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Black swallowtail larva. It will eat some of the dill foliage, but that is a minor tradeoff to grow a beautiful butterfly. I'd leave it, or transfer it to some carrot tops or parsley.

oh yes, leave him be! we had a few of those on our dill last year, they turn into the most beautiful butterflies!
and they didnt do any noticeable damage to the dill either

I went to Google after I posted and identified this as a Black Swallowtail. The website reported that these caterpillars are attracted to Dill. This is interesting to me because I have not grown dill before nor have I seen this caterpillar or the adult butterfly until today.

same here...first time I saw this caterpillar was the first time I planted dill.
now we plant dill primarily to attract these caterpillars but I didnt find any this year. enjoy the butterflies : )

I think my wife would like to attract these in here garden for next year. The wikipedia page (link at bottom) states:

typically feeds on plants from the carrot family, Apiaceae, including dill, fennel, Queen Anne's lace, parsley, and golden alexanders. They are also found eating rue and bishop's weed.

Can anyone tell me which of the plants mentioned above would blend in best in a flower garden, it is specifically designed for humming birds and butterflies.

Here is a link that might be useful: Wikipedia - Black Swallowtail page.

Dill has pretty blue-ish green fronds with yellow-y green heads (until they mature) so I think it would look good among flowers, keeping in mind it can be 4-5 tall and the heads are about 5-6" in diameter. Ditto for fennel esp if you get a bronze type. Rue is a nice blue-green plant but beware that some people are sensitive to it and might get skin rashes working in the garden.
I would avoid Queen Anne's lace because it sends down a large tap root and could take over. Parsley is nice but it is a biennial so the flower heads don't appear until year 2. Ok but tend to look yellowish at that stage not the nice green of year one.

Do not purposely put bishop weed (Aegopodium) in your garden unless you want a solid carpet of it mixed with everything else, taking over. Carrots make insignificant foliage that could hide well around other plants until munched, and you might get some carrots to eat. There is no reason not to grow dill next to flowers. Easy to cut off the flower "branches" before the seeds fall so you don't get a dill carpet next year. Fennel is also an attractive plant but may be a thuggish perennial in your area.

The butterflies actually like to have the host plants near the nectar plants. There is a butterfly forum if you'd like to delve further. Just remember, the more butterflies you attract, the more host plants will be "used" (eaten.) Add some Asclepias (milkweeds) if you want to attract monarchs. I don't know which kinds do well in your area but that should be abundantly available info in a search.