Donna, if the caterpillars have little black horns on both ends and yellow stripes, they are Monarch cats. If the stripes are whitish, they are likely Queens.
I don't think these are monarch's. Monarchs lay their eggs on milkweed/asclepsia family and the yellow is a stripe pattern not the little crown pattern . I think you have old world swallowtails. maybe you get to see them pupate and then you will know for sure.keep a close eye on them. They all may disappear due to the birds. I had lots of them on the fennel, but I think the birds snatched them all.
Papilio polyxenes Black Swallowtail Papilio machaon Old World Swallowtail They are very similar but the dots on the Papilio machaon appear to be much smaller and more orange than the ones in your photo. Add to the mix that caterpillars of the same species can have different colorations and you have a conundrum. Keep an eye on what shows up in the garden in a few weeks. Of course, that depends on whether or not they will be overwintering in the chrysalis in which case it could be sometime next spring before you see which one they are.
I checked out the Black Swallowtail and the Old World Swallowtail. The Black Swallowtail is the one that I've seen around here a lot. Thanks for info.
