Don't go by size because it will get bigger.

It is a black swallowtail butterfly caterpillar.

Check the thread I linked below for more info.

Here is a link that might be useful: First BST eggs! a few questions...

Here are some more BST threads. They are not hot links so you will have to copy and paste them:

http://forums.gardenweb.com/forums/load/butterfly/msg0713580431140.html

http://forums.gardenweb.com/forums/load/butterfly/msg061834505729.html

http://forums.gardenweb.com/forums/load/butterfly/msg0700574123605.html

http://forums.gardenweb.com/forums/load/butterfly/msg051526243597.html

Yes, by all means, bring the caterpillar in and grow it in a jar or some kind of container. You can use a coffee filter for a top or punch holes in the lid. Be sure and keep food present and changed out as parsley tends to dry out. Black swallowtails purge before forming a chrysalis, so if you see black fluid in the jar, don't be concerned.

It will take a couple of weeks for the butterfly to emerge once the caterpillar forms a chrysalis.

Enjoy!!

Caution: It's addicting! :-) One black swallowtail caterpillar turned into several; which turned into Monarchs; which turned into...

You get the idea! Enjoy! It *is* lots of fun!

~Laura

Hi northerner, I am raising my fist butterflies this year too and everyone has been so helpful. The dill, fennel, parsley, carrot tops or whatever you use will stay so much fresher is you can put it in water. I used both a medicine bottle with a hole poked in it and some small vases with saran over the hole and the dill poked through. At first I put the jars in a mixing bowl with a paper towel in the bottom (so I could clean it out easily) and saran over the whole bowl, but then I got a pop up hamper to keep them in.

Feel free to ask more questions, there are a lot of experts here.

Here is a link that might be useful: Raising Black Swallowtails

congrats northerner!

I am raising my first BST's too and most of them have pupated the last few days. 4 of the chrysalides are brown and only one is green so I guess I will be overwintering most of them.

Since you even have less summer left than I do, your butterfly will definitely emerge next spring unless it enjoys cold Canadian winters ;)

What a fun way to say hello to spring 2012! Good luck with your cat, Tony

Thank you for all the info. and encouragement to raise this little cat. I have been very busy lately and did not get around to getting it set up in a suitable container, but I have been looking in on it every day and shielding it from predators by placing parsley leaves over it. Yesterday morning, it was in a vertical position, not munching as usual. It had grown quite fat, so I assumed it was getting ready for the chrysallis stage. I used some dandelion leaves to cover it and off we went to the Garlic Festival. As usual, on my return, I went to check on it and discovered that it was GONE!! I searched and searched, but obviously something took it. I am so disappointed. But next year, perhaps a swallowtail will find my garden again, and I will be ready for it. My buddleia is in bloom now. Perhaps that will attract a few.