.

Pupal disease, parasitoids or injury (wound).

IÂm sure I missed some, but this ought to be enough to get anyone really interested in understanding more about lepidopteran dwarfism on the path to discovery. If you want more information on any of these, do some research. Natural history museums, college entomology departments and lepidopterist societies may have copies of the studies; and topic specific books that go well beyond field guides are another place to start.

Larry

(It's going on 4 A.M. here - time for a cup of coffee.)

Jeanne - the use of apple is interesting. I have watched a RSP flit about my apple tree and wondered if it was laying on it. Now, I will go out and look.

Larry - thanks so much! It is helpful to have some words or phrases to go on for searches. Eupryrene and apyrene are going to give me hours of fun! I already am drooling over the Encyclopedia of Entomology, edited by John Capinera. It is over $500 to purchase though :(. So, I will have to inter-library loan it. The concept of larval synchronization to host plants fascinates me. Elementary texts and guides talk about flight periods. They make it sound like a switch goes off and all the butterflies of one species are out. Then a few weeks later they are all gone. Having a good year this year, and conducting surveys weekly, I see that this is not the case. So, I am interested in how they synchronize themselves (so to speak) with the weather, shortening day light, and plant growth. Fascinating!

Get some rest!
Elisabeth

It is fascinating. Some species pupate in the spring and stay in the pupa until the next spring. How do they know to do that?

I recommend getting the CD-ROM. Easy to use.

Elizabeth, it has the information that you are looking for.

Amazon has used ones for around $32.

Where did you find it on CD-Rom?
-Elisabeth

Elisabeth,

It can also be downloaded free as a 129MB PDF file (torrent client, HTML, etc). I don't have it (don't need it), but gives you another option if you want it.

Larry