Both the egg and a freshly hatched caterpillar are easy prey for many predators. I suggest saving the egg.

Outside enclosures should never get direct sun.

KC

Here is a link that might be useful: Raising black swallowtails

Where there is one Black Swallowtail egg, there usually are more.
The ELF usually lays around 10 or more eggs per visit and generally visits 3 days in a row.
Eggs take about 5-7 days to hatch and turn dark right before hatching. This is when fresh food should be offered.

Black Swallowtail eggs are a creamy yellow. See website below.

Here is a link that might be useful: Black Swallowtail egg color

Interesting.....thanks for the posts. It very well may not be a black swallowtail egg then. I've checked my other dill plant as well as my fennel plants and have seen no other eggs. It is still there, and I'll continue to keep an eye on it, but it definitely doesn't seem to be yellow like the one on the link.

One other question: I have fire ants in my yard and primarily in my gardens. Aside from the mess of just having to deal with them, they have never been much of an issue. So, I haven't done much with them. However, given that they are butterfly predators, what are the best ways to keep them out of my butterfly garden without laying insecticide down everywhere?

I've dealt with Fire Ants before. They are nasty.
Douse with boiling water repeatedly until you see no living ants. Repeat in a week or so if ants return.

These are black swallowtail eggs on fennel:
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I thought fire ants were more of a southern species. Good to know that hot water works to kill them.

It could be that the reason you are only seeing one egg is that the others have already been eaten. If the egg you're seeing is a perfectly round smooth sphere, I would still say it's quite possible it's a Black Swallowtail.

I think describing color is a bit subjective - I have always thought of the EBSW eggs to be a very pastel green.

I say go on ahead and pluck the stem it's on and watch. Either way, swallowtail or not, it's a learning experience!

~Laura

Maybe.........this morning, the egg looked like it had turned a creamy white color, and at least half of the egg looked black. My guess is that the caterpillar was emerging. Unfortunately, I didn't put it inside before I went to work. So, I'm hoping it will be there this afternoon when I get home. If so, I will get it and bring it inside.

John, thanks for the advice on the fire ants. I plan to pour boiling water on them this weekend.

You're welcome, Spiroan and good luck irradicating those ants and raising those cats.
Runmede, Fire ants are southern; I'm formerly from Florida.