This is a complicated question, and I am new at this so I will totally defer to the more senior members of the forum if they have more wisdom. However, I found a website that might be helpful. It relates only to the Monarch butterflies. It gives you the peak migration in your area, if you know the latitude. The latest release date would be two weeks after that peak. So if you can figure on the longest possible interval from egg to emergence, since the weather will be cool, you should be able to figure it out. It would probably help to raise them in a warmer environment, such as indoors, especially at night.

I don't know about any of the other species, but black swallowtails can overwinter as chrysalides, so I would think they would be more flexible. HTH.
Liz

Here is a link that might be useful: Migration dates

Thanks Liz, that link is very helpful.

I have overwintered a few black swallowtails before, so I know they at least overwinter here. I wish I had written down the dates I found the eggs and when they pupated. I know I have released monarchs in late August and early September before, but again I didn't record the dates. In the past I had just kept a running tally of each species raised that year, but now I know I should probably jot down some of the dates for the earliest and latest ones at least.

My books are all very general about this considering the audience is the whole US or beyond. They will say something like flight period May-September and overwinters as a pupa. But there is no info as far as where a particular species will overwinter and survive. I'm thinking if I am at the very northernmost point on the map for a butterflies range that they will not overwinter here. Maybe they only come this far north to breed and then their offspring fly south again to overwinter?? I just thought maybe there was some resource with that info available.

I would love to see what new species I can raise since I now have some decent sized wafer ash, wild black cherry, and false nettles started. So far I have done monarchs, black swallowtails, american ladies, clouded sulphurs, and hummingbird moths. The tigers are so abundant now I'm itching to get some eggs. A giant swallowtail would be like my holy grail!

Hi molanic, I'm in Minneapolis and have released monarchs in early October the past 4 years so you still have time.

I would suggest bringing them inside during any cool spells so their metamorphic process doesn't slow down. I just got eggs today in Minneapolis and I usually get eggs until the first week of September. Hope this helps, Tony

Thanks Tony. I will have to keep checking for monarch eggs for at least another few weeks. The swamp milkweed looks pretty ratty, but the a. syriaca, a. curassavica, and a. tuberosa still look good so hopefully I will get lucky.

I have always raised them indoors anyways because I don't have a very good setup outside for it. One year I tried outside with a big pop-up enclosure and potted tropical milkweed and it didn't go well. It was too windy for it, hard to clean, and several pupated on the zipper so I couldn't get it open very easily. A few also fell while pupating due to poor location and didn't make it. So now I just do cuttings indoors which works pretty well for me.

Last year, I released 220 Monarchs. The last 2 eggs were collected in a nearby field (sunnier exposure than my yard) on September 2nd.

This year, I haven't seen a single Monarch in the area. :(

That is really sad, terrene.
Liz

It's terrible...
Two years ago I had 9 Monarchs to one Liatris. Now I have two lonely Monarchs around six plants in full bloom. Sad, and scary too.

In SC, we will definitely have BST's overwinter here. Usually the eggs are collected in late August or September. I had a few overwinter last year I (I also learned my attic is not the place for them unless you want butterflies in March!). This year, I have no clue how that will play out since our weather has been so strange and we are just now starting to see very many adults. I seven right now that are in chrysalis and five more on a plant. Most of them should start traveling today or tomorrow. Last year, I had my first monarchs ever and they were not until mid-late September. I ended up releasing them just as the monarchs were migrating through the area last fall.

We live in Richmond Virginia and I've released about 20 Monarchs so far, with 20 + more in 2 butterfly boxes and maybe 12 on the milkweed plants in the garden. It's getting late in the season and I still see Monarchs coming to presumably lay eggs. I'm thinking of cutting the milkweed back (putting the caterpillars in shelters) so they won't stop here this late. It will get colder soon. We put the boxes in the garage at night and in the sun during the day.